Should I change out original 41 year old screen grid resistors on a 1984 Marshall?

  • Thread starter Thread starter harddriver
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harddriver

Well-known member
I don't see signs of excessive heat and they both test fine...984ohms and 976ohms....I know these things take some abuse over time.

I have new Welwyns's here ready to go....I figured since I am already into this amp rebuilding it....why not???????????

Should I go with the if it's not broke adage or just install some new ones for peace of mind?
 
dead-pan said:
Measure them.

I had a single tube take out one. The amp sounded fine. So....
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Exactly. My 71 JMP didn't need changed, but I did the signal caps and a few other from my stash. That 50w is a beast.
 
Why create more work if they are not fried. I'd wait till I was at least doing a retube of the power section.
 
I'm assuming 1984 means you're likely dealing with a 2203/2204 instead of a Superlead. Those resistors don't get worked too hard unless the amp is played wide open. I'd leave them alone. The don't normally wear out. I've seen plenty of them get hot enough to flake off the coating but they still read fine. Cement wirewound resistors handle heat the best. If I replace them, that's usually what I'm going for unless I'm doing a period correct restoration on something much older.
 
Purgasound said:
I'm assuming 1984 means you're likely dealing with a 2203/2204 instead of a Superlead. Those resistors don't get worked too hard unless the amp is played wide open. I'd leave them alone. The don't normally wear out. I've seen plenty of them get hot enough to flake off the coating but they still read fine. Cement wirewound resistors handle heat the best. If I replace them, that's usually what I'm going for unless I'm doing a period correct restoration on something much older.
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Yeah it's a 2204. The screen grid resistors are still the stock black ERG brand ones Marshall used in the 80's. I wasn't sure if screen grid resistors could develop an intermittent failure due to chronic heat generation over the 41 year lifespan.

Thanks for all the replies! I appreciate the feedback!:2thumbsup:

I just wanted to see what the consensus was since I was getting ready to start final assembly on this amp I thought now was the time to thrown them in if I should.
 
harddriver said:
Yeah it's a 2204. The screen grid resistors are still the stock black ERG brand ones Marshall used in the 80's. I wasn't sure if screen grid resistors could develop an intermittent failure due to chronic heat generation over the 41 year lifespan.

Thanks for all the replies! I appreciate the feedback!:2thumbsup:

I just wanted to see what the consensus was since I was getting ready to start final assembly on this amp I thought now was the time to thrown them in if I should.
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Then that changes things. If you're in the middle of a rebuild, repair, or mod to the amp, then fuck it and replace them with new ones since you're already working on it.
 
I’d only replace them if they looked compromised, measured wrong, or I was replacing the sockets. Some of those power tube sockets around that time have a sort of ‘blade’ connection…and kind of suck. Very difficult to re-tension and they can flop to the side and not grab the pin.
 
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