Tube DIY Asylum: Some news: 811A on the Hammond 1628SE by Jim Doyle

I lashed one of these up on a breadboard. Need something to
do while I await the outcome of my job search. :)

This is part of a bigger project to consume a bunch of spare
parts left over from a few years ago. The end target goal is to
use the 1628SE as a plate load rather than OPT and use a pair of
Ni pinstripe MQ parafeed transformers. Also, I will be choke loading
the CF driver to improve its linearity.

This initial prototype sounds really really good... What more, I am
using AC heating of the 811A. With a humbucking potentiometer spanning the filaments, I can null the hum down inaudible on 98dB eff speakers.

This is a very easy circuit to build out too. Classic 6SN7 gain
stage. The only weirdness is the Class A2 driver stage. :) I'm
looking forward to picking away at measuring performance and distortion at the 811A grid during October before wrapping the
project up. But, whats cool, is that this is a very easy to do
project and more people should try the 811A. Key being the fact
that you can get away with AC filaments and the buggers are $20/ea
new.

Sound wise it is very direct and very powerful. The amp itself
should do 9W but I need to adjust R3 and R5 to go full power.
I expect significant improvements going parafeed. I know the Hammonds
blow out their HF response at 13kHz or so. FYI, the 811A at 100mA
isnt even sweating yet. But it does throw heat. This is most definitely a winter amp. :)

-- Jim