813 Push Pull E-Linear Amplifier

After the previous 813 amplifier, I wanted to try another 813 amplifier using the parts I had at hand that was a bit simpler. I was attracted to an E-Linear type design that I'd seen on Audio Asylum being championed by Douglas Piccard but adapted to the parts I had to hand.

Initially I tried a D3a front end but that proved difficult to get stable and it was pushing the D3a near all its maximum ratings. I didn't have any other pentodes to try but I did have a stash of 6N6P which I could use in cascode as the driver. These proved to be well matched and the end result came up very close to the sim. Using a CSS in the tail of the driver LTP meant it was easy to adjust the top anode voltage.

I was limited to about 30k for the 813 grids which reduced the gain of the driver as this was in parallel with the 47k anode resistors of the driver. Initially I tried an interstage transformer secondary as a grid choke to see if it would work but the CL resonant circuit produced a bump in the lower frequencies that could be heard. I am now using a cheap grid choke.

Below is the schematic I'm trying at present. It still needs some work but it's a good starting point