My friend got a HiWatt Custom 50 (model # DR504) from his dad. It had some problems in the past where it would keep burning through fuses so they put it away for a while. We replaced the tubes and fuses and got it to work, but after about 10 minutes of playing one of the EL34's plates would start glowing bright orange. If we kept playing any longer it would probably start glowing red...
We followed some instructions and soldered in a bias trim pot to adjust the bias back down to the factory value of -36V as per the schematic. But the one power tube still kept glowing orange after a few minutes of playing. I've tried swapping the tubes around, its not a problem with one of the tubes, only one side of the power amp is making the tube glow too hot.
Any ideas on what else I can do? Any more values to measure beside bias voltage?
Schematic we used: http://www.drtube.com/guitamp.htm#HiWatt (DR504)
We followed some instructions and soldered in a bias trim pot to adjust the bias back down to the factory value of -36V as per the schematic. But the one power tube still kept glowing orange after a few minutes of playing. I've tried swapping the tubes around, its not a problem with one of the tubes, only one side of the power amp is making the tube glow too hot.
Any ideas on what else I can do? Any more values to measure beside bias voltage?
Schematic we used: http://www.drtube.com/guitamp.htm#HiWatt (DR504)
