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I wrote this and posted it on another forum some years back. Thinking that it may interest some of you, I’ve reviewed/rewritten it.
Introduction
Reading a recent posting about “re-biasing” vacuum tubes made me aware (NOT for the first time) that many musicians know little about these devices. Naturally, this tends to perpetuate myth and misconception. I thought some of you might enjoy sharing some thoughts about this interesting (to me) topic.
You may have read discussions on the internet about vacuum tubes. I’ve read a few and (except for websites that end in “.edu”) frequently the material is inaccurate, exaggerated and/or misrepresented. Many self-styled experts imparting vacuum tube wisdom seem to have some (or all) of these characteristics:
1. Lack of fundamental electronic knowledge which leads to
a. The “Easter Egg Hunt” technique of problem solving
b. Unquestioning imitation of “fixes” devised by others
2. Courageous willingness to experiment on expensive equipment owned by someone else
And nowhere does one find more “Betty Crocker Engineering” than when “bias” or “re-bias” is mentioned.
Additionally, some feel that vacuum tube amps require maintenance while solid-state amplifiers do not. There is truth to this and we can discuss why.
Early History and Contributors
It is reported that vacuum tubes were produced as early as the 1850’s, when vacuum pumps capable of evacuating most of the air from a sealable vessel became available. The purpose of these early tubes was probably pure science: studying the behavior of heat flow in a near vacuum, for example. It is doubtful that any experimenters working with early tubes conceived of what the devices might eventually be capable.
We first hear of commercial applications when Edison, after many trials, introduced the first successful light bulb in 1879. (A light bulb is a vacuum tube with only one element: the filament.) In 1883, for reasons that are unclear, an engineer working for Edison, William Hammer, decided to introduce another element within the glass envelope, which he called a “plate”.
(Interestingly, Edison’s successful incandescent light bulb was preceded some twenty years earlier, by early versions of what we now call fluorescent lighting. Both French and German inventors produced primitive versions of gas-filled tubes that glowed when electricity was passed through them.)
Hammer experimented with his configuration, which we would call a “diode” today. He found that, when a high potential positive D.C. voltage was applied to the plate and the negative return voltage applied to the filament, current would flow between filament and plate.
This phenomenom was called the “Edison Effect” and was not understood at the time. Edison could see no commercial value in the diode tube but Hammer’s experimental results were recorded and, as was Edison’s practice, the device was patented in the U.S.
In 1873, Professor Frederick Guthrie, experimenting with red-hot iron balls in England had noted a similar effect but he, like Edison, saw nothing of importance in the process. A few years later, also in England, Sir John Fleming duplicated Edison’s (actually Hammer’s) experiments. (Fleming, however, DID see commercial value in the diode tube and patented it in the U.K. in 1905.
In 1901, a paper published by Owen Richardson explained the Edison Effect. This paper describes mathematically what is now known as thermionic emission and is called “Richardson’s Law”. In non-mathematical terms, plate current flow is the result of the hot filament “boiling off” electrons, which are negatively charged particles. The negatively charged electrons are attracted to the positively charged “plate” electrode and thus current flow is produced.
Lee De Forest’s Contributions - Birth of Modern Electronics
In 1906, Dr. Lee De Forest (Ph.D., physics, Yale) was working with Edison’s experiment and introduced another element to Edison’s diode tube. Perhaps realizing the implications of Richardson’s Law, De Forest placed a “wiggly” bent wire between filament and plate, calling this added element a “grid”. De Forest repeated Edison’s (Hammer’s) arrangement of applying a high, positive D.C. voltage to the plate and the negative return voltage to the filament to establish current flow.
De Forest’s modification produced a significant new property of the vacuum tube configuration that came to be called a “triode” because it had three (tri) connections (electrodes). Instead of a fixed current flowing between filament and plate, as Edison had observed, De Forest could change the amount of current flow by varying the voltage of the grid.
Modern electronics was born when De Forest noted that his triode was capable of amplification by means of a characteristic we now call “transconductance” which means that the triode’s conductance (and plate current flow) could be changed by varying the input (grid) voltage. De Forest immediately saw the commercial value of his invention and he patented it in 1907, calling the device the “Audion”.
As a consequence of De Forest’s invention, long-distance communication was born. The Audion became the heart of radio and telephone communications systems of the time and germinated what has become the huge telecommunications industries of today.
An Incremental Improvement
As the vacuum tube was refined, it became apparent that using the filament as one of the operating elements wasn’t a good idea. Filaments require LOTS of current, in order to heat them to operating temperature. The batteries of the day, completely satisfactory for the low currents required by grid and plate, weren’t all that suitable for powering filaments unless they were large (and heavy).
The solution was to heat the filaments from “line” voltage, or ordinary 60 Hz A.C. (alternating current). Since the filament was also a circuit element at this time, the use of line voltage introduced “A.C. hum”. In order to minimize the hum, the separate cathode was devised, around 1929.
The separate cathode consisted of a thin sleeve of metal slipped over, and heated by, the filament. Connecting the heated cathode to the negative D.C. return of the positive plate voltage supply re-established current flow. The annoying A.C. hum produced by the filament was greatly diminished because the new cathode had no electrical connection to the filament.
What Is Bias ?
The term “bias” is not clearly understood by many people, it’s not a very descriptive term in a technical sense. “Bias” to many of us, might infer something like “prejudice, inclination, predisposition, slanted” or something similar. Here’s how the word was introduced in the context of vacuum tubes ...
Early experimenters observed that De Forest’s Audion amplifier behaved in a linear manner only within a narrow range of operating conditions. The two extremes of operation were “cutoff” and “saturation”. Cutoff describes a point at which current stops (or nearly stops) flowing between cathode and plate and occurs when the grid voltage is most positive (with respect to the cathode). Saturation describes a point of maximum current flow between cathode and plate and occurs when the grid voltage is at or near the cathode voltage.
Engineers quickly found that the most linear operation of the vacuum tube occurred when the plate current was about midway between saturation and cutoff (maximum current flow and minimum current flow). The voltage applied to the grid, which established this linear condition, was labeled “bias”. The term suggests that this fixed grid voltage “biased” or “influenced” the vacuum tube toward more linear operation.
(Solid state semiconductors also require a “bias” for optimum operating conditions. Generally speaking, they require more complex circuits than a vacuum tube to achieve linear operation.)
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11-13-2009 07:00 PM
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Power Amplification
Early triodes had many disadvantages, especially efficiency. Although they consumed large amounts of power, these devices could not amplify signals to significantly large levels. Behavior was mostly linear until the plate current started approaching the limits of saturation and cutoff. Once these limits were reached, no more linear power could be produced.
