The quote feature isn't working for me for some reason.
re: Cathode Bias
That's one of the confusing things I noticed. This amp is fixed bias. Upon further examination of the front panel, I noticed there is no presence control on the Hiwatt version. I built this circuit into a head that originally was JCM800/JMP style with a 6V6 power section. It has Gain-Vol-Treble-Mid-Bass-Presence so no alterations to the panel were necessary. I find the presence pretty useful since it can cut or boost (in theory anyway) so I'll keep that. The only major change I made (other than a new turret board/circuit) is to use a smaller PT. It had 660VCT (330-0-330) which, for SS rectified 6V6s, that's a little much. I have a Stancor 520VCT (260-0-260) Tweed Deluxe PT and that just puts it in a better range IMO. I couldn't find any specs for the power transformer other than one offered by TAD that's claims a secondary voltage of 250. I'm guessing they mean 500VCT (250-0-250) which is slightly lower than what I'm working with.
I did start looking at schematics for the DR103, DR504, etc. on EL34 world and noticed the trend of using a very sizable bypass cap (100-150uF) for the input preamp stage and then a 47nF bypass in the next one. I guess that's to grind the input of the 2nd stage and then trim it down. Pretty much the antithesis of a Marshall.
re: Different tube - ecc81 vs ecc83
I did try that initiallly. I put a 12AT7 in the PI and a 5751 in V1. The difference in gain was much more subtle than I expected. After staring at the schematic and looking at various other Hiwatt schematics, I decided to try cutting the second stage out entirely since none of them had that much heat on the front end. That's the way it's sitting on my bench at the moment. It sounds more 'normal' like that. I want to try to get somewhere in between. I don't mind some preamp distortion but it was a little much the way it was. I have amps that do the clean thing very well so I'm a little torn. My objective here is to put together a lower volume gigging amp. 5E3 is not enough, DC30 at 1/2 power is a bit much. This one shows potential since it's barely 13W clean on my scope. I'm wondering how much difference it would make to change the tone stack over to something more like the DR504 or if that would be a waste of time. The 100k between the slope resistor and ground is not something I've ever seen before and it's hard to say what it's purpose is. I didn't find it on any of the Hiwatt schematics I looked through.