Install sockets for adjustable gain. Stick with 6GM8 tubes. Try pete millett's DC heater supplies if you run into problems with hum.

I've only skimmed through the Rev A thread, but got the impression most hum issues were due to proximity of the transformer to the amp boards?

Well, that too. I had a fully encapsulated transformer for my EHHA, and I still encountered hum. I didn't encase it though, and the wires were a rat's nest.

Are your boards for the rev.A or the EHHA I?

I

I never had issue of hum with my builds (original or rev. A)

I preferred the BJT (2SC2238 / 2SA968) version to mosfet one.
I also recommend DC heater supply for tubes.

The original EHHA can be run with tightly twisted AC without hum. I agree on the 6GM8 and the socketed resistors for adjusting the feedback ( it changes the sonic character of the amp enough to warrant some experimentation )

Take a look at the way that steinchen set up a rotary switch to adjust gain - http://www.diamondstar.de/inventory_tubeamps.html  , I thought that was pretty nifty

..dB

Gain resistors are socketed. I think I will run the lowest gain setting ~ 7.5 or 9. I find the HE-500 I am using super ineffecient (on my Gilmore Lite with claimed gain of 6 I am at 12-1 o' clock on the volume pot, I rarely go past about 8 o' clock with Senn HD580), but still doubt I would want to go higher than 9 with my 2v source.

WRT to the open loop gain/NFB, will the amp sound more linear with a touch higher NFB?

I am a tube dude at heart, but like a clean sound.

I never had issue of hum with my builds (original or rev. A)

I preferred the BJT (2SC2238 / 2SA968) version to mosfet one.
I also recommend DC heater supply for tubes.

The boards are populated with mosfets and I think I'll stick with them, given how big a pain it is to desolder heatsinks 

Any suggestions for budget heater supply/transformers? And is there any difference to using a 12.6v 500 ma or 6.3v 1A transformer for the heaters?

Thanks for all replies all.

Don't do whatever the guy did who built mine.  Sounded like a portable amp 

I'll try  I wasn't a big fan of the one EHHA I heard, but I'm guessing it was feedback related or just not built well. Given the positive feedback of this amp with orthos I want to explore the amp myself.