So, the cabinet is hand-built by a highly capable builder from the uk and it is flawless.
As far as transformers go, i opted for the exceptional IGPW ones.
Electrolytic capacitors are F&T and Sprague Atom. Resistors are NOS Allen Bradley carbon composition resistors in selected places, Dale and 1watt carbon film. Pots are 24mm Alphas. As far as tubes go, i used three Tung-Sol reissue 12AX7s in the preamp, a JJ EZ81 in the rectifier and a matched pair of JJ EL84 in the power amp.
Also, critical for the sound of the amp is the speaker. Since due to weight and portability restrictions i wanted this to be a 1x12" design, i was looking for a speaker that would provide the necessary depth that most open-back 1x12" cabs lack. After much research, i settled on a british-made Celestion G12H30 55Hz. The difference from the more usual G12H30 75Hz is that this has a somewhat lower voicing, which makes it fuller and less bright than its brother. The original amp is supposed to lack bass and be somewhat bright and seeing how the regular G12H30 75Hz is considered probably the best speaker for this amp, the 55Hz speaker seemed like the perfect candidate.
I tried to keep this amp as original as possible so i kept mods to a minimum. However, i couldn't help but make the following changes. First of all, i rewired the Hi input of the Normal channel. On the original amp, both inputs of the Normal channel are identical - each goes to a triode of the V1 12AX7 tube. It seemed like a waste to have two identical inputs on the Normal channel, so i rewired the inputs so that the Hi input transfers the input signal to both triodes of the V1 12AX7. The triodes by the way are in parallel. That makes the amp sound fuller and adds a little more gain to the sound.
The second mod was adding a post-phase inverter master volume (PPMIV). Although not as effective as in its older brothers, the PPIMV allows you to dial just a moderate crunch sound at more reasonable volume. I used a stereo linear 1M pot with 1M resistors and it turned out great.
As far as the sound goes, the Normal channel is very organic and creamy and it overdrives wonderfully. This is a blues and rock machine, no doubt about it. The Tremolo channel is a little brighter and cleaner and has a very cool sound of its own. The tremolo also is very deep and intense and adds spice to the sound - very unique. The speaker really matches the amp very well as the sound is very full and deep and not bright at all. Overall, the amp combines elements of the finest british amps - it is jangly like a Vox but with a Marshall voicing - and i can finally understand what all the fuss is about!
Update: I have been playing the amp loud more and more lately and as a result found the PPIMV no longer necessary, so it was removed. At the same time, the well-documented EL84 buzz sound started to be more apparent as volumes went higher, and as such a solution had to be found. In this case what worked without altering the sound of the amp was the "Paul Ruby" zener mod - in my case a 12V Zener in series with a 1N4007 in each tube was enough. I also experimented with the "Chuck H" mod while at it but the result didn't suit me very much, as the amp became a bit more well-behaved in the process. :)
The amp was still exhibiting some buzzing when played loud so the final solution was adding a corrective filter. After a lot of experimentation, I settled for a pair of 0.0022uF/630V capacitors and 3.9K/5W resistors, forming a composite filter of 7.8K and 0.0011uF. Two 8.2M/0.6W resistors were wired across each of the capacitors for better balancing. The textbook solution would require around 1.3 times the primary (so around 10K of composite resistance) but the off-the-shelf capacitors were either too obtrusive or too subtle. This specific combination allowed me to get rid of a big portion of buzziness without sacrificing any of the high end response and making this lively amplifier sound like there's a blanket over the speaker.
