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Post subject: Some issues with 1970(?) Bassman 4x10
Posted: Thu Oct 01, 2009 8:15 pm
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Hey all, I was wondering if any of you nice knowledgeable people could help me out with a little problem i'm having.

I have a 1970 or so Bassman 4x10. It's in need of a fix but i'm not sure what the problem is.

What happens is every few seconds or minutes I get this crackling sound, and also there is a periodic fluctuation in volume and tone.

It has nothing to do with the cords or jacks because even with no guitar plugged in I can still here the crackling.

It's worth noting that one of the speakers is kind of busted, and also the power cord covering is kind of splitting at the end near the plug itself, could it not be getting a steady stream of power?


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Posted: Thu Oct 01, 2009 8:28 pm
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If you haven't ever had the electrolytic caps replaced, you should. Bad filter caps can be pretty noisy. They may be over 30 years old. I'd check the tubes too. It's probably due for some routine maintenance.


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Posted: Thu Oct 01, 2009 8:30 pm
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63supro wrote:
If you haven't ever had the electrolytic caps replaced, you should. Bad filter caps can be pretty noisy. They may be over 30 years old. I'd check the tubes too. It's probably due for some routine maintenance.


Well the tubes are pretty fresh. But the electrolytic caps I don't know, i'm sure they are fairly old like you said. Would they cause the fluctuations in volume and tone?


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Posted: Thu Oct 01, 2009 8:37 pm
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63supro wrote:
If you haven't ever had the electrolytic caps replaced, you should. Bad filter caps can be pretty noisy. They may be over 30 years old. I'd check the tubes too. It's probably due for some routine maintenance.


Well the tubes are pretty fresh. But the electrolytic caps I don't know, i'm sure they are fairly old like you said. Would they cause the fluctuations in volume and tone?


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Posted: Thu Oct 01, 2009 9:51 pm
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My first suspect would be a faulty tube or oxidized tube socket, next would be dirty pots. Does the fluctuation occur after the crackling? and does movement of the amp cause the problem? IMHO electrolytic caps won't exhibit intermittent signal loss, but if they are over thirty years old, I think it's time. Coupling caps on the other hand can cause signal loss if they leak DC and will goof up the bias of the next stage. I'd go with Supro's advise of a routine maintenance check up at your local amp clinic. ART

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Posted: Thu Oct 01, 2009 9:59 pm
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aclempoppi wrote:
My first suspect would be a faulty tube or oxidized tube socket, next would be dirty pots. Does the fluctuation occur after the crackling? and does movement of the amp cause the problem? IMHO electrolytic caps won't exhibit intermittent signal loss, but if they are over thirty years old, I think it's time. Coupling caps on the other hand can cause signal loss if they leak DC and will goof up the bias of the next stage. I'd go with Supro's advise of a routine maintenance check up at your local amp clinic. ART


I don't believe the fluctuation necessarily happens after the crackle, it seems pretty random to me, but i'll try to pay closer attention.

Thanks for the help.

I'll check to see if I can narrow it down based on your input.


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Posted: Sun Nov 01, 2009 4:06 pm
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had a similar issue with my Bandmaster after caps were replaced. Turned out to be a bad input jack and pot on the Normal channel. Replaced, and now the amp is dead quiet with nothing plugged in and on, or with guitars in but not being played - perfect.


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