Marshall 1987 Plexi PSU design help/criticism

[ValveBytes]

Hi, I recently took apart an old amp and decided rightly or wrongly to turn this thing in to a marshall amp, the old amp was running 4xECC83 and 2xEL34 I later realized, the PT was a bridge rectifier type and had quite a different layout from what the marshall schematic is using, anyway I have come up with a circuit for the power supply based off of this transformer. Oh 1 other question is it normal that the HV secondaries read 193v on one and 130v on the other?



The 380v is the estimate that I got from PSU designer with a similar setup, the 500v is a reading I have taken from that PT with a bridge rectifier and one cap connected, without anything connected to the bridge it reads 363v and the range on the bias winding is -19v to -55v also the bias winding pot is 25k not 10k as in the schematic.

is putting a standby switch on the output of the bridge an ok idea?

any help or criticism would be great on this!

cheers,
Jim

[loudthud]

You will not get a valid AC reading on the HV secondary by measuring each side to ground. You must measure between the two wires (use extreme caution). Also, a DC reading could be inaccurate if the standby switch isn't closed.

The 1.2K resistor is way too high a value. It will probably start a fire unless it's a 50W resistor. Something like 10 to 50 ohms at 10Watt is as high as you should go there.

The bias pot is not in a safe position in the circuit because if the pot fails, you will have no or reduced bias. It's better to put it in the ground leg so if it fails, you have more bias.