AO-44 fun

[SILVERGUN]

You may want to add 1N4007 diode protection in for each 6CA4 anode, just in case the 6CA4 is getting old.

Have the EF86 and the triode anode voltages all idle biased up ok?  One pain with the 6GW8 (and any triode pentode) in a PP arrangement is that not only do the two output stage pentodes need to have reasonable idle current balance, but the two triodes need to sit their anodes at reasonable idle levels, otherwise the signal can start to get wacky too early.

I updated the schematic to reflect the voltages and added those diodes (thanks, I like insurance)

The EF86 appears to be fine but it looks like I have a problem with the PI voltages that I wasn't expecting. I'm only seeing 2.9V on the cathode of the PI. Nowhere near the listed value of 51V that sluckey was showing on his AO schematic.

So, it appears that my pre PI voltage divider was also dividing the voltage at the PI cathode. I'll insert a cap right after the divider and re-measure. Unfortunately I'll have to wait til later.

I confirmed this by snipping out the the V div. path to ground and now I'm seeing 44VDC on the PI cathode.

[sluckey]

So, it appears that my pre PI voltage divider was also dividing the voltage at the PI cathode. I'll insert a cap right after the divider and re-measure. Unfortunately I'll have to wait til later.

I confirmed this by snipping out the the V div. path to ground and now I'm seeing 44VDC on the PI cathode.

Bingo! The cap will fix that.

BTW, you may consider replacing the voltage divider with a 100K-A master volume.