Other difficulties in producing linear amplifiers were found to be attributable to the geometry of early vacuum tubes. There was a great deal of internal (and unintentional) capacitance, which caused the tubes to oscillate when amplifier gain was high.
And there was heat – the vacuum tube was similar to a steam engine in that the filament (furnace) had to heat the cathode (boiler) to produce electron flow (steam) and perform work. In order to obtain higher power levels, higher currents were required which implied higher filament temperatures and shorter tube life.
There were other problems too, such as transformer technology which was limited primarily because of the unavailability of appropriate core materials.
To improve performance, experimenters added several new elements within the vacuum tube, calling them screen grid and suppressor grid. The addition of these new elements introduced the first vacuum tubes capable of producing more than a watt or so of output power.
Virtually all output tubes used in audio power amplifiers are of this configuration, called “pentodes” from “penta” and “electrode” (five connections). The ubiquitous 6L6 – the most popular American output tube - is in this family.
The Peak Years
During the heyday of the vacuum tube, from the mid-1930s until the mid-1950s (peaking during WW2), the devices were well characterized and manufactured under carefully controlled conditions resulting in superior quality and performance. This equated to predictable, reproducible circuit operation. (Some of the best production vacuum tubes were made in the U.S., the U.K. and Germany.)
Because of the consistent electrical behavior of vacuum tubes produced under high quality conditions, circuit designs never included provisions to adjust the bias conditions. It was generally accepted that the inclusion of variable elements to adjust tube bias was evidence of a poor design.
The performance of the vacuum tube expanded in many directions, power levels increased as did operating frequency, and efficiency was incrementally improved. Given the fact that the vacuum tube is at best a primitive, inefficient device, the tasks that it was called to perform were accomplished quite creditably.
In the early 1950s, Bell Laboratories produced the first transistor, solid state electronics was born and the vacuum tube was destined for obsolescence.
Or was it ?
The End of an Era ?
Western countries quickly transitioned their electronics industries, embracing solid state technology for efficiency, economics and performance margins over tubes. Countries with less advanced manufacturing base, like the Cold War Soviet Bloc countries, could not easily make this transition, partly for economic reasons and partly for political ones. (Since their factories did not sell at a profit, there was little incentive to invest the huge sums necessary to produce solid state semiconductors.)
Although vacuum tube manufacturing technology was all but lost in the West, it survived in isolated enclaves, usually for the political reasons mentioned in the previous paragraph. Soviets used these “antique” devices everywhere – their most modern military aircraft and naval vessels reportedly still used vacuum tubes as recently as twenty years ago. But that is no longer true, even former Iron Curtain countries now have little use for vacuum tubes except to export them to the West for musical instrument sound reproduction.
With the rapidly diminishing need for vacuum tubes in high-performance military, telecommunications and entertainment equipment, the factories in Russia, China and (formerly) Czhekoslovakia reduced their production capability. (Some six or seven different tube types are adequate to support the manufacturers of musical instrument amplifiers.)
As the higher performance tube production lines were shut down and the manufacturing engineers who supported these lines looked elsewhere for more lucrative, rewarding employment, the quality of the products of these old factories started to decline. It was the requirements of the Soviet military, after all, that had established the higher quality standards that formerly existed.
Current State of the Art
Today’s vacuum tube is a poor substitute for the products made by RCA, Philco, Telefunken, Mullins, Sylvania, G.E. and many others in the late nineteen-forties. The eastern European and Chinese products are decidedly inferior in almost every respect when compared to American and European products. Quality control is lacking, materials are not necessarily optimal, there is little engineering support in the factories. Factories are no longer subsidized by parent countries because military supply considerations no longer exist.
The result is that performance (and reliability) suffers. Vital parameters vary, from tube to tube of the same type, to the extent that probably 50% of these tubes would have been rejected from any Western tube production line of the 1950s.
Although there is still appreciable demand for vacuum tubes among musicians, there obviously exists a price ceiling that defines the quality level of today’s vacuum tubes. In other words, if the Eastern manufacturers of modern vacuum tubes made them to the same standards that an American factory employed in the 1950s, the cost of the tubes would drive the price of new guitar amplifiers (even middle of the road products) instantly into the $1500 - $2500 range !
Are There Any Good Tubes Left ?
So how do the brand-name amplifier manufacturers meet their need for quality tubes ? Well, sometimes they DON’T – that is, they don’t use quality tubes. I’ll illustrate that point later. Many manufacturers simply select from the quality distribution curve of the tube manufacturer. As an example, a guitar amplifier manufacturer might send a team to the Tesla factory to negotiate a contract for quantities of 12AX7, 12AT7, 6BQ5, 6V6 and 6L6 tubes.
After examining test data from a statistically significant number of tubes from each of the desired types, engineers from the amplifier manufacturer would determine how many tubes of acceptable performance could be expected from each lot. For example, the measured data for 6L6 tubes might indicate that only 400 tubes out of a lot of 1000 would meet the amplifier manufacturer’s minimum requirements.
The negotiation would likely produce an agreement whereby Tesla (for example) would screen their 6L6 tubes coming off the production line and “cherry-pick” those that met the amplifier manufacturer’s standards. For which, of course, an additional cost would be added to the base price of the 6L6 tube.
An interesting question is suggested by the above example: what happens to the other 600 6L6 tubes that weren’t good enough for the guitar amplifier manufacturer ? Hint: they weren’t thrown away.
Reminiscing and Comparing
Some of us (beyond a certain age) will remember when vacuum tubes could actually be purchased in a grocery store ! That’s right. At the front of some stores was a large self-service tube tester, underneath was a cabinet full of replacement tubes.
Somebody was usually standing in front of the tester with a paper bag of television or stereo tubes to test. If the meter on the tester read “gassy”, “short” or “weak” (the tube tester meters were labeled in consumer-relative words rather than technical terms), one searched through the cabinet underneath the tester to find the right replacement tube, based on a handy cross-reference chart.
Anyone owning ANY consumer electronic equipment of that era and having to routinely replace one or more vacuum tubes would have been astonished if told that he had to “re-bias” the tube circuit from time to time and ALWAYS whenever a tube was replaced. HUH ???!!!
99.999% of the population wouldn’t know what the term “bias” meant. How could the average person be expected to do this and how many might be killed or injured by the high voltages within the chassis ? Where would one take that 125 pound television set to have the tubes “re-biased” each time one was changed ?
OK, obviously NOBODY ever did this. Properly designed equipment NEVER required changing bias conditions when tubes were changed nor was any maintenance EVER required other than replacing the tubes.
What does this tell us ? As previously mentioned, that tubes were more consistently manufactured and circuits more conservatively designed so that normal variations in tube operating parameters didn’t significantly affect operation.
