Fender Twin Amp

[drewl]

That's right folks, the black knob "evil" twin, between the Red Knob and Pro (Zinky?) designed....looks like I worked on this back in '95!

Aside form an intermittent output tube socket, this one the Red channel feeds back/howls and the tone controls don't seem to work.
Also the volume controls don't kill the signal all the way.

Checked simple things like the pots and grounds of the tone stack, but the problem seems to be signal bleeding from somewhere else.

after scanning through 24 pages of search results, I found that one of you kind people posted the Service Manual back in 2016, Thanks!

It seems there was an issue with channel/signal bleed and the manual has a supposed remedy. I'll have to see if that cures it, hopefully.

The manual has a few ECN's.

Anyway, here's the manual. 94-twin.pdf

[drewl]

Ok, this is weird.

If I remove the first channel switching relay, K1, I still get signal bleed showing up at V2b, if I ground the signal going to the relay coming off the first preamp stage, no signal bleed.

Somehow signal is leaking from that first stage into the amp.

I'm guessing a bad ground or possibly bad jack.

[drewl]

And I have signal to the power amp when I plug a cord into the fx return jack!

[drewl]

AH HA!
SIgnal on the filter node C43, jumpered a cap across it and the amp works correctly

[The Dude]

Glad we could help!

[drewl]

Oh, you've helped a lot over the years!

Sometimes just talking or typing it out can help lead to the solution.

[The Dude]

I was of course joking, but I totally get it. Sometimes, putting down the tools and just letting your brain work helps a bunch. I couldn't even count the number of times I get stumped on something at work and then the solution pops into my head just sitting around at home away from the problem.

[Chuck H]

I was of course joking, but I totally get it. Sometimes, putting down the tools and just letting your brain work helps a bunch. I couldn't even count the number of times I get stumped on something at work and then the solution pops into my head just sitting around at home away from the problem.

Which is precisely because your brain never let go of the problem. It just runs on the back burner on simmer. When I'm at the bench in the middle of a good corker the wife sometimes tells me I should take a break. She's seen the process enough times. What she doesn't know is that although that seems to work it's not the stress relief that gets me to the other side. It's just retuning my brain in a different direction that allows me to reconfigure how the problem is evaluated. To her it looks like I'm not having any fun and she just wants me to separate myself from the stress. Which is actually the opposite of what happens. She also doesn't think it looks like fun. Which it doesn't (maybe it's the curse words?). but it is fun. My kind anyway

[drewl]

I was of course joking, but I totally get it. Sometimes, putting down the tools and just letting your brain work helps a bunch. I couldn't even count the number of times I get stumped on something at work and then the solution pops into my head just sitting around at home away from the problem.

I'll never forget, back in the 80's I was working on an oscilloscope that had a horizontal amp problem.

The solution came in a dream. My mind saw the problem when I didn't.

[Enzo]

No joke at all, I often tell people who have been staring into an amp for hours getting nowhere, just turn the amp 180 degrees. Working with the knobs pointing away instead of towards. It really does give a new perspective. Look at something long enough, and even if it is wrong, it comes to look right.

I know when I learn some new lick on the guitar, and I practice it, if I set the guitar down for a few days, when I return, it all seems to fall into place. I used to shoot pool every night in the bars. I'd work on some nuance of the stick and ball control, and if I stayed away a few days, when I returned, the motion had come together. know those are physical, but it was working in my mind all along.

[Chuck H]

I know when I learn some new lick on the guitar, and I practice it, if I set the guitar down for a few days, when I return, it all seems to fall into place.

Wow! Ditto.

I used to shoot pool every night in the bars. I'd work on some nuance of the stick and ball control, and if I stayed away a few days, when I returned, the motion had come together. know those are physical, but it was working in my mind all along.

It's all part of the same thing. Anthropologists think it's part of the "Great Leap Forward" (50,000 years ago-ish) regarding the modern human mind. Once upon a time, and not long ago, we couldn't personally evaluate rote, learned activities with criticism. Things were known or not known. Then somehow our different minds came together in links. Our critical mind was now able to see physical, quantitive, spiritual, previously derived and speculated outcomes for activities. I'm not sure I think it was actually that humans had none of this and then all of this (in fact I'm not sure it even relates to all people today). But I know that a linking of the different minds, equated to critical thinking, is responsible for anything we have created culturally and technologically. Without this link we'd still be chipping stone and stabbing bison. (not exactly, but yeah)

[Enzo]

Do you know the difference between a buffalo and a bison?

[Enzo]

You cain't wash yer face in a buffalo...

[xtian]

Do you know the difference between a buffalo and a bison?

No. But,

[g1]

Do you know the difference between a buffalo and a bison?

Bison don't have wings.