I have completed the 6BM8 build, and I am impressed with the sound. However, with the transformer wired up for 125vac, my pentode plate voltage is only 203-206vdc (tubes in). If I wire the transformer for 115vac, the pentode plate now sees about 240vdc. I would like to get the voltage right at 220vdc.
First, is it necessary? I know it is not because it works, but I would like just a bit more power. Second, is it possible? I would think that voltage drop resistor might help, but I am not sure which one I should change.
Any advice on the approach would be helpfull. I DO have psuds2.
Roger
It's going to make a little more power with the plate at 240V. These can handle 300V on the plate so that's not anything to worry about, it's not nessasary to have the B+ exactly as spec'd and it will vary based on the transformer, wall output voltage etc.
What is important is to make sure the current across the output pentode doesn't exceed specs as far as watts of dissapation. What are you seeing as far as voltage on the cathode of the output tube at 240V B+? The design I used is running the tube pretty close to it's design limits. I'm not sure there is much that will get a noticable amount more power from this amp and the 6LU8 might be better suited to your needs? Hope you had fun building this little amp!