So how did we get the idea that guitar amplifiers have to be re-biased when no other forms of vacuum tube electronic equipment require this ? Bear with me ...
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The Psychedelic Sixties
Popular music, beginning in the sixties, began to showcase the electric guitar as never before. The reasons are apparent but the evolution of (especially) rock music revealed deficiencies in amplifiers of the day. The state of the art of audio vacuum tubes and audio transformers (and pricing strategies) precluded manufacturers from making a really good, linear, high-power tube amplifier. Some tried to replicate high-power amplifiers as used in audiophile-quality equipment (Sunn). But for the most part the need for improving the design of the amplifiers was eliminated by a simple expediency:
Musicians, lacking an amplifier with sufficient distortion-free power, first accepted then EMBRACED the distortion products of the over-driven tube amplifiers.
A technically-oriented band from San Francisco started questioning why equipment couldn’t be made better and proved that it could .... if one threw enough money at the problems. Several companies (I believe that Alembic was one) were spun off as a result of continual experimentation with amplifiers, sound reproduction, feedback suppression and personal instrument improvements.
That concept caught on with a vengeance and soon “hot rod” amps began to appear. Now the vacuum tube amplifier is the simplest design that one could devise for it’s purpose, there are far fewer parts than a solid state amplifier of comparable performance. So, fewer parts and a simpler circuit limits the amount of “improvement” one can make to a standard amplifier.
The limits of the tubes themselves had long ago been reached. The tube designs had already been pushed as far as possible by the most aggressive of all tube customers, the military ! (Interestingly, some modern tube manufacturers’ literature suggests that their tubes are more “powerful” than the old standards. Don’t buy it – if they are slightly louder than the old RCA, better believe they won’t last long !)
So there were only a couple of things for the music store “technician” to tinker with when Ralph Rocquenroll brought in his Fender Deluxe and wanted it to sound like a Showman.
Amplifier Modifications
One of the modifications frequently made was to eliminate (or reduce the effect of) any feedback circuits in the amplifier. The most common is a resistor-capacitor combination connected between the speaker output and the cathode of the second or third pre-amp stage.
Although no actual power increase was possible from this change, the amplifier was less linear, had more gain (but NOT more power) and a different frequency response. As some have previously stated, a tube amplifier in light distortion, sounds “louder”. Lots of people paid lots of $$$ for this “improvement”.
Another similar modification was to eliminate (or reduce the value of) the cathode bias resistors sometimes found in output stages. A poor choice from a reliability standpoint, the lifetime of the tubes (and maybe the power supply and output transformers) suffered. If the modification was made to a pair of push-pull tubes (almost all output stages) then it was virtually certain that the two tubes were no longer biased the same. This unbalance would result in distortion and frequently would produce LESS output power as a result of the imbalance in the circuit. (Perhaps the enhanced distortion made people think that their amplifier was “hotter”.)
In an effort to preserve the (very tiny) increase in output power by eliminating the cathode resistors in the output stage and restore balance, a common practice became the inclusion of a potentiometer (or variable resistor) to vary a negative D.C. voltage on the grids of the output tubes. This made it possible to balance the bias of the push-pull tubes and still eliminate the cathode resistors. But the technique is not a very good one, especially for bias stability ... the two tubes can become unbalanced again over time and temperature The cathode resistor configuration of bias is always the preferred one.
At any rate, just about all of the modifications that people tried on their tube amplifiers did result in one significant change: more distortion. And given the increasing usage of outboard distortion products (remember the Big Muff Pi ?), more distortion seemed to be universally perceived as a good thing.
Manufacturer Responses
To be fair, amplifier manufacturers responded to some of the market pressure and actually did increase the power levels of some products. For the most part the increase in power, however good it looked on a sales brochure, was not significant.
As an example, the iconic Fender Twin in one reincarnation was increased from about 85 watts to around 100 watts, as I recall. That would seem to be a pretty substantial increase, right ? Well, actually, no.
Most authorities of the human ear agree that the minimum difference in music power level that the ear can detect is about 1 decibel. The increase in power from 85 watts to 100 watts is 0.71 decibels, so the average listening human ear could not discern whether it was being tormented by an OLD Twin, with all the controls set to “10”, or a NEW Twin, similarly adjusted.
Manufacturers also increased the gain of the preamplifier stages far beyond what was required and introduced the “master” volume control so that distortion could be selectively controlled. Unsaid, however, was that increasing the preamplifier gain also introduced more noise. The Fenders of the 1970s, for example, produce more “hiss” than their predecessors, all things being equal ...
As guitar and amplifier demand and sales increased, amplifier manufacturers were caught up in escalating power level competition. It was demonstrable that, all other things being equal, a purchaser would always pick the amplifier with slightly higher power (even if design compromises had been made to achieve the higher power and even if the power increase was completely insignificant).
Some of the more conservative design practices of the past disappeared, feedback and bias networks were altered or eliminated, power supplies were more highly stressed and so were the output tubes, all in an effort to squeeze a couple more watts out of old, reliable designs. Bias adjustments started to appear in circuits that employed grounded cathodes, instead of the safe, reliable cathode resistor circuits of the past. The factories started imitating the tinkerers in music stores, sometimes to their great regret.
The profit motive naturally produced some cutting of corners (recall the CBS fiasco at Fender). All of this, added to diminishing standards of vacuum tube performance, eroded what had formerly been idiot-proof designs typified by amplifiers requiring no expertise to maintain other than the physical coordination required to remove an old tube and replace it with a new one.
Case Study: New Amplifier Using Modern Vacuum Tubes
I was given a new Epiphone Galaxie 25 a couple of years ago by my Uncle, who enjoyed his Galaxie so much that he bought me one. Mine didn’t bring me much initial happiness - it had a problem that I’d already read about.
Music store “technicians”, as well as buyers of these amps, had written reams about the “fixes” that they employed to eliminate the awful 60 Hz hum that characterized many of these Korean Epiphone Galaxies. I read the “solutions” that were posted on the internet and was astonished and horrified to find that people paid hundreds of dollars to “fix” a $250 amplifier !!!
Since my Uncle loved his Galaxie, I knew that there was potential in the little amplifier. I heaved mine up on my lab bench and within five minutes had a quiet, sweet-sounding 22 watt (NOT 25 watt) amplifier which I now use often. It’s time consuming to describe what I did to the amplifier in those five minutes but it did NOT include re-biasing. (However, if you have one of these, have some aptitude and want to suppress the annoying hum, write me and I’ll post my fix.)
Several things became apparent from the previous exercise, gain was inconsistent and so was the shielding around the filaments, from tube to tube. Mechanical construction was not that good and, in vacuum tube manufacturing, the precision and quality of the mechanical construction is incredibly important, ranking right up there with the selection of filament/cathode coating materials (and the vacuum seal).
