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Hi,
My 1966 DR is cutting in and out on both channels. First thought: New tubes? If so, where do you recommend I get them? Or might it be another problem? I would appreciate your thoughts. I have learned a lot here over the years. Thank you for any assistance.
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06-29-2024 08:00 PM
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I'm not an expert and nobody should believe anything I say about this. Except, believe this: there is voltage in the caps even after the amp is turned off and unplugged. So, if you don't know what you're doing, you could do something dangerous.
Originally Posted by Phil59
Caveats aside, I would suggest gently wiggling and pressing things to see if you can reproduce the crackling. That would include the speaker leads, the face plate, reseating the tubes, pressing and wiggling the connections to the reverb tank, wiggling the input jack (gently) and anything else pressable or wiggleable. I'd also suggest looking at the tubes when the amp is on and seeing if any of them look funny. Power cable? If the pilot light doesn't flicker, it's probably not that.
If you're pressing a metal part, consider doing it with something made of a non conductive material, like a drumstick or chopstick. Plug the amp into a powerstrip with a switch and make sure you can reach the switch instantly. Please don't ask me how I know that.
Others may advise swapping identical tubes in different positions and seeing if that makes a difference.
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90% of a tube amps issues are tube related.
Check to see that the power tubes are glowing normally, and not red plating.
Make sure the rectifier is glowing as well.
Unless it's a bad transformer it's probably a tube since you're having issues w both channels.
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If its cutting in and out on both channels then its something common to both channels and probably not signal tubes. Id suggest possibly power supply related id check the rectifier tube first. The cautions regarding high voltage are not to be ignored. Replacement tubes these days are a crap shoot the old European stocks are nearly depleted and Chinese tubes are inconsistent even from the same manufacturer. See if you can find an old radio guy they know tube amp power supplies and would have sources for decent tubes. Good luck
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back when..had several Twin Rev ,, they were played alot and sometime hard..not one tube problem..
Now this was a very different time..and you could find quality parts for amps and have a tech that knew about them
all for a price you could afford.
My Blues Jr with a Lansing speaker had a tube problem within one year. It was expensive and the local shop had to
"send it out"..to god knows where.
Now looking for a SS..and there are many today that come close-if not equal to that tube sound - at half the weight.
Long gone are the purist ideas of "the good ol' days".. hell to that..there are car guys that still swear by carburetors..
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I've been buying from eurotubes.com for years & can recommend them wholeheartedly. I have had great performance from the JJ tubes. The owner is knowledgeable and helpful, prices are good, delivery is fast and quality is first-rate.
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I think this might be a "take it to the tech" situation.
There's a couple of simple things that you could look for, but since it happens on both channels, I suspect it is not a preamp tube; a power amp tube or rectifier tube might be a possibility. But I think it's more likely there is a failing capacitor/resistor or a failed solder joint somewhere in the power amp circuitry. Although a lot of these problems cause crackles and pops, hums and buzzes, volume changes, frying bacon noise, etc., rather than just cutting in and out.
Simple things to check for: tubes that are loose in their sockets; a speaker wire that is not solidly connected to the terminals on the speaker or to the circuit board (on my amps, that is via a quarter inch jack inside the amp, but I don't know about yours). You could unplug the tubes and plug them back in a few times to clean off the pins and sockets; you could even use a contact cleaner to do this such as DeOxit.
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Check the simple things first, then take it to a tech.
The simple things are:
use a different guitar cable, one you know is good.
check the speaker wire
try a new phase inverter tube. That’s the little one next to the power tubes. It’s part of the power amp and everything goes through it before it reaches the power tubes.
try new power tubes.
try a new rectifier.
Come to think of it, just take it to a tech. He’ll have all those things on hand and can go through it quickly.
But try a new cable first.
It’s very likely something like a bad solder joint. You didn’t say if this was new or vintage. New amps are wave-soldered PCBs, and cold joints happen. On vintage amps, joints can deteriorate; filter caps can deteriorate, lots of things can happen. The board can go conductive. Sockets can corrode or have to be retensioned.
Don’t open the amp and start poking around. I’m guessing electronics isn’t one of your hobbies. A tube amp with 400v isn’t a battery-powered transistor radio.
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"You didn’t say if this was new or vintage."
If it's a '66 as he posted it's not a reissue but checking the cable is a good idea, I thought he would have tried that.
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I would try a different cable, a different speaker and different tubes. If that did not solve the problem, I would take it to a tech.
Getting electrocuted is not worth the savings of trying to fix it yourself.
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You can develop a list of potential causes from the information you haven't provided. "Cut out" is a vague term that has to be defined much more fully. Does the output simply shut down, or does it fade in and/or out? Is the output completely gone or is it still faintly there? How long does it typically last, and is it consistent or widely varying in duration? How often does it happen? Does it happen with more than one guitar and more than one cord? Are there any extraneous noises before, during or after a dropout? If so, what are they - crackle, buzz, hum, hiss, pop, click, other? Is the volume stable until it cuts off, and is it normal immediately on coming back in? Have you had to set your volume pot higher or lower than you used to do to get the same playing volume when it's working?
Check the fuse. Every once in a while, the fuse wire will break if the amp is bumped - but the ends will remain in physical contact. Take it out and flick your finger against it firmly. If the fuse is bad, the wire in it will separate and you'll see space between the ends inside the glass. You should have spares anyway, so putting in a new one isn't a bad idea if the original one is still in it. Look at the tubes. Is there a heavy coating inside the top of one? Tap the tubes one by one with a chopstick or pencil while it's on and you're playing a chord - does the amp make noise through the speaker, cut out, or change sound quality in any way? Does the pilot light go out or change intensity when the sound cuts off? If you have another speaker cabinet, disconnect the internal speaker and plug the external cab into the main speaker out jack to see if the problem is still there. Switch the internal speaker wire plug to the external cab jack.
