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I have a SuperChamp XD about 5-6 years old. It has performed flawlessly until recently. It has 2 6V6GTs and a 12AX7 tubes.
The other night we were playing our monthly cigar bar gig, and the amp sounded horrible—shrill, no power—cranked up to 8 on the clean channel, and the strings sounded unbalanced or out of phase. I am assuming it is a bad tube, but haven’t had a chance to check it yet.
I am familiar with how to check to see if a tube is bad, but I have also heard some tubes look OK but are bad. I don’t know of a place that has a tube tester near me, so I was thinking of replacing all the tubes at once.
A couple of points/questions: 1) would you have any qualms about replacing tubes yourself? Most websites say turn off for 20-30” and leave one hand in your pocket to prevent completing a voltage circuit. My BIL played a Twin Reverb back in the 60’s and said he would just remove and plug in the tubes without any precautions back in the day. And he’s still here LOL. (He has his original 1965 Gibson 335T for sale on consignment at Willie’s in case you’re interested...asking $8000 IIRC.)
2) If you replace, would you use same tubes or upgrade? I think these tubes are OK for jazz. I was looking at JJs, since I think they are OEM.
3) Do you need to bias if you replace with the same tubes? What about different tubes? I have to admit the biasing part spooks me quite a bit. I play around with tools of all kinds but electricity scares me.
Thanks in advance for the advice.
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06-09-2019 09:05 AM
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I worked in my father's radio/TV repair shop through high school and college, and we changed thousands of tubes, in all sorts of devices. You can almost never tell if a tube is bad by looking at it. Tubes show internal darkening naturally while still working fine, and they can go bad and still look brand new. To change one (or more) just pull the old one out and put the new one in. We never bothered with waiting for anything, because time is money. We didn't even always turn the device off. I suggest unplugging the amp before changing the tubes, just because you're unfamiliar with doing it, but nothing else needs to be done. Most amps have the components inside the chassis and the tubes on the opposite side, so you're not going to touch anything dangerous while changing tubes. No need to pull the chassis out of the amp, just do it by feel. Replace with the same tubes and don't worry about biasing. You don't have the test equipment or knowledge, and it really doesn't make that much difference. I don't know about that specific amp, and it may be self biasing, dunno, but either way don't worry about it.
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The advice of putting one hand in your pocket should be followed. You can get a fatal shock from the capaicitors in a tube amp. You cannot be too careful.
The preamp tube is likely not the problem, but swapping these out can influence the tone particulatlt is you find some NOS tubes or try swapping the stock tube with a 5751.
One or both of your 6V6’s is the likely culprit. I replace mine annually. I prefer JJ’s.
HTH.
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I have been a electronics technician for 39 years.
The best way to replace tubes is with a solid state amplifier.
I did it years ago and I am not a bit sorry.
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+1 Tubes became obsolete long ago. Solid state is cheaper, lighter, more reliable, and sounds at least as good. I have a Fender tube amp, and it just takes up space. I never use it unless I need a space heater in the winter. It works well for that.
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I changed tubes and biased my SCXD a couple times in the last few years and it wasn't that big of a project. There's little danger in changing tubes, it's biasing the amp while it's powered up that needs the caution. The SCXD has a bias pot, which is really sweet, cuz most 6v6 amps don't have one and only a tech would have the gear to bias it. Using reliably matched 6v6 tubes is important.
This info will give you an idea.
How to Bias a Fender Super Champ XD (SCXD) | Fender Stratocaster Guitar Forum
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Thanks for the replies. You answered a lot of questions.
LOL.
Originally Posted by BBGuitar
I have 2 SS amps as well, I just like the models and effects of the SCXD. I also appreciate the extra tube warmth, but I might be biased. ;-)
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Hey, it works for you, as it did for BB King. Anybody wanna challenge THAT tone? Originally Posted by BBGuitar
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I remember that blue flame in one of the power tubes acting like a little demon.
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1) would you have any qualms about replacing tubes yourself?