(I should mention that the manufacturer of the Epiphone Galaxie 25 did not produce the vacuum tubes in his product, no doubt they originated in Korea’s large neighbor to the northwest.)
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Performance versus Marketing
The Korean manufacturer of the Epiphone Galaxie 25 could easily have provided a quiet, sweet-sounding amp from the git-go if he chose. He could have imposed strict quality control on the vacuum tube manufacturer rather than buying the cheapest tubes available. He could also have selected slightly higher levels of tube quality, paying accordingly, placing the better tubes in the most sensitive circuit locations. BUT both of these options would have driven the price significantly beyond the initial target (I think that these Galaxies initially sold for around $200) so the marketing strategy seemed to be as follows:
Price the amplifier low and if the amplifier happened to be assembled with “bad” tubes, address buyer concerns by recommending that they take the amplifier to a Gibson-authorized dealer for correction. And that’s NOT a bad strategy except that the marketing staff at Gibson/Epiphone might have made an assumption that caused the eventual withdrawal of the Galaxie from the market after only a few years of production.
Perhaps they assumed a level of competence in their dealer repair organization that just wasn’t there. In my opinion, the problems experienced by most buyers could have been corrected in less than fifteen minutes at minimal cost and generated significant brand loyalty. (This little amplifier is just sweet when the buzz is eliminated !)
On the Gibson-sponsored website, the description of modifications performed by “technicians” to obtain quiet operation is horrifying. One can feel twenty-dollar bills quietly slithering out of one’s pocket as these “experts” post evidence of their ineptitude (and seemingly with pride) !
I hasten to add that these are not Gibson technicians, just people writing in to the Gibson bulletin board. While I have doubts about dealer (music store) technicians, I don’t have any reason to suspect that the level of competence at the Gibson factories is not high.
Here Comes That Bias Stuff Again
I found that the factory design of the Galaxie 25 included bias adjustments for the two output tubes. I didn’t care for the way the adjustment was implemented so I wrote to Gibson and complained. I received a prompt response from their “help” staff, including an operator’s manual and some schematics.
The operator’s manual even included a few paragraphs about ..... you guessed it, BIAS ADJUSTMENT. Unhappily the instructions were not helpful, so I developed a different technique.
Back to Generalities
Given that today’s vacuum tubes will probably NEVER be as consistent as those of the past, is it still possible to produce amplifiers that sound as good as the old ones and do not require adjustments ?
Oh yes, most certainly, but there are compromises, cost being the most immediately apparent. The designs could certainly be made more conservative – sacrificing a little power would make the circuits better behaved, more reliable, tube performance would be less critical and the tubes would last a LOT longer.
Some manufacturers (Fender comes to mind) seem to be doing this, their best selling tube amplifiers are not high-powered, heavy models but more modestly powered Princeton and Deluxe types, it seems.
If You Buy (or own) A Tube Amplifier, Will You Have To Adjust The Bias ?
The answer is maybe. But probably not, if you follow a few guidelines.
Preamplifier tubes NEVER, ever require bias adjustment. There’s no provision in any circuit to make this adjustment and there is no necessity to do so. Ditto for tubes in the reverb circuit, the same for those in the tremolo circuit, likewise the phase-shift tube. So what’s left ? Only the output power stage(s).
Whether you will have to adjust the bias of the output tubes after changing them depends on your amplifier design and the tubes that you want to install. (Recommendations for features that typify a low maintenance amplifier will follow shortly.)
Tube Power Amplifiers Never Change
Since the 1930s, any vacuum tube amplifier producing more than a few watts uses an output circuit that we refer to as push-pull, class AB. These circuits commonly use two tubes (or two sets of two tubes in parallel, for the case of amplifiers producing over fifty watts).
This configuration is universal, it’s a typical engineering compromise and therefore has advantages/disadvantages. Advantages are higher efficiency and less stress on the amplifier power supply (compared to single-ended Class A configurations), disadvantages are that the tubes need to be “balanced”. Balance means that the change in current of each tube in the output stage should be equal under drive conditions.
If the output tubes are not balanced, distortion and a reduction in power is the result. Adjusting the bias of the individual tubes – in the manner most often described – usually won’t balance the output stage except under quiescent conditions. Quiescent means no input drive ... for demanding applications, it’s most important for the output tubes to be balanced when they are driven at normal volume levels.
So maybe we should re-bias the output tubes when they are being driven AND in the actual amplifier ... that’s a better solution than the usual one. Be aware, however, that there are several tube parameters that affect balance. If the transconductance or the internal capacitances of the output tubes differ, balance can never be achieved, no matter how much the bias of each stage is adjusted, except over a narrow range of drive level and frequency range.
Further, balancing the output stages dynamically (i.e. under normal drive conditions) requires special test equipment, training and knowledge – these might not be available at the corner music store.
Against the reasons for dynamic balancing, we can pose this important question: is it worth it OR will I hear the difference ? Probably not.
Matched Sets of Tubes
Those who have no means of characterizing vacuum tubes usually choose to purchase a “matched pair” or “matched quad” and that is a good idea. Tubes that have been “matched” usually will draw about the same amount of plate current at identical bias conditions.
As stated previously, this isn’t necessarily the best condition for linearity BUT, as most of us cannot match tubes dynamically, it’s about the best we can do. Naturally, we are at the mercy of the person who is doing the “matching” (many matched sets seem to originate in bedroom or garage operations, where the only test equipment available is an old tube tester – a device of limited capability).
If the person who is performing the matching is technically adept, knowsy which model amplifier he is providing tubes for, and has the appropriate test equipment, it is possible to obtain a darned good set of replacement tubes. (The tubes should be tested under the same bias conditions as the actual amplifier and selected for identical plate currents.)
Unhappily, that may not be possible -–some tube testers (especially smaller consumer models) do not have the capability of variable plate voltage and variable grid bias voltage, so it’s difficult to replicate the actual amplifier operating conditions. And of course an assumption is that the tube matching service has exact information on your amplifier’s grid bias and plate voltages and currents – that may not be true.
Despite the limitations of the tube matching process, matched sets are still a better choice than installing unmatched tubes, about which one knows little or nothing. One may get lucky and install a couple of unmatched tubes that sound great, especially if the amplifier is an older one that produces less than 30 watts.
Amplifiers producing 50 watts and more tend to be a bit more finicky about tube matching and balance. This is because there is usually little or no cathode feedback resistance in higher power amplifiers. (Cathode feedback tends to minimize differences in tube parameters, making tube replacement a lot more forgiving.)
