I rewatched the 6LU8 build looking for a round 2 project. I forgot that it was built as a power amp requiring a preamp.
In addition, I also have seen/heard of these compactrons being used in stand alone or integrated amps.
I looked up the specs for 6LU8 and the triode at 155v and biased at 2 volts is really no where near the sections max plate dissapation of 2.5 watts.
I suspect that one could use a different resistor froom teh plate of the pentode to the plate of the triode to drop the plate voltage to 250v instead of 155v. Any suggestions for values? I will attempt to calculate them, but a hint or two, or even do not do this!!! would be helpful. I would like to build it this way, looking for a little more power than the 6BM8.
Roger
One last item.
I hace not found the BOM and final schematic for this amp anywhere. The project does not show up under your 'projects' tab.
Roger
This is an integrated amp (note the volume control and look at the input sensitivity on the analog discovery 2 testing) and shouldn't need a pre-amp at all to drive it. And most "pre-amp"/driver tubes are used no where near their max dissipation. the output tubes on the other hand are. The plate to plate resistor is the local negative feedback, not for setting the voltage on the plate of the triode. You also need a largish voltage drop across the plate load resistor on the input triode or else you end up with zero voltage amplification in that section of the amp. I've found that about 1/2 of the B+ on the plate of the input tube works well.