Howdy, y'all. I brought home a Randall RG80ES head to add to the growing vintage-SS collection. Unfortunately, the big selling point of these amps - the distortion channel - is not fully functioning, and I'd like to get it going.
I am at a very basic level of electronics knowledge - happy to dig into things, avoid getting shocked by filter caps, totally willing resolder a component here and there, but I'm def not great at actual theory or troubleshooting. I do note the red channel on the 80/100ES, as shown on the schem, is a surprisingly simple circuit, which gives me some hope I can fix this without dragging it 90 miles one-way to my tech.
Clean side of my 80ES sounds great. The dirty-channel symptoms: extremely low volume (red ch gain / master on 10/10 = volume of green channel on respective 5/1.5), sounds a bit fizzy and the gain definitely sounds way too low vs. the many Youtube clips I've heard.
The amp has two other symptoms: 1) a slight power-supply hum at idle with both channels' MVs all the way down (which may be normal for this amp, I don't know); 2) the famous pull-treble diode clipping is not working at all. I realize the latter could be a bad switch in the pot but the pots are in pretty good, non-scratchy shape as is, so right now I'm guessing it's a circuit problem corresponding to the existing issues on the red channel.
Sound clip of the clean and dirty channels here for direct comparison (I'm riding the fader to add another 10dB whenever I talk, but the amp output itself is always maintained at the same in-room volume throughout the clip).
Getting ready to tear things apart - based on aural symptoms, failing obvious stuff like broken / cold joints and visibly leaky caps, what should be my next thing to examine?
Thanks y'all.
I am at a very basic level of electronics knowledge - happy to dig into things, avoid getting shocked by filter caps, totally willing resolder a component here and there, but I'm def not great at actual theory or troubleshooting. I do note the red channel on the 80/100ES, as shown on the schem, is a surprisingly simple circuit, which gives me some hope I can fix this without dragging it 90 miles one-way to my tech.
Clean side of my 80ES sounds great. The dirty-channel symptoms: extremely low volume (red ch gain / master on 10/10 = volume of green channel on respective 5/1.5), sounds a bit fizzy and the gain definitely sounds way too low vs. the many Youtube clips I've heard.
The amp has two other symptoms: 1) a slight power-supply hum at idle with both channels' MVs all the way down (which may be normal for this amp, I don't know); 2) the famous pull-treble diode clipping is not working at all. I realize the latter could be a bad switch in the pot but the pots are in pretty good, non-scratchy shape as is, so right now I'm guessing it's a circuit problem corresponding to the existing issues on the red channel.
Sound clip of the clean and dirty channels here for direct comparison (I'm riding the fader to add another 10dB whenever I talk, but the amp output itself is always maintained at the same in-room volume throughout the clip).
Getting ready to tear things apart - based on aural symptoms, failing obvious stuff like broken / cold joints and visibly leaky caps, what should be my next thing to examine?
Thanks y'all.