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How do i know when to replace tubes?


bowser
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ok, I have a 1980 pro reverb that is giving me some odd sounds lately. whenever i play with the bass even at like 3 it sounds its shaking the house (you know, big and fuzzy sounding) rather than nice and clean like it has been. This happens when I'm not using any effects, and there isn't a gain knob on the amp (only turning the channel volume up all the way). I never take the master volume above 3 because it doesn't leave my room, and before I got it a 1.5 years ago my grandpa only used it for playing his accordian and his keyboard. I doubt he replaced the tubes on it and i haven't either. What could the problem be? And if it isn't the tubes, how do I know when to replace them anyways?

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take your amp to a technician. You're amp definately need new tubes. You can swamp tubes, but to have the amp working properly, you'll have to set it's bias.

Do NOT, I repeat, do NOT open your amp yourself. Some parts can be lethal when you touch them.

Don't know if this site still works, but here's alot of info on tubes and amps.

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are the tubes whats causing the problem? thats the first thought that came to me since it probably hasn't been used much until i got a hold of it. thanks, i will check that site out. also my dad's friend works on tube amps a lot, he fixed it once maybe he will do it again for me.

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<monty python>These kids today... they don't how good they've got it...</monty python>

Changing tubes is really just like changing a light bulb. The hard part nowadays is that the local drugstores and 5-and-dime don't have the tube testers like they used to. If you can find a tube tester, you can plug each tube in and find the bad one. Then you could just replace the one tube. But, since the amp is as old as you say it is, you would be better off just getting a whole new set.

Just make sure you get the right replacement tubes and you'll be ready to rock.

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Jehle, I have to disagree with you on this one.

The amp's bias has to be set with a new pair of power tubes....

We're talking old Fenders here..

Yeah, setting the bias will make it perform at its best. Good point.

Being the cheap person that I am though, I would get a matched set to minimize any DC drift through the speaker. I assume that with the two power tubes that it's in push-pull configureation. I think most Fender amps are designed like that because they are supposed to be clean sounding.

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I would get a matched set to minimize any DC drift through the speaker. I assume that with the two power tubes that it's in push-pull configureation. I think most Fender amps are designed like that because they are supposed to be clean sounding.

these late silverface master volume Fenders are probably different beasts.. not sure though

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I actually don't like fender amps at all, so I really shouldn't even comment. B)

The only tube amp I've ever tinkered with is an old 1950's Grundig. It has one EL84 and one 12AX7. It's a great little blues kit, but about as dumb of an amp as they come. Bias? What's that? I would have to file down resistors to bias the thing. :D

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Best buy I ever made about 5 yrs ago. I found a garage sale that was selling a Jackson-49 tube tester, 5 BUCKS! Sure, its old but then again so are vaccuum tubes.

Anyway, you got some troubleshooting to do. There are several possible causes for the distortion you are hearing. Check all tubes with a transconductance tube tester. Remove each tube in turn and see if distortion goes away by putting a known good one in its place.

If you still have distortion after checking all the tubes then check the filter capacitors for leaks or shorted/open circuits. These are the little buggers that store a charge, even with the amp unplugged. At this stage I would definitely recommend taking the amp in for a check up. Those caps can knock you on your ass if you aren't careful.

Another quick check is to test the output transformer for shorts or opens. Distortion could also be caused by bad plate, cathode and control grid resistors. You have to know what you're looking at so if you haven't a clue when it comes to reading schematics then bring it on in to the doctor.

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