No. If you can plug in a cord to a wall socket, you can change a tube. Back in the day, everyone did it all the time with TV sets.2) If you replace, would you use same tubes or upgrade?
This is a tone question. Just make sure the voltages match. Like don't replace an EL34 with a 6L6, you won't like what happens when you hit the power!3) Do you need to bias if you replace with the same tubes? What about different tubes?
With most amps, yes and yes. Mesa Boogie amps have the self-biasing feature with matched tubes, but I think that it's good to bias those also. This is also a user-capable job--pretty simple with the right tools, google it.Like was mentioned before--plenty enough voltage in there to kill you several times--so be careful!
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I have no qualms about changing tubes myself; have done it countless times. You should wait a few minutes after turning off the amp so the tubes can cool down. Yes, unplug it, but the warning about keeping your hand in your pocket has to do with opening up the amp chassis to work on it, not changing tubes. The only caveat I have about this is that you're assuming the tubes are the problem, when it might be something else. You can try changing the tubes, and maybe the problem will go away (and hence rule out other problems), but you might wind up needing the have the amps serviced. Noises, buzzes, changing in loudness, etc. are often caused by other components. Originally Posted by Doctor Jeff
From what I understand about the Super Champ XD, the tone is shaped mainly by the DSP, so I doubt you're going to see a lot of benefit from more expensive tubes. Maybe if you play it cranked loud enough for power section distortion it'll make more of a difference, but I wouldn't invest a whole lot of $'s or thought into tubes for that particular amp. Originally Posted by Doctor Jeff
- It's generally a good idea to re-bias the amp when you change tubes, but it is not strictly necessary. Biasing helps optimize the amp's performance, but nothing terrible will happen if you don't do this. Originally Posted by Doctor Jeff
- If you use literally identical tubes (as in tested and matched to be identical to what was there before, with the certainty that the amp was correctly biased before), the same bias settings will be correct for the new tubes. Otherwise, though, the "same" tubes are rarely actually truly the same because of tolerances in the way tubes are made. As I said before, if you don't bias, the world will not end, kittens will not die, etc. But you can't really count on the tubes themselves obviating the need/value of biasing.
- Unless you have the proper equipment and skills, don't try to bias the amp yourself; take it to a tech for servicing. There are tools that make it somewhat easier and eliminate the need for an oscilloscope, but you still need to know what you're doing. The advantage of doing that is that the tech will check out the amp and fix what ails it aside from just changing tubes.
FWIW, I don't try to service amps beyond the most basic stuff (e.g., changing tubes, replacing a broken plug). When my amp starts to misbehave, I take it to a tech for an overhaul, and accept his recommendations about what tubes to use.
John
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My 2 cents. I have an SCX2 which is the next generation of the XD. The tubes go bad for sure. You can replace them easily enough, but you should use the same type of tubes on this particular amp. With other amps you can swap out different pre-amp tubes, but these amps don't have pre-amp tubes per se. The small tube is a phase inverter tube and should be the same type as stock. You can get a better tube amp sound by using a separate tube pre-amp. I use one of these and a hemp speaker from Weber.
Access to this page has been denied.
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Well .... BB sounded MUCH better through tube amps. I saw him many times, starting in the late 70s, using everything from the Lab Series SS amps, tweed, BF, and SF Fenders. BB through a tweed Twin is THE classic sound. That's what he used on Live at the Regal. Live at Cook County Jail is a SF Twin. His Lab Series tone can't touch that. Originally Posted by dickbanks
JohnLast edited by John A.; 06-10-2019 at 05:53 PM.
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I don't know high scientific it is, but I find tube amps to be less fatiguing than SS amps when listening/playing over long periods of time.
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If the amp has an adjustment potentiometer you might use a bias probe, like this:
That one has two pass through connectors that plug into the tube sockets and then you plug the tubes into the connectors. They provide the path to your meter through the red and black plugs. There are versions that have just one connector, two connectors, and four connectors, and other differences of switching convenience (some have the meter built in). The black box on mine has two switches so I can independently select which tube I'm measuring and whether I'm measuring plate voltage or cathode current.
