Pop/click in tube amp

[Stevem]

You do not have to yank out preamp tubes to test the circuit around them, just use a clip lead to place a short across each plate load resistor. This makes the circuit act like there's no plate load resistor and with no plate load resistor there can be no gain / no sound.

I just last night fixed a Fender Rivera era Twin reverb II that was popping and clicking within 3 minutes of turning it on even out of the cabinet. The cause turned out to be two 2 watt carbon type 390 ohm resistors in the bias circuit that where burning up to point that one of then was starting to show signs of cracking and both with burning the tag board up where the solder rings are.

On your amp a quick thing to do is to just replace the 2 plate load resistor on each preamp tube just to rule those out as they can cause the clicking issue you have.

If they are not 1 watt metal film type resistors I would upgrade them to such as they will be overkill and make for less gain hiss at high volume settings.

[goldenGeek]

Thank you @stevem, I will try that tomorrow. Here's the schematic I drew up in a hurry, I added values where it was easy to read on the components. I'm not sure if this is absolutely correct, but I think it's close.

[Stevem]

R3, r11and r20 and 21 are the plate load resistors that can make for popping issues, although one you turn on the amp and they start to make noise they don't stop.

The plate load coupling caps like the 330pf the .022 and the two .1uf are candidates for popping issues for sure.

[goldenGeek]

Hello Now I have replaced almost all components and I'm leaning more and more to the bad transformer theory that was mentioned early in this thread. Just one thought - could the board be bad and cause a buildup that will burst once it reaches a high enough current? I have tried to measure but I'm a bit unsure what is the best way to do that. Anyway, I think i have the final schematics reverse engineered at last I have measured some components and some is based upon color/writing on the component.

[xtian]

could the board be bad and cause a buildup that will burst once it reaches a high enough current?

Yes, this is possible. Fender's vintage fibre boards are known to absorb moisture and become conductive. What's your board material?

Another common thing is for PCB to become conductive after being scorched by too much heat.

[goldenGeek]

Im not sure what material it is, here is a picture:

0CBE28D0-270B-4022-B479-4919866378AE.jpeg

[xtian]

Dunno. Looks like fiberglass. Try measuring resistance between to adjacent, unconnected terminals.

[Stevem]

Try this, find the red wire that feeds the primary side of the Output transformer and unsolder from its supply sorce, do you then still read a pop on your scope?

[goldenGeek]

I did not see that last answer right away so I haven't tried that yet. However, I found a Weber output transformer (W404248, "only" 40W though, but for testing I think thats okay) that I forgot that I had. It has similar specs as the original so I tried it and it seems like the popping is long gone... I will have to wait a little while longer, but it seems like it is a bad transformer I'll let you know how it goes.

[Mac Dillard]

might want to give this a try https://www.premierguitar.com/articles/ ... r-tester-1

[Stevem]

That tester does work as I have made one, but it only works when there's a constant short when there's no power applied.

With his issue it's a intermittent short Only when it arcs, so I do not believe that tester if he where to build it would show anything wrong.