Bias voltage problem with plexi 50w build

[Silvio55]

Hi! I just finished my 1987 plexi 50w build, I checked all voltages and all seems to be right, except the bias voltage at pin 5 of power tubes, it´s high, -7.8v, when it shoud read around -40v, I checked the bias circuit and all is ok. Here´s the schem of the bias circuit:

I have installed a Lar/Mar type PPIMV, but again I checked everything and all looks correct. The thing I noticed is that I have 325v entering at the bias circuit, wich is fine, then 220v after the first resistor (220k), but then only -12v after de diode, is it normal?

[Jazz P Bass]

Check the PPIMV for miswiring.

-10Vdc on the bias pin will red plate for sure.

[Silvio55]

Thanks Jazz! I will check that again, but is it normal to have a reading of -12V right after de diode? I think it shound be a more negative voltage there, or it could be related to a miswiring problem at the PPIMV?

[J M Fahey]

There's a problem there.
With no load (connected only to EL34 grids which are an open circuit) the pot adjustment range will go from around -32/34V to some -46/48V
It's normal to read much less at pin 5 (that's why it's forbidden to read there, it's useless and can only cause trouble) but you should have proper bisa voltage at the last cap.
Unless you wired it upside down, that is
As in cathode (can) to ground

[Silvio55]

Juan, you´re absolutely right, my caps were upside down, (I fell like an idiot), just reversed them and voila! a perfectly working amp!
Thank you!

[Jazz P Bass]

I would recommend replacing those caps.

They do not like being reversed, one bit.

[Silvio55]

I would recommend replacing those caps.

They do not like being reversed, one bit.

Thanks Jazz, I will replace them as soon as I get new ones.