You need to know the max heat dissipation spec of your tubes, make voltage and current measures, then put those values in an equation that will inform you of how much of the tube's heat dissipation limit is being consumed (a "not to exceed" percentage value you have already chosen). Then you measure, calculate, adjust, remeasure, recalculate, readjust... and using a bias probe allows you to play the guitar and hear how it sounds while you are going through the adjustment process. When it sounds the way you like it while still within the dissipation value you choose not to exceed, you turn off, wait a bit, remove the connectors and put the tubes in directly.
I have seven Fender tube amps and I've used my bias probe dozens of times over the years; was about $30 back then.
It is not required to understand the electronics, but it is absolutely critical to follow the specific instructions for your version of bias probe, because mine, for example, measures the tube cathode current (Ik) and plate voltage (Vp) as DC voltages by indirectly measuring the cathode current using a 1 ohm resistor (so the meter displays the reading in mV, and 1mV represents 1mA of tube cathode current) and using a 10Meg ohm resistor network to drop the plate voltage measure by a factor of 1,000. Different bias probes use different ways to convert the source values to reading on the meter, so instructions are critical to doing it right (you have to use the correct values in your adjustment equation calculations).
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Originally Posted by sgosnell
they still make tube amps, but you probably know that.
I'll be using my blackface Twins and Vibroluxes until I die or my arm falls off, whichever comes first.
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I'm pretty sure they still make buggy whips, too. And vinyl LP records. There is a niche market for almost anything.
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I still listen to vinyl albums but can't say I've bought a buggy whip in awhile.
oh well, just call me Mr. Niche I guess...
just having fun, whatever floats one's boat is cool w/me.
but I love my old anvils, and I'm getting a workout when I'm working.
better than laying on a bench w/barbells....
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Different manufacturer's tubes have very different sounds. I stumbled onto the Watford Valves site some years ago, and their Reports section includes some very detailed reviews on the behaviour and sounds of these different tubes. I found it invaluable when I last did a full retube of my Princeton Recording
Here's a link
Watford Valves :: Reports
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My neighbor for many years was Ron Levy. He grew up playing B3 & Piano for BB (he was 16 at the time!). He said he was the "token white kid". He also plays on BB's Live at Cook County Jail Album. When we were neighbors his now ex-wife was a co-founder of Rounder Records (George Thorogood) When Rounder started their Black Top Blues Label Ron became the labels House Producer and moved down south. Our houses were less than 7 feet apart so I would listen to him play his B3 for hours and jam along from my house, when he wasn't on the road. One day, before they broke big, he had the original Fabulous Thunderbird's over for a jam session in the back yard! They started out on Rounder Records. Good times. I wish I was more under control back then. I was way too wild to have taken advantages of the many opportunities that were offered to me. At least I changed and I'm still here. Originally Posted by John A.
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Cool! I'm a few more degrees of separation from authentic blues greatness than that, alas. I think the closest I've come is jamming with a guy in Washington Square Park who claimed to be Jimmy Reed, but wasn't. Anyway, I started getting into blues at a time when there were still a lot of places in NY to hear the real thing, and many of the early Delta and first generation electric blues guys were still around. So I was fortunate to have seen many of these folks up close (though I only saw BB in bigger venues). Originally Posted by Strbender
John
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I'll add my Vinyl record collection, turntables, and audiophile tube amps/preamps to that list. Tube amps and audio amps rule! Originally Posted by wintermoon
they still make tube amps, but you probably know that.
I'll be using my blackface Twins and Vibroluxes until I die or my arm falls off, whichever comes first.
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Replacing tubes is not a big deal. Buy a set and wiggle out the old ones, then wiggle in the new ones. Seriously.
You will not get shocked or killed or whatever.
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Tubes get nice and warm. FETs just sit there and stare at you across the bar, ice cold.... Originally Posted by lammie200
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Beware of not touching forbidden parts when you swap tubes, otherwise :
And then :
Fortunately (or not ?) never happened to me
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