1979 Fentder Twin, Output hum.

[isaac]

Just as a thought, did you try replacing the 20uf's with 20's? Or did you go straight to 47? I've found that lots of times I fix something and I assume that I got it fixed, whereas when I replaced that part with the original value, the replacement part was bad, so eventually I found that and it was fixed. My point is that, the amp came with a certain value and it worked, so you have to be careful of using other values/parts as bandaids. Anyway, good to hear it works.

I hope you got the jist of what I'm trying to say. I know that I can see that my explanation here doesn't do "as" well as I'm trying to say, but I think a regularly smart person, (as I'd think everyone on here is, we do work on amps.... ) can see my point. I could do better in person, but this should work...

[catstrat]

Hi Isaac. In the beginning i used 22 mfd 450 volts. When that didn' fix the hum i pulled them and checked them with a cap tester i have. The meter showed they were good. Simply because something is new does not mean it's good. After thinking about it and out of despiration i installed the 47 mfd caps. I've found in situations like this , if the fix works, even if it's not orthodox, run with it. It's the same as looking for a broken wire. Sometimes it's easier to just run a new wire. Since i do this for a living i can't afford to get bogged down on any one amp. As i've said, in the end ,if the customer is happy, i'm happy. Thanks for the input everyone.

[JoeM]

I suspect the 22 mfd was defective even though it may have tested ok using a cap tester. Many Fenders I've had (and have now) use 22 mfd in that circuit location and don't hum.

[isaac]

I agree with Joe, same thing I pointed out a couple posts ago, on this very thread, sometimes testers don't get everything. If it were I, (probably since I'm OCD pretty bad...) I would definitely try 22uf's again... But everyone's happy here, so I guess that is a good reason to resist the temptation...

[catstrat]

Hello everyone. It probably was a defective 22 mfd cap. I have a huge problem myself trusting any piece of test equipment. I don't even trust a calculater. LOL. But on the other hand as far as filter values go, i hear some people increase the filter values as part of a mod. It's supposed to increase the bass response or something like that. Someone on here knows more about that than i do. I figure the 47 mfd caps will give a little more filtering and it may change the tone somewhat, but it's working now and that's what the customer wanted. Thanks everyone.

[JoeM]

Yes, I think going up to 47 mfd from 22 gives a bit tighter bass, at least in a few Fenders, (i.e. for the plate and screens, downstream I use 20 or so). But it's not a real drastic change IME.