Stromberg - Carlson PA Amp MOD for guitar

[Normybaby]

I got this old PA amp from my boating neighbor. His father used it to mic-up his saxophone in a polka band back in the 50’s-60. When I opened up the OT, the date Nov 11 1946 was stamped on the inside cover. It’s a 30 watt, Class AB, Cathode Bias w/ 2) 6SC7, 1 6J5 preamp and a pair of 6L6 Power tubes (I was able to get a schematic for this thing on ebay). He dug it out of his attic were it’s been for the last 20 years. It had about 1/8” thick of packed fine dust inside, on top of the chassis. The output transformer was cooked; all of the caps were dried out. Somebody installed a sorting wire on the preamp 6SC7 cathode to ground. I managed to save pretty much everything else. I made a few mods: raised the voltage on the preamp tubes to 95V from 65V (increased the voltage divider from 47K to 100K) and increased the gain a little(removed the shorting wire from cath resister; was 1.5K changed to 820ohms w/50mf cap) and changed the plate load res from 330K to 270K as well. It had two identical channels (Mic 1 and Mic 2) so I made one channel a bright channel (I forgot to make a sound sample of it) by installing a 500 pf coupling capacitor (sounds too British; I’m going to tweak it a little more with a .022mf). Let me tell you, I love the sound of this thing. I hooked it to a cab with Weber vintage 12 in and stuck a SM57 in front of it and here is a very quick sample and some photos
OK, I'll have to figure out how to attach an MP3 file for the sound sample

[drewl]

Nice...I coulda' had a newer version that was just lying around the warehouse of a place I worked back in the 80's.
But I was into the new fangled tranzeester amps!

[Normybaby]

Thanks, yeh, you and most of us that were around back then went the way of the transistor amp. It's funny how things go in cycles. Some day there will be a vintage transister amp forum and they will be talking about the GREAT TONE of the early transistors.
Normy