Hi, I'm new to the board here and found it while searching info about the amp.
I just got it a few days ago and first learned that it needs a footswitch to work right.
Am I correct though that jumper-ing the top two slots on the head's footswitch plug engages the red channel while jumpering the bottom two engages green (might have that reversed, but you get the idea)?
So that's what I did to test the thing out. Then I got this oscillation happening as you can see in these videos I made for the Ebay seller.
https://youtu.be/kj2teugcLP8
https://youtu.be/p-Ev1hTTzKs
I misspoke in the "red channel" video because the green channel did howl as well.
Today I opened it up, looked for anything obvious, couldn't find anything, cleaned the pots, and tested the spot on the board at the junction of the 1K and 1.5K resistor and it measured about -16.8 volts. I figured that was ok since the schem said +/- 10%. I probably should have tested other points but I just figured I was good to go. The schem though, the trim doesn't seem to sit in the same spot on my board as it does on the schem.Maybe I'm way off, but it seemed the trim on my board was located where the thermistor is drawn in the schematic.
here's the schem I'm referencing
http://el34world.com/charts/Schematics/files/randall/Randall%20RG100.PNG
So I plug it into an 8 ohm cab, leave the reverb disconnected, fire it up and it sounded good, aside from some background noise when not playing which i just assume is the hissy nature of fets. There was no more howling. I continue to jam along for maybe two or three minutes and then all of a sudden I lose a ton of volume. I powered it down and checked for continuity between pins on the power transistors and found that I did have a direct path from base to emitter on the outer pair of transistors (had done this previously and had no continuity between connections).
So, other than dead 2n6254's, anything else you can think i should look at? I had the amp opened up while playing and there was no smoke and no funny smells. I didn't see any resistors go poof.
I'm not a total newb, but there's a ton I don't know. I've done a lot of work with tube amps and only some work/trouble shooting on SS gear. SS power amps are not anywhere near intuitive to me yet.
Thanks
I just got it a few days ago and first learned that it needs a footswitch to work right.
Am I correct though that jumper-ing the top two slots on the head's footswitch plug engages the red channel while jumpering the bottom two engages green (might have that reversed, but you get the idea)?
So that's what I did to test the thing out. Then I got this oscillation happening as you can see in these videos I made for the Ebay seller.
https://youtu.be/kj2teugcLP8
https://youtu.be/p-Ev1hTTzKs
I misspoke in the "red channel" video because the green channel did howl as well.
Today I opened it up, looked for anything obvious, couldn't find anything, cleaned the pots, and tested the spot on the board at the junction of the 1K and 1.5K resistor and it measured about -16.8 volts. I figured that was ok since the schem said +/- 10%. I probably should have tested other points but I just figured I was good to go. The schem though, the trim doesn't seem to sit in the same spot on my board as it does on the schem.Maybe I'm way off, but it seemed the trim on my board was located where the thermistor is drawn in the schematic.
here's the schem I'm referencing
http://el34world.com/charts/Schematics/files/randall/Randall%20RG100.PNG
So I plug it into an 8 ohm cab, leave the reverb disconnected, fire it up and it sounded good, aside from some background noise when not playing which i just assume is the hissy nature of fets. There was no more howling. I continue to jam along for maybe two or three minutes and then all of a sudden I lose a ton of volume. I powered it down and checked for continuity between pins on the power transistors and found that I did have a direct path from base to emitter on the outer pair of transistors (had done this previously and had no continuity between connections).
So, other than dead 2n6254's, anything else you can think i should look at? I had the amp opened up while playing and there was no smoke and no funny smells. I didn't see any resistors go poof.
I'm not a total newb, but there's a ton I don't know. I've done a lot of work with tube amps and only some work/trouble shooting on SS gear. SS power amps are not anywhere near intuitive to me yet.
Thanks