I want to share an interesting information for you

[Celena]

Greetings experts and enthusiasts,

I’ve recently found my self in the possession of a Stromberg-Carlson Signet/22 PA amp. It came out of the local train depot and was absolutely buried in coal dust so I blew it out with compressed air and inspected it for any obvious problems and none were found. After a thorough cleaning I connected it to a speaker and ran it through the light bulb tester and it slowly came to life. I went from a 40 watt bulb to finally a 100 watt bulb and confident that nothing was majorly wrong I ran it direct. It seems to be working and was sensitive to a tap on the old style mic connector and after several minutes I noticed one of the EL84 output tubes was beginning to red-plate so I shut it off and discovered on the tube tester that the tube was shorted. I replaced the electrolytic filter caps and ended up replacing both OP tubes with matched JJ’s and replaced the 150 ohm 3 watt bias resistor that measured 127 ohms. I ended having had to add a resistor to balance the tubes, changed out the Mic 1 connector with a 1/4” jack and let it burn in for a few hours. The tone decent with both single coil and humbucker pickups but now I’m ready to begin its metamorphosis into a guitar amp.

I’ve repaired/restored rescued several vintage fender amps as well as early Philco consoles and AA5 table top radios over the years, and replacing bad parts (once they are located) is one thing but changing the tonal characteristics is something I've never done. There are several of these amps out there that have been modified into guitar amps but I have been unable to find out just what the tech did.

Your suggestions would be greatly appreciated!

[pompeiisneaks]

You've come to the right place. Someone already had a thread on this:

https://ampgarage.com/forum/viewtopic.php?t=31091

I'd think as I mentioned there, just adding a cathode resistor and capactitor typical in fender or others would give it more of the tone you may be looking for? One change at a time would be a good start, maybe adjusting coupling caps etc.

~Phil