Peavey Delta Blues - Mysterious Zener diode in HT supply

[lalunatech]

Hiya
I have a Peavey Delta Blues in for repair with a few faults. The main one was a snapped power resistor wire in the HT supply dropper chain. (R58 between Plate and Screen voltage points). A zener diode dropping 57 Volts was added in series with R58 (470 Ohm) between J20 and J21 terminals. The Screen Voltage is dropped to 292V and the B++ to 248V instead of 275V. Because the junction of the zener and R58 was hanging in the air, the wire snapped with vibration. The amp is only putting out about 12 Watts into 16 Ohms which I think might be a consequence of the low Voltage supply to the PI. Is this zener a factory mod or do you think someone has added it to limit the output?

Any help greatly appreciated.

[Jazz P Bass]

The zener was added.
The old 'my B+is too high' routine.

Please give Peavey a little credit.
As they are a professional organization, I highly doubt that they would pull a stunt like "components hanging in the air".

peavey_deltablues.zip