Hybrid Shenanigans

[Sheldon]

I just put this thing together. Test results to follow. The output end is based on the Zeus design by Susan Parker. My transformer driven version is described in the last few pages of her long thread. Zero Feedback Impedance Amplifiers

I wanted to make a tube driven version, so I can drive it with anything, as the transformer version requires a low impedance driver, and well, just because. Nothing like taking a perfectly good design and driving it into the ground.

Here's the amp and power supplies for the driver. Each channel has a separate filament supply. The extra windings for the filaments and tail supply are wound on the driver power transformer.

The power supply for the output section is in the following post.

Sheldon

[Sheldon]

One supply per channel. The weird design is to create a feedback loop to stablize the bias as the output devices warm up. As the bias current increases, the reference for the bias shifts more negative. The dropping resistor on the return of the main supply is sized so that the bias doesn't drift.

Sheldon

[jkeny]

Hi Sheldon,
I still haven't gotten around to using the Lovoltech parts you sent me & I see you are using them here.

Looking forward to your test results.

As you are doing a bit of shenanigan & you seem to enjoy off-beat design - did you ever consider the 6AR8 tubes for phase splitter duties & vol control in this design? A modified BDT preamp ala John Swenson

[Sheldon]

Here's some distortion measurements at about 1 watt output. Looks like I could still do a little work on the output section power supply.

I haven't worked with those tubes, though I seen that design and it looks like it would be cool to try.

[Sheldon]

BTW, I made a few errors in the original schematic. Corrected here:

[Sheldon]

Also simplified the bias supply. I may simplify further and remove the temperature compensation. It stabilizes fine after it warms up.