distorted output on Selmer T&B mkII (reverb)

[HTH]

Hi all,

I've got a Selmer T&B mkII (reverb) on the bench here with low output; slightly distorted too (among other things like the output bases falling apart). Anyway, I've made it safe and it works, but there is a background distortion to the sound when you play it.

I've ended up wiring the bass channel directly to the PI as if it were a single channel amp to isolate the problem (it was on both channels originally), so it's got to be something in the PI or power supply, right? - I've ended up replacing the caps in the PI, but still the same. Only the bias cap is original, but that wouldn't affect the audio path (right?).

I've narrowed down everything in the preamp as I've rebuilt it to original specs (had previously been modded). I've paralleled some fresh caps in with the originals one at a time to see if that made any difference - made none. The only thing I can think of left is the OT.

(edit): I've also replaced the valves too, no difference.

Anyone got ideas? - all help and suggestions appreciated.

[HTH]

voltages are useful, but look fine (heaters are a healthy 6.5vac)...

V1
1. 111v
2. 0v
3. 1v
6. 112v
7. 0v
8. 1v

PI
1. 295v
2. 28v
3. 44v
6. 287v
7. 27v
8. 44v

EL34s
3. 478v
4. 476v
5. -50v (biased at 33mA per valve)

The only thing that seems a bit 'off' is the bias at -50v with the EL34s at 33mA, but could this be the problem causing the distortion behind the clean tone? (like a mis-biased transistor kinda tone)

[nosaj]

Check your bias resistors, I made the mistake last week of putting in 220 ohm in place of 220k. made a 30 watt sound like a half watt. Do you have a schematic for us?

jason

[HTH]

Thanks for the reply - I've made that same mistake before, 22k bias splitters

I've got it sorted now, was some weirdness in the bias supply - I knew that -50v on the grids with them biased at 33mA looked weird.

The amp is sounding great again and biased at around 36mA with -38v on the grids (about what you'd expect).