GT120 - troublehsooting

[JustinHarvey]

Now interestingly, when I switch off power to the amp, the capacitors are discharging themselves, my A+ reading drops over time which I assume means there is a short somewhere.

The resistors that parallel, and balance, the stacked reservoir caps should discharge the amp when it's off.

[plokij88]

I believe the lightbulb limiter is now behaving the way I want it to.

When i power up (with lightbulb limited in circuit) I have no sound at all. Not even hum or hiss. I have tested the guitar, cables, and speaker and they all work. I have gone through swapping out each power tube one by one but it didn't make a difference.

I have taken readings of everything I can think is relevant, see attached. These were taken with the lightbulb limited IN the circuit, and each el34 was reading between 1 and 2 milliamps on the bias probe. When i took the readings on pin 3 of el34 1 and 2 i could hear a very fait whistling noise.

[plokij88]

Now interestingly, when I switch off power to the amp, the capacitors are discharging themselves, my A+ reading drops over time which I assume means there is a short somewhere.

The resistors that parallel, and balance, the stacked reservoir caps should discharge the amp when it's off.

Ha that occurred to me when I woke up and i rushed to edit it out of my post but you beat me to it!

[plokij88]

Can anyone explain to me what's going on here. This is the secondary side of the Output transformer. Blue is ground the other colours are 4/8/16ohms. All of the top row have continuity with each other, all of the bottom row have continuity to each other. None of the top row have continuity with any of the bottom row.

Thusfar I had only used one wire of each colour, assuming that they were wired to the same point. And of course I had used ground, 4ohn and 8ohm from the top row, and 16ohm from the bottom row.

[nuke]

You might be able to contact PRL and see if they can confirm how the component was wound.

I think these might be the exposed interleave windings on the secondary side.

Was this transformer originally in some sort of packeting or with attached terminal strips? It seems 'bare' to me, like it is missing the end bells or the mounts or attached solder terminals.

I'd guess that each color is supposed to be connected with the other wire of the same color, blue-to-blue, orange-to-orange, etc.

But that's just a guess.

[nuke]

Also - ping RG on this question. He's got a lot of experience with transformers.