Pendulum Audio Quartet. Plate voltage too high? 6922

[mkiijam]

I'm getting about 250V on the plates of these tubes (there are 3 in a Quartet). One had a burnt up plate resistor, but the tube seemed fine, although it was worked on by another person before I got it.

 

[pucho812]

Data sheets for the tube say Max plate of 220VDC
Is that with the resistor replaced?

 

[rock soderstrom]

The maximum permissible voltage that you measure at the plate also depends on the topology. A 6922 in a SRPP circuit may well have 240V at the upper plate. This also applies to other circuits in which a triode system stands on another triode system.

With a grounded cathode circuit, the maximum plate voltage would be exceeded, thats true.

Is there a schematic?

 

[mkiijam]

Data sheets for the tube say Max plate of 220VDC
Is that with the resistor replaced?

Yes, I replaced it.

Is there a schematic?

That would be too easy. No. Nothing that I can find so far.

 

[rock soderstrom]

That would be too easy. No. Nothing that I can find so far.

Ok, I see. You can measure against the respective cathode (not ground) of the triode system to see how many volts are roughly present at the plate.

 

[pucho812]

Is the unit working? Or is it just the issue of you are unsure what the proper voltage should be at the plate?

 

[mkiijam]

It was / is working, well after I replaced the resistor. I was just trying to be a good tech and figure out why the resistor burnt.

 

[AusTex64]

I have seen 6922’s at 275VDC on the plate in WCF designs and they held up surprisingly well.

 

[rock soderstrom]

I have seen 6922’s at 275VDC on the plate in WCF designs and they held up surprisingly well.

Yes, that is quite possible, as the triodes in WCF only see half B+ voltage each. The maximum Ufk voltage (6922 --> only 120V) is more of a problem here, but this can be compensated with a elevated heater voltage.