Tube Life
The lifetime of a vacuum tube is dependant on plate current (determined by grid bias). So is the health and wellbeing of the (VERY expensive) power and output transformers, since they must carry the plate current of the output tubes. The circuit components, especially the transformers, are costly and usually selected for a specified current or power rating. Indiscriminately adjusting bias voltages can lead to failure of tubes AND transformers. Allowing unqualified personnel to make “improvements” and “adjustments” to your tube amplifier can cause a lot of pain ... hundreds of dollars worth !
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Some Characteristics of a Maintenance-Free Amplifier
For a jazz guitarist, desiring the sound of vacuum tubes and something approaching solid-state reliability, these engineering features in a tube amplifier will help assure maintenance-free operation (no bias adjustments):
Power level of 50 watts or less (if the fifty watt level is exceeded, most amplifiers require FOUR output tubes, instead of two. The circuitry and balance requirements are more complex and matched replacement tubes are WAY more expensive).
6L6 output tubes are always desirable (since all tube manufacturers make them, there is opportunity for price/performance competition).
Output tubes with cathode resistor bias, not grid bias through an adjustment (Cathode bias will accommodate more variation in tube parameters without adjustment). Cathode resistor bias configurations are usually found in amplifiers of 30 watts or less.
Some negative feedback from the speaker output to the preamp (enhances linearity and flat frequency response, improves distortion caused by tube imbalance).
No master volume control (master volume control implies excess gain in the preamp stages which can cause excess noise and hum).
When replacing output tubes, use matched sets. (If possible give details of your amplifier to the person who is performing the match, he may be able to match them at conditions close to those of your amplifier.)
Further Thoughts
It’s best to avoid any modification or adjustment to a vacuum tube amplifier. The voltages present are LETHAL and there should be no need for the user to access areas of the circuit where these voltages are present.
If you own a vacuum tube amplifier that has been modified, consider having it restored to original configuration. You may be pleasantly surprised at the quality of the sound.
Amplifiers of around 30 watts (or slightly less) generally provide the best package of performance, portability, cost and reliability. Sound reinforcement can be used if the venue requires more volume. Amplifiers in this class will usually accept replacement tubes without any change in performance or circuit adjustment, although matched sets are recommended.
Avoid “Easter Egg Hunt” recommendations from music store technicians. A typical one is the suggestion that your amplifier should be “re-capped”. It is pointless to fix something that is not broken. (Claims for the benefits of replacing all of the capacitors are wildly inaccurate - remember that if it sounds too good to be true, it probably is NOT true.)
If you think that your output tubes need replacing, consider having this done locally, rather than ordering tubes and changing them yourself. This is NOT to say that you should give the music store technician carte blanche to crack open the cabinet !
The argument for having the tubes replaced in the store is that you play through the amplifier before and after replacement and see if there is an actual difference in performance. Make it a condition of tube sale that an improvement – as determined by YOU – has to result after tubes have been changed.
Another reason for buying/installing tubes locally is that mail order and internet distributors normally have a no-return-no-refund policy. They need to make this stipulation because of the possibility of fraudulent returns. A dishonest buyer could install the new tube then ship the old tube back in the original container, claiming that it was defective, asking for a refund or replacement.
Good vacuum tubes aren’t necessarily pricey – nor are pricey vacuum tubes necessarily good ones !
I don’t know of a source for tubes that is of significantly higher quality or provides better service than other sources. (Remember that all new tubes come from the same tired old factories in the East.) I tend to buy – where possible – from larger companies with real stores and real people to talk with on the telephone. My assumption is that there will be some accountability if I’m unhappy with the product ... of course, that’s not necessarily true and your mileage may vary.
You pay your money and you take your chance. Unless you have access to decent test equipment (and have the capability to make good measurements, especially for dynamic balance), you’re at the mercy of the distributors, so try to find a reputable one and stick with him.
Remember, when buying vacuum tubes, that you are purchasing a product that is inferior in every way to what was installed in new vacuum tube amplifiers of the nineteen-fifties and sixties. You will have to pay a premium charge to obtain well-matched sets of tubes that function reasonably well in your amplifier but you shouldn’t have to make any internal adjustments, at least that’s my opinion.
I hope some of this proves to be interesting to others, I had fun writing it !
Cheers,
Randy C.
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"Ralph Rocquenrol?" "Knowsy?" Good stuff, Mr R.
I'm sure you've seen this, but in case you haven't, here's a link to a video of the Mullard factory (UK) in the fifties.
Film Reels
Thanks.
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I cant find it now.. but I will post it later. A french video of a guy on youtube. He rolls his own tubes.
The mullard vid hit the tele forums a couple of years ago. Still a great watch. I picked up a Traynor Studiomate a few weeks ago. Original mullard tubes from their plant in Blackburn. Tubes from 1972-73 but beancounters and SS hadnt had much of an impact at that point.
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John: Thanks, my writing is most practised only when applied to technical subjects. Yes, I'd seen the Mullard film before but it's always worth a second look. (Particularly for those few of us who were born before the term "transistor" was conceived. We have a perspective - or nostalgia - that makes the film more appreciable.)
dh: I have in mind a long post regarding the design of vacuum tube amplifiers .. you have constructive thoughts about modifications to older amplifiers and I have some regarding the design of new amplifiers. Maybe we could collaborate ... enhancing understanding, reducing misunderstanding, and so forth. Interested ? For WAY too long, these amplifiers have been "copied" rather than "designed". I think that it would be nice to back up a bit and explore the process (rather a simple one) of going from paper to working amplifier ...
There are many other members that have good ideas and good understanding of the subject, from a technical aspect (Derek, are you around ?). Forum members from other countries, who don't often post, presumably because of language difficulty may want to contribute to the subject, too. I know that there are good technical minds on this forum !
Lots of people don't project their knowledge here, despite the WEALTH of it that they possess. Anyone interested in working on this - let me know, OK ? (PM) This could be fun (except for the ONE person that needs to collate/organise/summarize ... and so forth ... and be assured that "I" will try to duck that set of responsibilities this time.
cheers, guys !
Randy
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A couple of the volunteers I work with at the food pantry are electrical engineers. One spent his career working around the world on radio transmitters, and the other specialized in electronic switching in Saudi oil fields. We were talking the other day, and the oil guy said his first semester of college (late fifties) was all about vacuum tubes. He expressed some disbelief that such archaic information had any relevance in our modern world. Check out guitar amps, I told him.
The radio guy needed no such hints: he owns a Fender Jaguar (dates him right therem doesn't it) and an old Champ tube amplifier.
