I did - a 470k as shown in the attached. This is as built (minus the power filtering) and briefly measured.
I made PCBs for this build, and put spare pads for triode / pentode operation, differing power supply topologies, shunt feedback etc. So this schematic may not be (isn't) the optimal solution, but one I was able to do without massacring the PCB...
I made PCBs for this build, and put spare pads for triode / pentode operation, differing power supply topologies, shunt feedback etc. So this schematic may not be (isn't) the optimal solution, but one I was able to do without massacring the PCB...
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Thanks! As I said I'm thinking to do the same and I was reading here More Hybrid-Amplifier Design Briefly, J. Broskie says that if the feedback resistor is too big then there will be an early treble roll off due to Miller effect and if it gets too small it will load the driver tube. The cure for this is to increase the output impedance of the driver and he suggests a high value cathode resistor or a CCS.
There's another thing about the coupling capacitor that I can't find an answer. As is it is tailored for the input impedance defined by the grid resistor of the power tube. But the feedback resistor is supposed to decrease the input impedance so does this result to early bass roll off unless the coupling capacitor is replaced with a bigger one?
If you have the time to take some measurements could you please check those issues?
There's another thing about the coupling capacitor that I can't find an answer. As is it is tailored for the input impedance defined by the grid resistor of the power tube. But the feedback resistor is supposed to decrease the input impedance so does this result to early bass roll off unless the coupling capacitor is replaced with a bigger one?
If you have the time to take some measurements could you please check those issues?
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