Metropoulos Forum

New on the forum and could use some help. I have a Marshall 1973 Lead 50W and the Drake 120-164 Power Transformer that smoked itself recently. I am looking for the original schematics to try to figure out a suitable replacement and open to any ideas on a suitable model that I could put in it. The I/O and Choke are all stock for 1973.

Thanks

Welcome to the forum! Things have gotten slow around here lately so you may not get a lot of responses but I can help to point you in the right direction. Many of these 50 watters had a factory wiring error in the bias supply that caused the PT to burn up in a bunch of these amps. The bias wire was accidentally attached on the wrong side of the standby switch causing the tubes to be without bias voltage for a few seconds when you throw the standby switch into play mode. If your amp has this wiring mistake, you can move the bias feed wire to the other side of the standby switch or just leave the standby switch in play mode at all times and use the power switch to turn the amp on and off.

Any 50 watt PT will work fine. You just need to know if your PT is the lay down style or the upright type. Here are a few options to choose from.

https://shop.amppartsdirect.com/collect ... ansformers
https://shop.amppartsdirect.com/collect ... apd-8089-h
https://www.tubesandmore.com/products/t ... t-marshall
https://www.mojotone.com/British-Style- ... ransformer

The first two at Amp Parts Direct are out of stock but they restock often so keep checking back. Any of these models will work fine as long as you get the correct mounting type.

Just to be sure the PT is actually bad, have you disconnected all of the secondary wires and tested the PT by itself? There are several other parts that could be faulty and preventing the amp from powering up.