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Randy,
Thanks a lot for your great contribution! As a guitar player with some basic -but very limited- knowledge about the tube amps I use, this realy was eye-opening! Luckily I did already use matched output tubes, but I feel confident that with your information I will be able to get the best out of my amps (a Fender Blues Deluxe and a Guyatone Twin Reverb copy) and perhaps more importent: be able to ward off so called experts trying to sell me stuff or 'fixes' that I don't need!
And besides that: very interesting to read about the history of the tube (which proves once more that to understand the present, you need to know the history). And all that presented here in an easy-to-read package!
We are so lucky to have your here on the forum!
greetz,
Jasper
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11-14-2009, 12:56 PM #11Archie Guest
Thanks Randy! That there is a whole lot of interesting stuff I didn't know.
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Many thanks, all of you, very kind words -
RandyC
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Hi Randyc, Your vacuum tube post brings back a lot of memories for me. I am a retired EE with about 50 years of experience. Needless to say, I was in the industry doing circuit design before transistors came in. Most of my efforts were in communications design dealing with RF, Microwave & Millimeter wave circuits. However, about 5-6 years after transistors came into play, I designed and built a 100 watt guitar amplifier (home-made 12" spearker cabinet) to replace my (broken) Fender Bandmaster. It was great fun and a real eye opener for me. I used that amp at home for a few years until I bought a Benson amp to use on gigs.
When I was in college, I was working part-time as a TV/Radio repairman and very often would be one of the guys using the tube tester in the nearest Safeway. Thanks for the great post Randy!
wiz
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Thanks for your articles, Randy. You really ought to gather all this into a web site for safe keeping. (I hate to say it, but message boards do "evaporate" from time to time due to negligence on the part of the hosting provider. Not that this board is at risk, but stuff does happen.) You may want to look at Google Sites if you don't want to pay for a provider.
http://sites.google.com/?hl=en&tab=w3&pli=1
You wrote: "Properly designed equipment NEVER required changing bias conditions when tubes were changed nor was any maintenance EVER required other than replacing the tubes." I agree with the first part of this statement. The "no maintenance" part is a stretch, though.
When I was in hight school I spent my summers working as a technician in a "TV Repair" shop, back in the late 1960s. The bulk of my time was *not* spent changing tubes. Most owners of tube-based consumer electronics were quite familiar with the trip to the corner store carrying a bag full of tubes to test. By the time they called the repair shop, bad tubes had usually been ruled out.
One thing that the electronics of the day had in common was that it ran hot. Tubes throw off heat, the circuitry is in enclosed spaces with poor ventilation, ... heat builds up. The heat buildup affects some components and causes failures.
You could argue that these units exhibited poor design because they didn't effectively dissipate excess heat, and I might agree. But the reality is that components other than tubes did fail fairly often.
The three most-often touted benefits of solid state electronics were (in no particular order):
1. Reduced size and weight
2. Instant-on operation
3. Greater reliability
Point 1 is a given. Even though vacuum-tube designers were coming up with transistor-sized tubes for high-frequency applications, you still needed big bottles and lots of iron for power stages.
Point 2 was quickly and cleverly subsumed by a number of tinkerers and manufacturers of inexpensive "AC/DC" tube equipment (no power transformer) by adding a diode across the power switch. With the switch open, the diode passed current to keep the tube filaments warm but blocked the path to the B+ rectifier.
Point 3 was based upon reduced heat and elimination of tube filaments which could burn out. It took a while for some solid-state equipment to live up to the reliability claims (the earliest Fender SS amps were legendary for output-transistor failures). Manufacturers quickly got past the learning curve of discovering that transistors are delicate in a different way than tubes and needed protection circuitry as part of the power stages.
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TDD, all quite accurate.
But those points didn't fit neatly into my original intent which was to outline a brief history of vacuum tubes for those who are not knowledgeable about the topic, to dispell some of the persistent myths that musicians seem to support and to note that the industry has supported some very poor business and design practises in the past.
Some of those include:
Every time a tube is changed, an "adjustment" must be made.
"Re-capping" and like procedures to "improve performance" - darned close to superstitious or religious beliefs, encouraged by people who should know better but who financially benefit from these misconceptions.
Disconnecting circuits within an amplifier that were placed there for good reason by engineers who knew what they were doing is a BAD idea, especially when done by someone who doesn't have a clear understanding of the circuit and the results.
Mindless substitution of various parts within the circuit that were carefully selected by a knowledgeable person is a BAD idea. (Modification for the sake of modification and possibly to fill someone's rice bowl.)
Mindless copying of the same tired old circuits encourages ALL of the above - gradually all design knowledge is lost because "new" designs are actually 50 year old copies of 80 year old circuits.
Yeah, I did the TV repair thing too, when I was in high school (in college, I was a part-time machinist - better pay). I still found a few bad tubes and LOTS of tubes that had been replaced needlessly. The "consumer" grade tube testers of the time were primitive, limited and ALWAYS "erred" on the side of replacing the tube (although the tube would probably have functioned properly for another five years).
That's part and parcel of good, conservative design practise: that the engineer has considered carefully the mechanisms within the tube that contribute to performance degradation and has crafted his circuit to accomodate gradual degradation. It doesn't happen in vacuum tube circuits today - people really don't understand how they work and just keep on copying ! The only real experts are the aging engineers of the former Soviet Union. Give THOSE guys a pat on the back for designing functional equipment despite the HUGE performance deficiencies of the parts with which they worked !
Regarding transistor circuits, well that's been my career: solid-state circuit design gradually evolving to entire systems design. But transistor circuits were intentionally omitted from the discussion. Perhaps I'll get around to transistor amplifier design too. Right now, I'd like to get more people involved in vacuum tube amplifier design before we FORGET how to do it.
I love steam locomotives and, some years back, at the Railroad Museum in Sacramento, one of the docents made a comment that caught my attention. He said "The technology and knowledge no longer exists to design and build one of these engines". I fear that the same thing is starting to occur with these old tube circuits ...
But anyway, thanks for your note --- valid points. And please come back more often. (From reading back through all of the old posts, you used to frequent this forum regularly, not so much now
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Cheers,
RandyC
PS: "maintenance" differs from "repair", right ? I think your disagreement might be semantically derived ?
Also, the designers of the day understood thermal problems, in my opinion, BETTER than guys like me whose background is solid state design, they dealt with temperatures that far exceed anything normally experienced today.
If they would have had the same FEA tools that are available to me, who knows what they would have accomplished ? I had the privilege of being mentored by an old-timer early in my career. That guy could teach more in 30 minutes of observing him than two weeks of instruction/lab work. Most of us aren't in the same league as the good ones from the forties and fifties, IMO.Last edited by randyc; 11-14-2009 at 04:08 PM. Reason: PS added
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Originally Posted by randyc
I love your notion of "Betty Crocker Engineering". That's hilarious.Mindless copying of the same tired old circuits encourages ALL of the above - gradually all design knowledge is lost because "new" designs are actually 50 year old copies of 80 year old circuits.
