repairing Golden Age pre 73

[jtn191]

Hey all,
I got a pair of Golden Age pre 73s on discount from Musicians Friend. Both were missing power supplies but only one seems to be slightly faulty. Here's the deal: when powered on, the signal LED lights up and there is a constant, low hum. I poked around with my DMM and I got a reading of ~35v on the 24v pads. I turned the trimpots and something started smoking...it seemed to be coming from the 2N3055...

Mine is similar to the one pictured below, but the power supply pcb is a different revision
Thanks for any help

 

[3nity]

Start by looking if theres a L7824 regulator on the connectors board.
then measure all 3 legs one of them should show 24Vs.

 

[jtn191]

on the "TIP122" regulator I got 51, 67, 52v

and on the regulator with heatsink: 33, 34, 35

 

[gemini86]

Disconnect the power supply from the preamp before you smoke everything. Sounds like that 7824 has no ground connection. Check the traces on the bottom, make sure the regulator ground pin is grounded. Maybe use an alligator clip to see if you can get it working.