It lives!
View attachment 101189
Everything works as expected except I have some oscillations at the top of the gain for channel 1, and channel 2 with "more" engaged oscillates almost right away.
But channel 2 without "more" has no oscillations at all. I did skip the treble bleed cap to ground at the input. That is the first thing I'll try. If that doesn't fix it I'll break out the signal gen and oscilloscope. I used zero shielded wiring and a have a couple of longer runs, I don't think it'll be too hard to track down.
It's loud as fuck, easily saturating my GT120 power amp. The Soldano X88R preamp does a 97% cut at the end, I thought that might be excessive, I'll likely get close to that before I call it done. I kind of want to see how the Sunn Model T power amp fairs before I commit though.
The preamp itself is pretty quiet, I don't hear any hum, but it will amp noise coming into it like any high gain preamp. With a Fortin Zuul+ between my guitar and amp it's quiet as can be at idle.
How does it sound? I have never played a real VH4. Also I would not consider myself to be a high gain dude. I'm into doom and heavy classic rock, with taste of spaghetti western. Like if Keith Richards worshipped the dark gods, had no talent, but also lost all ability to play from a bad car accident. Anyway...
Channel 1 (VH4 channel 2) is very crunchy like a plexi. Great for dirty mid gain sounds.
Channel 2 (VH4 channel 3) sounds great throughout it's entire gain range, a giant sweet spot I guess, the same character through the range just more until the gain knob stops turning. It has great, even unexpected, string to string definition for chords. To my ears, this is the 'at the sunset of grunge', great rock guitar sound.
Channel 2 with "More" engaged (VH4 Channel 4) is just too much. It's like chocolate cake with chocolate frosting with chocolate ice cream on the side with some fudge on top of it all, and a chocolate shake to wash it all down. It loses the nuance. I do have the oscillation, but it seems to go away when I play, but I'll hold out judgement until that is fixed.
Likely it'll sit in VH4 Channel 3 mode and rarely change.
Here's my updated schematic:
View attachment 101190
The biggest changes are the 100KA master volume pots, how the gain pots are wired (3 and 2 tied like an variable resistor), and how the bass pot is wired. I also have the treble bleed at the input crossed out for now because I don't have that in there.
I added the model I used for the power transformer, and annotated my voltages in red. My B+ supplies are very close to modern VH4s (they run just above 360V at those points). However I want them to be higher, I plan on updating my PSU Designer II model with the real data and then figuring out what the first dropping resistor needs to be lowered to get me closer to 390Vish on the supplies (what the early VH4s ran at allegedly). That would also get my elevated ground reference for the heaters higher. Closer to 70V will be good for the two cathode followers.
I concur with those decisions given my above experience.
The FX Loop is a harder nut to crack. I'm sure it contributes to the sound like the SLO FX Loop does. That is why I use the same setup as it's driver-cathode follower pair at the end of my preamp, post tone stack. I was going to tack on the X88R driver-cathode follower on all these preamps but in this case it seemed better to just stick with what's in the VH4. Adjusting the voltage divider right before the send to sum whatever the last triode pair does might be the best solution.
So you are at 3 preamp tubes, PI tube, and then power tube pair?
) I should be mostly fine with 630V for the B line and around the PI. For the cathode I will likely stay at 50-63-100V, but I prefer film there because I am allergic to polarity. I will use some known amps as a reference and try to read up more on Triode basics.