I tend to steer clear of self-proclaimed "experts" in "toob amp design". The truth of the matter is: it's exceedingly easy to construct a tube amp that works, and not that much more difficult to design an amp that meets certain broad behavioral goals given a knowledge of a few very simple design principles.That's part and parcel of good, conservative design practise: that the engineer has considered carefully the mechanisms within the tube that contribute to performance degradation and has crafted his circuit to accomodate gradual degradation. It doesn't happen in vacuum tube circuits today - people really don't understand how they work and just keep on copying !
But most amp designers, including those who make the expensive boutique amps, seem to be doing "Betty Crocker Engineering" or "painting by numbers". Granted, their workmanship may be exemplary, but most (not all) of them are rehashing old designs with minor tweaks.
You've also alluded to the variability of tube circuitry, made even more problematic by the poor production standards of modern tubes. A lot of effort goes into tweaking one particular amp then applying those results to the broader population, with predictably unpredictable results.
I'm far more pessimistic than you. The folks who had a proper understanding of tube manufacture are already in the ground. The few who still care to manufacture tubes are simply trying to keep the old machinery and processes going as best they can. My impression, though, is that they don't have the wherewithal to proactively improve the manufacturing process, so they rely on statistical methods to try to get a more consistent yield.Regarding transistor circuits, well that's been my career: solid-state circuit design gradually evolving to entire systems design. But transistor circuits were intentionally omitted from the discussion. Perhaps I'll get around to transistor amplifier design too. Right now, I'd like to get more people involved in vacuum tube amplifier design before we FORGET how to do it.
I love steam locomotives and, some years back, at the Railroad Museum in Sacramento, one of the docents made a comment that caught my attention. He said "The technology and knowledge no longer exists to design and build one of these engines". I fear that the same thing is starting to occur with these old tube circuits ...
On top of that, there's not a lot written down (at least not accessibly) about tube manufacture. A lot of the source materials were either proprietary to the manufacturers or have been discarded (by libraries and former practitioners) as being no longer relevant.
I think of the whole tube amp industry as an illustration of "reverse" cargo cultism. Loosely defined, cargo cultism is the the adoption of the trappings of an advanced technology by people who don't understand the underlying principles. So reverse cargo cultism would be the adoption of the trappings of an obsolete technology by people who don't understand the underlying principles.
Thanks for the kind words. My forum participation goes in cycles, depending upon what else is going on in my life.But anyway, thanks for your note --- valid points. And please come back more often. (From reading back through all of the old posts, you used to frequent this forum regularly, not so much now )
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A lot of my arguments are semantically derived. Originally Posted by randyc
Yes, I have conflated repair with maintenance.
I'm not so sure about that. There's a difference between the magnitude of the temperature and its long-term effects.Also, the designers of the day understood thermal problems, in my opinion, BETTER than guys like me whose background is solid state design, they dealt with temperatures that far exceed anything normally experienced today.
Certainly the design and manufacturing of tubes would have benefitted from the precision manufacturing and advanced analytical techniques available today.If they would have had the same FEA tools that are available to me, who knows what they would have accomplished ?
Recently, though, I was surprised to learn that the design of high-performance motherboards for computers is based upon statistical sampling. That not only offended my engineering sensibilities, but confirmed a lot of suspicions.
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Now that starts to approach the age-old argument of predicted reliability versus practical reliability. If one were to approach the problem from the standpoint of long-established reliability calculation procedures (e.g. Military Handbook 217 and its commercial imitations), the prediction would indicate that the increase in temperature would dramatically reduce the lifetime of passive components (resistors, capacitors, inductors - if applicable). Originally Posted by TieDyedDevil
However it has to be noted that the contribution of the passive components is "mice-nuts" relative to the overall assembly or a system, for several reasons:
1. Overwhelmingly, the active components (solid state or vacuum tube) are the major contributor to reliability (or lack).
2. Combined part failure rates of ALL passive components will usually amount to MUCH less than 1% of the total part failure rate of the assembly.
3. Most passive components (electrolytic capacitors excluded) fail "gracefully". They may look burned and disfigured but power resistors, as an example, will still function as power resistors - their values will just be changed somewhat. (And good design takes that into account.)
4. There's just not much in the makeup of passive components that will follow the old rule of chemistry: "a process will usually double for every increase in temperature of 10 degrees Celsius".
5. Unfortunately, active components (tubes or solid-state) unfalteringly obey that old chemistry law. And not in a GOOD way
6. Finally .... the number of old Ampeg and Fender amplifiers out there, still functioning flawlessly, points out the inherent reliability of a proper design using safe de-rating guidelines. This DESPITE the higher temperatures experienced compared to an equivalent solid state amplifier.
I'm not a Reliability Engineer but in the course of my career (almost always Military/Aerospace), I've had to do a lot of reliability predictions, in fact I was still performing them up until a few years ago when I finally terminated my consulting business.
Performing all those calculations and designing large amounts of hardware over the past thirty years has given me a healthy amount of skepticism regarding the absolute value of predicted failure rates (MTBF) but the exercise has a deeper intrinsic purpose than to attempt a determination of how long a piece of equipment will survive ...
The "real" purpose behind using MIL-HDBK-217 is to point out those components that are most susceptible to failure and to point out the nature of the likely failure (thermal stress, voltage stress, mechanical failure, and so forth). From that aspect, I have respect for the process of reliability prediction and for the hundreds of scientists and engineers who contributed to the writing of the Handbook.
Anyway - all of that verbiage just means that the lifetime of a vacuum tube amplifier is virtually dependant upon the lifetime of the TUBES and that the substantially higher service temperatures have a minimal effect on the rest of the components, if they were properly selected in the first place.
And getting back to one of my initial premises in the vacuum tube post, I am uncertain that the modern equivalents to these old tube amplifiers are getting the same amount of attention to parts selection, derating criteria and reliability prediction as was applied to the original models. But that's just an opinion at this point - maybe one of these days, I'll get an opportunity to completely test a boutique amplifier and then crack it open to see how it's constructed and what parts are being used ....
cheers,
randyc
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Originally Posted by TieDyedDevil
I love your notion of "Betty Crocker Engineering". That's hilarious.
I tend to steer clear of self-proclaimed "experts" in "toob amp design". The truth of the matter is: it's exceedingly easy to construct a tube amp that works, and not that much more difficult to design an amp that meets certain broad behavioral goals given a knowledge of a few very simple design principles.
