Hey all,
I've been doing some tinkering with the 6EM7 and 5K output loads in v2.0 mono-blocks.
For starters, "Cbias" is now 1000uF 100V.
With 119vac line voltage, I've changed "Rpsu" from 680R to 3.2K and "Rbias" from 620R to 1K. This resulted in an operating point of 203Vp-k, -34Vg and 32.8mA for triode #2. I think lowering "Rpsu" to 3K will get me to my goal of 210Vp-k, -35Vg, 34mA and about 2W output.
The driver is now at 104Vp-k, -1.29Vg and 1mA.
Next step will be to install a C4S-SR-C4S regulation for the 6EM7 driver stage, shunting about 5mA through triode #1 from the 6DN7. All of that should draw about 10mA and get the driver to around 170Vp-k, -1.6Vg and 2mA.
Then, something similar for the output. HV secondaries will be paralleled.
I didn't get how to empirically calculate the -Vbias or the resulting output operating points, so there was a lot of trial and error, and huh??? But I figure the first step is getting that to be stable at -35V, and I've almost got that. Whew! I now see that all the PSU current flows through "Rbias", so its just Ohms' Law. 1K will give me 35V @ 35mA, and when the circuit is drawing its full 70mA, "Rbias" will be 500R.
Update #1: HV secondaries now paralleled, "Rpsu" is now an MQ RGC-6 + 1.5K 5W = 1680R, "Rbias" is now 1.3K 5W. Output quiescent OP's are about 250Vp-k, -44Vg and 34mA.
Update #2: C4S installed in both mono-blocks and Rk of driver reduced to 990R, which results in Vk of 1.78v/1.8mA and Vp of between 150 and 200V. "Rd_psu" changed to 10K/10W and "Rbias" changed to 1.2K 5W. I will need to go through all my 6EM7s to see what the general average is. Given that the B+ (driver) is at 275v, I think a Vp of 170-180v would be best.
Example of measured operating points: Driver 148.5Vp-k, -1.78Vg and 1.8mA. Output 239.3Vp-k, -43.3Vg and 36mA. Heater voltages are 5.9v with 6EM7 and 6DN7 and 6.5v with just the 6EM7.
Update #3: Wiring modified to make "right" side of each mono-block the driver and the "left" side the output. R1 of C4S changed to 220R and Rk changed to 1081R. 6DN7 driver biases at 138Vp, -4.3Vg and 4mA. Slightly lower gain but very nice sound. 6SN7 drivers should roll in to this circuit.
