No gain lotta pain

  • Thread starter Thread starter Dougtech
  • Start date Start date
If you post gut shots maybe we could spot something.
 
A '78 that hasn't had the caps replaced?Duuuuude, please get that amp to a tech right away. I wouldn't even turn it on anymore. Ask around and find a tech that really knows what they're doing. A bad cap can explode. It happened to Dave Friedman and he said he had to clean the inside of that amp several times to get all the residue out of there. Let the tech (a tech who knows old Marshalls) get in there and see what's going on in the amp. That amp should sound magnificent after it's been recapped and repaired. Good luck!
 
JohnnyGtar said:
A '78 that hasn't had the caps replaced?Duuuuude, please get that amp to a tech right away. I wouldn't even turn it on anymore. Ask around and find a tech that really knows what they're doing. A bad cap can explode. It happened to Dave Friedman and he said he had to clean the inside of that amp several times to get all the residue out of there. Let the tech (a tech who knows old Marshalls) get in there and see what's going on in the amp. That amp should sound magnificent after it's been recapped and repaired. Good luck!
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Thanks, so far I cannot find an amp repair company near me. Don't really want to send it anywhere.
 
Dougtech said:
Thanks, so far I cannot find an amp repair company near me. Don't really want to send it anywhere.
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If you finally decide to send it out, send it to Dave Friedmann. Besides Friedman amps, Dave is the amp and rack guru to the stars. His company's name is Rack Systems. He's in Los Angeles. He was Eddie Van Halen's guy. He rebuilt Ed's original Marshall, the one on the first 8 Van albums. I've been to his workshop a few times and heard the amps he's worked on. Effin' amazing sounds come out of those amps after he's worked his magic on them. Can't do better than Dave Friedman for working on Marshalls in my humble opinion.
 
Some pics would help as a ton of them were modded. Maybe some resistor values drifted up or theirs some weirdness with the gain pot, maybe try wiggling it around to see if it cuts in and out or crackles.
Is there any change in volume or sound between the low and high input? And have you played other master volume Marshall’s? They don’t have very much gain.
 
Just to echo what’s been said before there are two factors going on.

The first involves the large caps sticking out of the chassis. Those are filter caps that help turn AC to DC for the tubes. If they go bad, they can take out the power transformer by acting as a short circuit for far too long during initial turn on.

The second problem is in the preamp regarding no gain. I personally feel like it’s a bad potentiometer since you said it would come and go.

Have your tech go over it top to bottom. It needs a full recap of all filter caps and bias caps (10uF x2, not 8uF x2)

I’d suggest a full retube as well if you haven’t replaced the tubes
 
Dougtech said:
Thanks, so far I cannot find an amp repair company near me. Don't really want to send it anywhere.
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What do you consider "near" you? There are competent reputable people in Michigan, but that covers a lot of area

glpg80 said:
Just to echo what’s been said before there are two factors going on.

The first involves the large caps sticking out of the chassis. Those are filter caps that help turn AC to DC for the tubes. If they go bad, they can take out the power transformer by acting as a short circuit for far too long during initial turn on.

The second problem is in the preamp regarding no gain. I personally feel like it’s a bad potentiometer since you said it would come and go.

Have your tech go over it top to bottom. It needs a full recap of all filter caps and bias caps (10uF x2, not 8uF x2)

I’d suggest a full retube as well if you haven’t replaced the tubes
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I'll add the caveat that *if* the electrolytics have not been changed, then that's good maintenance.
The problem sounds like it could be a few things; ... bad pot, tube socket, tube itself, connections, etc. Good photos would help.
The description sounds like the amp is a 2204, not a nuclear reactor ffs.


PLX said:
Try putting a UD-50 in front.
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If you have contact cleaner, or Deoxit I'd try to clean the pots.....you spray it into the small opening that you can see by the lugs(where the wires are soldered) and once you spray it turn the knob back n forth, over and over. The preamp pot might be super dirty and needs a good cleaning. That's gonna be the cheapest and easiest fix IF it's the problem....if you don't have either head to a hardware store and they should at least have contact cleaner.
Good luck.
 
Just get a drive pedal with a decent amount of gain. Nothing beats an old master volume JMP with an SD-1
 
There are some very knowledgeable members here who are capable of magical circuitry, state your location and maybe a member is near you. One of rigtalks lords of amp building and circuitry magic is close to me. Perhaps it will be the same for you.
 
Racerxrated said:
If you have contact cleaner, or Deoxit I'd try to clean the pots.....you spray it into the small opening that you can see by the lugs(where the wires are soldered) and once you spray it turn the knob back n forth, over and over. The preamp pot might be super dirty and needs a good cleaning. That's gonna be the cheapest and easiest fix IF it's the problem....if you don't have either head to a hardware store and they should at least have contact cleaner.
Good luck.
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Thank you very much. I cleaned the pots as you recommended and the grit is back. It has not gone away so far. I feel confident that that was the cure. Hope you had a great weekend.
 
Dougtech said:
Thank you very much. I cleaned the pots as you recommended and the grit is back. It has not gone away so far. I feel confident that that was the cure. Hope you had a great weekend.
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Glad my suspicion was right and all is well. You should still have a tech replace the gain potentiometer. Those old carbon traces do wear over time.
 
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