JURB
Super Member
Fixed one by the seat of my pants. Owner is enlightened about electronics somewhat. This was last week and I got busy with other things and forgot some tings but my problem has to do with R74 and R75 in the power supply, there is conflicting info on this. I clearly see the value of the one, the one is like 2.7K. IIRC R75 was burned up and the owner found the value by getting an image off of Google. I installed the resistor and it works.
However we are not sure we did right here. The resistor is fed off a 100 volt lytic, and that side is 108 volts, the other side starts at almost that and then drops as the tube warms up. Now, it puts out the same on the tube output as the other output. Owner is happy.
However I am at a loss to explain how this happened. What I saw is the tube retaining clip was undone. I suppose it is possible that due to some freak happenstance it shorted out, but am not sure it could do this. It is 2.7K and the supply is 100 volts. That means it can only give it about 4 watts, it is a 2 watt resistor. In normal operation the replacement is only dissipating a bit under 200 mW.
It is logical to assume the plate load resistors are higher than the 2.7K which seems to just decouple the power supply line. Reduce hum, whatever. So if the tube shorted out it would not mean a dead short to the supply.
The owner had applied that anti-rattle stuff to the top lid of the thing and thought that it hit the top of that filter cap, thus causing the problem. However I found that the stuff he used has a non-conductive coating, which while I DID pierce it with my DVM probes, had been intact as far as I know. I found the filter cap to actually have continuity to the + side of the supply, BUT THAT IS BEFORE THE BURNT RESISTOR !
Anyway, can you get anything on these things ? My Google searches turned up nothing. Are they all secretive about it like Roland which I have made two accounts with which did absolutely nothing for me ?
However we are not sure we did right here. The resistor is fed off a 100 volt lytic, and that side is 108 volts, the other side starts at almost that and then drops as the tube warms up. Now, it puts out the same on the tube output as the other output. Owner is happy.
However I am at a loss to explain how this happened. What I saw is the tube retaining clip was undone. I suppose it is possible that due to some freak happenstance it shorted out, but am not sure it could do this. It is 2.7K and the supply is 100 volts. That means it can only give it about 4 watts, it is a 2 watt resistor. In normal operation the replacement is only dissipating a bit under 200 mW.
It is logical to assume the plate load resistors are higher than the 2.7K which seems to just decouple the power supply line. Reduce hum, whatever. So if the tube shorted out it would not mean a dead short to the supply.
The owner had applied that anti-rattle stuff to the top lid of the thing and thought that it hit the top of that filter cap, thus causing the problem. However I found that the stuff he used has a non-conductive coating, which while I DID pierce it with my DVM probes, had been intact as far as I know. I found the filter cap to actually have continuity to the + side of the supply, BUT THAT IS BEFORE THE BURNT RESISTOR !
Anyway, can you get anything on these things ? My Google searches turned up nothing. Are they all secretive about it like Roland which I have made two accounts with which did absolutely nothing for me ?
