12.000 no sound

[Sral68]

Hi!

I have an issue with my self built 12.000.
It has worked fine since I built it. Recently I wanted to try some different tubes. They fired up and biased ok, but once I put the amp back in the box it stopped working. I took the amp out, checked the voltages and they were fine. I reinstalled the old tubes and got sound. But now its stopped working again.

Obviously something has given up or I have a bad connection somewere, but I need some help for where to look.

Some details.
The fuses are fine (checked with multimeter) and the amp light comes on.
With the standby on I can hear some noise when I touch some of the connections with the mulitmeter.
I went over the checklist for the 100 watt kit, and voltages seem to correspond roughly.
There is only filament light on V7. I tried switching the tubes around, but the tubes light up in V7

I'm at a loss here and any help would be appreciated

[alanp]

If only V7 lights up, have you checked that heater (filament) voltage is getting to V1 to V6?

[Sral68]

Hi!

I have voltage on the heater wires 2.9 ac

I also have voltage on the resistors of pin 5 on the power tubes. It changes when I turn the bias pot.

[Sral68]

I resoldered the heater wires on V1. No I have filament light in all the power tubes. The light in the preamp tubes is difficult to see, but they get warm.

I can bias the tubes, both in HiW and LoW, but still no sound.

When I probe around with the multimeter I can hear some scarping sounds. I also get a scarping sound when I turn the presence control. The other controls are dead.

[Sral68]

Got the sound back after going over my the preamp, and touching up here and there.

I tried Friedmans fat cap mod in V2a, but had to resort to the old setup. I think the legs of the 68 uf i tried were to short. I tried to extend it with bus wire. Not sure if this was the problem.

Puh. I have to use this amp in the studio on thursday