You can usually come up with at least a few reasonable explanations from the questions you ask and the observations you make.
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Agreed, and I will ad that in my experience (with my '66 DR), cutting in and out quickly is less likely to be a tube, and more likely to be a connection. That can be corroded tube sockets, or reverb sends, though that may be just one channel, the most likely culprit is a bd speaker connection, either corrosion in the jack or loose connector on the speaker. That's what I'd check first. Originally Posted by nevershouldhavesoldit
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I replaced mine with a LoudBox Mini.
I like it a whole lot more. Not a bit sorry.
When mine quit Fishman repaired/replaced it for $50, Can't buy very many tubes for that.
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It's not the cable. It's not the guitar. Or the fuse. I will check the tubes more thoroughly. But I will probably bring it to a tech. Two good ones to choose from. One close, with a long wait. The other 40 miles away, shorter wait. Thank you all for your replies.
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What a helpful post Originally Posted by BBGuitar
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Phil, make sure to follow up on your thread once you get it checked. Originally Posted by Phil59
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I still swear by Twin Reverbs and carbureted engines. I know lots of area gigging guitar players so I know the better techs around because everyone gets in a gear bind at some point and has gigs to do. I have the best tech I've ever known lately. The former radio repair dudes generally know their stuff and usually get off on repairing vintage tube gear. It's some kind of joy to them. Originally Posted by wolflen
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I love the sound of this particular 1966 Fender Deluxe Reverb with the original speakers. Nothing else has matched it. Originally Posted by DawgBone
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I have no doubt it is an excellent sounding amplifier. It would definitely be worth it to find a good quality tech to handle the repair. I know this stuff can be exceedingly frustrating, I've been through it a few times with older amps, but what you have there is an amp that is nearly infinitely repairable and is many times the quality of anything new you could buy for sane prices. Not sure what your general location is but if you are in central Texas I can definitely give you the name of an excellent amp tech who does reasonably priced work. Originally Posted by Phil59
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Thanks, DawgBone. I am in Virginia. As I said in an earlier post, "I will probably bring it to a tech. Two good ones to choose from. One close, with a long wait. The other 40 miles away, shorter wait."
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Pull out V6, the phase inverter and swap it with V3(reverb tube) if the quits cutting out but the reverb is flakey, then V6 was the problem. Replace V6 with a new JJ Tesla 12AT7. Both V3 and V6 are 12AT7 tubes. Also check to see the the rectifier V9 , and the output tubes V7 and 8 are tight in their sockets, as the socket pins can get loose. Also check the speaker jack and connector, and the little connectors on the speaker wires.
An easy way to drain off the high voltage is to have your guitar plugged in and strum a chord continuously while shutting off the main power switch (leave standby on) Keep playing until the sound dies and unplug the amp. This drains the high voltage caps.
Tube Depot is having regular sales and you can get a full set of JJ Tesla tubes ( matched outputs) with all six pre-amps and rectifier tubes for your DR for around $179.
Failing that, don't overlook a tarnished guitar cable plug, or speaker cable plug; clean up the plugs with some Scotchbrite and try it again.
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My vote is a intermittent/failing power or standby switch.
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Without answers to my questions in post #11, we're still in the SWAG stage. Simply changing parts in a blind attempt to fix the problem with nothing more to go on than that it's "cutting in and out on both channels" requires pure luck to succeed. Luck, like hope, is not a plan. You need to take an organized, systematic approach to figuring out what's wrong. This is the only way to find the problem in the shortest time and fix it at the lowest cost with the least effort.
Randall Smith (the Mesa Boogie guy) and a friend opened Prune Music in San Francisco before he started Mesa. His forte was diagnosing and fixing tube amps, and he was so good at it that he charged by the minute. IIRC, he charged nothing if it took him more than 10 minutes to find the problem. None of this is complicated if you identify the important factors that define the problem. Phil59, if you can provide the answers to my questions (and add any similar observations you make), it'll be a lot easier to narrow down the cause.
We still don't know how often the intermittent outages occur, how long they last, if loss and return of output are gradual (as though a tube were warming up) or sudden (which would suggest an intermittent connection in the signal chain), if there's any associated extraneous noise like a pop or static, and if it happens whether or not a guitar is plugged into the input. If this happens more often than every few minutes, it's worth just turning it on and sitting next to it with the volume high to see if the background hiss etc cuts out with no input.
If the output fades in and out, there's one cause that's not common but is well known and not surprising in a 60 year old amp. The heater winding in the power transformer can fail. Intermittent loss of output with good tubes and intact hardware throughout the signal chain (cables, connectors, etc) can be caused by oxidized or otherwise deteriorated PT windings. If the heater winding is intermittent, the tubes cannot conduct when the heaters (aka filaments) are not getting power. IIRC, the pilot light is powered by the same winding on an AB763, so it would be going on and off along with the output. If the piot light is mirroring the on - off status of the output, it's almost certainly the heater winding in the PT. The resistance of the heater winding should measure 10 Ohms or less, and the voltage across the tube heaters should be 6.2 or 6.3 volts. If it's below 6, the winding is probably bad. The way to confirm that this is the cause of the dropouts is to connect a voltmeter across the filament pins on any tube and watch it when the output drops. If the heater voltage drops too, that's your most likely diagnosis in combination with voltage below normal and resistance above normal in the winding.
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I appreciate your thoughts. But to be clear, this is way beyond my skill or interest. I discussed my plan in post #14.
Originally Posted by nevershouldhavesoldit
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Originally Posted by Phil59
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