But most amp designers, including those who make the expensive boutique amps, seem to be doing "Betty Crocker Engineering" or "painting by numbers". Granted, their workmanship may be exemplary, but most (not all) of them are rehashing old designs with minor tweaks.
You've also alluded to the variability of tube circuitry, made even more problematic by the poor production standards of modern tubes. A lot of effort goes into tweaking one particular amp then applying those results to the broader population, with predictably unpredictable results.
I'm far more pessimistic than you. The folks who had a proper understanding of tube manufacture are already in the ground. The few who still care to manufacture tubes are simply trying to keep the old machinery and processes going as best they can. My impression, though, is that they don't have the wherewithal to proactively improve the manufacturing process, so they rely on statistical methods to try to get a more consistent yield.
On top of that, there's not a lot written down (at least not accessibly) about tube manufacture. A lot of the source materials were either proprietary to the manufacturers or have been discarded (by libraries and former practitioners) as being no longer relevant.
I think of the whole tube amp industry as an illustration of "reverse" cargo cultism. Loosely defined, cargo cultism is the the adoption of the trappings of an advanced technology by people who don't understand the underlying principles. So reverse cargo cultism would be the adoption of the trappings of an obsolete technology by people who don't understand the underlying principles.
Thanks for the kind words. My forum participation goes in cycles, depending upon what else is going on in my life.
Somehow, I missed this ENTIRE post, and it's a good one. We share the same opinions - unhappily we're in a minority. The ones that are manipulating the cults are getting rich while we're just getting smarter Oh well. Anyway, good to see you posting again !
Randy
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hmmmm, do you suppose that one could interest a venture capitalist in funding a U.S. tube startup ?
(Beam power tubes only, not the little dual triodes .... EXPENSIVE stuff.)
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If my understanding of the reasons the industry shut down in the first place (declining demand coupled with concerns about the toxic byproducts of vacuum tube manufacturing), it'd be folly to invest in a new plant for such a small market. I could be wrong... Originally Posted by randyc
hmmmm, do you suppose that one could interest a venture capitalist in funding a U.S. tube startup ?
(Beam power tubes only, not the little dual triodes .... EXPENSIVE stuff.)
FWIW, I think that Western Electric stayed in business (manufacturing high-power tubes, IIUC) for quite a while after everyone else had closed their doors in the USA. According to a quick Google search (again, I may have missed something), even Western Electric seems to no longer manufacture tubes in the USA.
Groove Tubes makes a big deal about their "US-made" 6L6s, but I thought I read that they're not entirely manufactured in the USA.
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LOL, that wasn't a serious suggestion.
The design knowledge might still exist, the manufacturing techniques could probably be recreated but the materials engineering ... ???
Western Electric triodes are highly valued, I believe, by audiophiles, using them in inefficient Class "A" audio amplifiers. (As far as "Groove Tubes" are concerned, if they do anything that might be loosely construed as "manufacturing" I'd suggest that it might be, for example, inserting the imported tubes into their own proprietary boxes.)
SOME very high power vacuum tubes are still being used, no idea where they are manufactured. They are special purpose devices used for powering multi-kilowatt transducers like the ones used in shock/vibration tables in large environmental labs. Maybe there are a few around in broadcast radio transmitters ... dunno where they might be manufactured either. But both of those applications are transitioning (with the advent of Class D techniques and larger VMOSFET structures) ...
As an example of how things have changed, a couple of years ago, I designed/built several high voltage power supplies that normally would have required the use of tubes - ten or fifteen years ago, I wouldn't have even considered using transistors. Now, 1000 volt MOSFETs are readily available for a couple of dollars U.S. and that's what I used.
Thanks for the info !
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I just spent a productive and satisfactory afternoon and evening, first, watching the drummer son a good friend play with his friends (the oldest is not old enough to purchase alcohol in our state) at some sort of benefit at a local pub. I was astonished (disregarding the fact that they played 'way too loud and fast) at the musicianship and familiarity with their instruments they exhibited, and, more to the point, the fact that there was not a vacuum tube in sight.
Later, my good friend and I gathered our resources in my living room, with an invited guest in the form of another member of our congregation, who will join us at our church as part of our "Baptist Blues Band." I played my 335 through the Jazzmaster Ultralight, and, in passing, noted that I would take the Blues Jr to the church tomorrow.
"Don't do it! Take the JM!" Such was the spontaneous response from the others.
It's not about the circuits, it's about the resulting sound.
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John:
No doubt, no doubt - the sound is all. I have three solid-state amplifiers and five vacuum tube amplifiers ... when any of them is properly adjusted for a specific guitar, they are equable to my ears. But that's probably more due to the type of music that I play now as opposed to the music that I played when I purchased some of those tube amplifiers.
My absolute "best" (to me) amplifier is an ultra clean (0.25% distortion at 100 watts - that's about TWENTY times "cleaner" than a Twin) Sunn Beta Lead, that I bought new in 1982. It is truly a high-fidelity amplifier in every sense of the term. After I bought it, I retired the thing after a couple of gigs and went back to the Fender Bassman, through a single 12 speaker. (One small PART of that decision was due to the weight of the Sunn, about ten pounds heavier than my Twin !)
My lack of happiness with the sound had everything to do with the squeaky cleanliness of the Sunn. The material I was playing at the time just didn't lend itself to being reproduced by that amplifier. At this point in my declining musical experience, the Sunn is the best of the best ... it's usage is limited to one room of my house because I don't want to move it. But it used to live in the living room, so that I could play it daily.
When I was given an Epiphone Galaxie (the one described in the original post) I parked it in a convenient niche in my living room where it is completely invisible. I use it because of that reason rather than a preference for its vacuum tube sound. (It is a nice amplifier though, it's also squeaky clean ... at least for a TUBE amplifier.)
Cheers John and thanks for the CD - got it today !
RandyLast edited by randyc; 11-14-2009 at 10:24 PM.
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Absolutely! When I think about it, I'm a bit disheartened that people of my generation are largely responsible for promoting the somewhat ignorant (in that the vast majority of its proponents seem either unwilling or unable to have an informed and qualified viewpoint) pro-tube fervor that drives cynical marketers to cash in by selling gear that uses junk components, poor designs and even "ornamental" tubes. Originally Posted by lpdeluxe
On the plus side, the tide does seem to be turning. People are starting to realize that "modeler" is not synonymous with "POD" and that Line6, which created the market segment, has long since ceased to be a leader in terms of innovation or quality.
Notice that both Harmony Central and The Gear Page now have sections devoted to players who incorporate non-traditional technologies into their guitar rigs. No matter where you look, there's still the usual elitist nonsense ("the most expensive must necessarily be the best in all regards"), but even that is changing amongst certain groups.
Sorry about the lengthy off-topic post...
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