Amp BIAS issue? HELP PLEASE!

[PeterJ_22]

Hi guys so after a week of playing my newest build I thought I'd check voltages etc.

Heaters are 3.3 volts per side so 6.6-6.7, a bit high but should be ok.

Preamp voltages on the cathodes are about 10% lower than George's kit chart, and the plates are around 1 (meant to be 2?)

The Issue is when I bias the amp.

V4 reads 0.040 volts DC
V5 reads 0.040
V6 reads 29 volts ???????????????????????????????????????
V7 reads 0.036

Also I had to turn the ppimv right down to stop a crazy hum noise etc coming through the speakers as I biased it.

Finally thats as low as I can bias it, should they all be around 37ish? If so what do I need to change on the bias circuit to give me that range?

Any help would be much appreciated, no idea why v6 bias is so all over the place??

[PeterJ_22]

So I swapped v6 and v7 tubes around to see if it was a tube, apparently the tubes are fine, assuming its something to do with that socket wiring / components?

[PeterJ_22]

Ok so I think I fixed my own problem. The 1ohm resistor going to ground was stuffed. I replaced it and all seems normal.

Bias voltages range from 0.035 - 0.039

So I'm assuming thats where I want it

[PeterJ_22]

So new problem the amp is making a weird humming noise and when i play a guitar through it its making a strange motor boating sound and sounds like it has some sort of weird envelope filter on it or something?

One thing to note is on V4 I accidently touched something with the multimeter probe whilst biasing and it had a bang and sparks etc, Could I have blown something on the board?

[neikeel]

I would suspect a poorly tube.....

[PeterJ_22]

Power or preamp?

[neikeel]

Power or preamp?

Typically power amp if you had sparks whilst biasing.
Preamp tubes (V1 or V2) usually whistle or crackle a duff PI tube can give imbalance with hum and motorboating but so can a failed mains or screens filter can.

[PeterJ_22]

Thanks for the response.

Is there any way to test what might be wrong before I go and order new parts?

[PeterJ_22]

Ok so luckily for me I just tried another phase inverter tube and all is well!!!!

Glad I did that as I was about to order another set of EL34s!

Thanks again for the help