66 Pro Reverb blowing fuses after I replaced some components

[Enzo]

Ah, I don't know that we ever established you had a AA165.

A dirty pot would not make the voltage on the cap go away.

[sthomas]

99% sure I figured it out!

Ah, I don't know that we ever established you had a AA165.

A dirty pot would not make the voltage on the cap go away.

Hi Enzo,
I was testing @ the bias cap white/wire junction and a spark appeared beneath the small cicuit board. Seems solder had burnt through the little black paper on the back of the little circuit board and would make intermeittent contact with the chassis. I put electrical tape on the back of the circuit board and raised the cicuit board about 1/8". Hooked it up and it is -69.9 to -70.0. The reading goes back and forth between the two every 1/2 second or so. Thoughts?

[Enzo]

There you go. Problem solved.

Look over the back of that little board. If there are any sharp wire ends sticking out, trim them off. If there is now a little hole under one of the solder joints, is it possible to turn the insulator over so the hole is elsewhere?

Got a dead credit card or something similar of plastic? Cut a piece of that and place under these boards to act as an insulator.


I sure would not worry about the voltage there moving a tenth of a volt. set your meter to AC volts and plug into a wall socket. Watch the "120v" there changing moment to moment. If that changes, then every voltage inside the amp will change as well.

[sthomas]

There you go. Problem solved.

Look over the back of that little board. If there are any sharp wire ends sticking out, trim them off. If there is now a little hole under one of the solder joints, is it possible to turn the insulator over so the hole is elsewhere?

Got a dead credit card or something similar of plastic? Cut a piece of that and place under these boards to act as an insulator.


I sure would not worry about the voltage there moving a tenth of a volt. set your meter to AC volts and plug into a wall socket. Watch the "120v" there changing moment to moment. If that changes, then every voltage inside the amp will change as well.

Thanks again Enzo. Got the problem fixed. I fired it up and tested for about 15 minutes and sounds real nice but I think I need to try another pre-amp tube or tension the socket. Seems to be a bit of noise there from certain note vibrations. How in the world do you tension one of those tiny pre-amps sockets?

The amp is pretty quiet except when the volume is @ 0 to about when sound comes out. Any ideas there?

[Enzo]

Quiet except when it is barely cracked open? Tell me this, do you actually use the amp set like that, or is it just that you can detect some noise if you carfully set the knobs looking for noise? Noise comes from many sources, and each source has its own cure. SOmetimes people complpain that their volume control cqan be at zero and still a little sound leaks through. Then I have to wonder, do they expect to be playing with the amp all the way off much? Is this a problem for you? If not, then don;'t sweat it.

To tighten any soclet pin, we generally push a pointed object between the pin and the wall of the hole, thus compressing the circumference of the pin. In the case of the smaller sockets... use a smaller pointed object. I find a large safety pin straightened out works great. A very fine point to get into tight spots, yet a pretty strong metal that doesn;t bend all that easily. Other potential tools - jeweler's screwdriver, dental explorer.

[sthomas]

Volume

Quiet except when it is barely cracked open? Tell me this, do you actually use the amp set like that, or is it just that you can detect some noise if you carfully set the knobs looking for noise? Noise comes from many sources, and each source has its own cure. SOmetimes people complpain that their volume control cqan be at zero and still a little sound leaks through. Then I have to wonder, do they expect to be playing with the amp all the way off much? Is this a problem for you? If not, then don;'t sweat it.

To tighten any soclet pin, we generally push a pointed object between the pin and the wall of the hole, thus compressing the circumference of the pin. In the case of the smaller sockets... use a smaller pointed object. I find a large safety pin straightened out works great. A very fine point to get into tight spots, yet a pretty strong metal that doesn;t bend all that easily. Other potential tools - jeweler's screwdriver, dental explorer.

Hi Enzo,
I can live with the louder buzz but was just wondering if it's something that needs to be addressed. I will explain further. With the guitar volume off and the amp @ zero, there is a hum/buzz. Still with guitar volume off, as I turn the amp knob up, the hum/buzz continues and uniformly increases with the volume knob increase. Then at about 2 1/2 the hum/buzz goes away incrementaly (though quickly). As I continue to turn the knob @ about 4, the hum/buzz starts to come back again and increases uniformly again all the way up to ten. Could it be grounding?

The amp sounds fantastic!!!!!!

I will tighten the tubes today.

Thanks for all your help Enzo

[Enzo]

Oh, well I hope you don;t mind the hum. It took a lot of back and forthing to fix that bias short. Fixing this will take months. What you have is two different sources of hum that happen to be out of phase with each other at the point of that volume control. That minimum point on the control is where they exactly cancel. To solve it, you need to find the source of BOTH hums, and then take steps to cure each. It is not A hum problem, it is at least TWO hum problems.

[sthomas]

The hum is not a big deal

Oh, well I hope you don;t mind the hum. It took a lot of back and forthing to fix that bias short. Fixing this will take months. What you have is two different sources of hum that happen to be out of phase with each other at the point of that volume control. That minimum point on the control is where they exactly cancel. To solve it, you need to find the source of BOTH hums, and then take steps to cure each. It is not A hum problem, it is at least TWO hum problems.

Thanks again Enzo. You have helped immensley. The hum/hums is not a big deal to me, just thought if it was a quick fix I'd do it. The amp sounds fantastic. Interesting note: It had a big 5U4 rectifier tube in it from the previous owner and I put in the correct tube in around when all this started. I'd remembered a more pleasant tone before the amp started shorting. This morning I put the 5U4 back in and I prefer the sound, seems warmer than the correct tube.