Home brew power supply for guitar amp

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Home brew power supply for guitar amp

Post by westcoastjohn on Thu Mar 08, 2012 12:50 pm

I picked up a 1960 cheapo guitar amp for $40 at a pawn shop. It was too light! :>)
The brand name is "Marlin", made in Canada, and it had three tubes, a 50C5 power tube, a 35W4 rectifier and a 12AX7 for two stages of preamp gain. There was no power transformer, so when Sonny plugged his Sears guitar into the thing, he was literally plugging in to the wall socket. I'm amazed how many of us survived the 60's.

I scrounged up two similar salvaged transformers, one from an old tuner and the other out of a big cassette player. When I hooked two of the secondary windings to each other, I got a step up to about 135 volts of isolated AC! That was perfect for the B+. I pulled the rectifier tube and replaced it with a couple of silicon diodes. The trannys had other windings. I found a 6 volt winding to power the 12AX7 heater by using the center tap, and, on the other transformer, a 48 volt winding to supply the heater on the power tube. Now I had a 2 tube guitar amp that was safe to play and louder because of the stepped up voltage.

What about the empty socket ? I added a third preamp stage, I think it was a 6AT6, on a switch. That was overdrive! Cool



westcoastjohn
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Registration date : 2012-01-10

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