Peavey Classic B Series - Plate Current

[tdlunsfo]

It was a little out. ~43Vpp and 14.9Vrms at the output. I usually run at 500hz. I have a Fluke87V which I think is good till 200kHz.

[Helmholtz]

I have a Fluke87V which I think is good till 200kHz.

Also have a Fluke 87V. Specified bandwidth is 20kHz, which is very good for a handheld DMM.

Anyway the PI signals should not show any signs of distortion at that low level.

[tdlunsfo]

Ok. I'll get some voltage readings on the PI tomorrow. I did glance at the 24v feed to the PI earlier and it was 22v.

[tdlunsfo]

No load PI Voltages:

330V PS feed = 311V
Collector 180V = 175V
Base 25V = 24.8V & 25V
Emitter 24.4V = 24.4V

Same readings with the NFB connected

[tdlunsfo]

More readings at 60mA and 48mA on the tubes (when they really start drifting apart). Approx 5 on the normal volume with MV maxed. Heavy distortion on the output.

With NFB:
350V - 208V
180V Top R - 95V
180V Bottom R - 88V
L Base 25V - 22.2V
R Base 25V - 22.4V
Emitter 24.4V - 22.1V

W/O NFB:
350V - 203V
180V Top R - 90V
180V Bottom R - 87V
L Base 25V - 22V
R Base 25V - 22.3V
Emitter 24.4V - 22.1V

[Helmholtz]

[QUOTE=tdlunsfo;n978877]More readings at 60mA and 48mA on the tubes (when they really start drifting apart). Approx 5 on the normal volume with MV maxed. Heavy distortion on the output.

With NFB:
350V - 208V
180V Top R - 95V
180V Bottom R - 88V
L Base 25V - 22.2V
R Base 25V - 22.4V
Emitter 24.4V - 22.1V

Does that mean the PI supply voltage drops from 311V (no signal) to 208V at large signal?

The PI itself looks good.

[tdlunsfo]

[QUOTE

Does that mean the PI supply voltage drops from 311V (no signal) to 208V at large signal?

Correct.

[Helmholtz]

What happens to main B+ at the OT CT when the output starts to clip?

What is the heater voltage?
What is your actual mains voltage at the PT primary?

[tdlunsfo]

Do you want heaters and mains at idle?

[Helmholtz]

Do you want heaters and mains at idle?

Yes.
Wondering about low supply voltages even without signal.

[tdlunsfo]

What happens to main B+ at the OT CT when the output starts to clip?

What is the heater voltage?
What is your actual mains voltage at the PT primary?

main B+ at the OT CT when the output starts to clip = 433Vdc vs 500Vdc idle
heater voltage = 6.9Vac
actual mains voltage at the PT primary = 123Vac

[Helmholtz]

A B+ of 433V should allow for at least 45W clean output into correct load, provided there's sufficient grid drive and screen voltage.

What is the screen voltage at the onset of output clipping?

[tdlunsfo]

A B+ of 433V should allow for at least 45W clean output into correct load, provided there's sufficient grid drive and screen voltage.

What is the screen voltage at the onset of output clipping?

470Vdc. ~38W at the start of clipping.

[Helmholtz]

470Vdc

Scren voltage can't be higher than main B+ at same operating condition.
Sure you measured at max clean output? Best use the same output that caused the 208V PI supply voltage.
I'm trying to find out why the PI supply drops that low.

[tdlunsfo]

Using the previous settings the screens are 366Vdc