P, your advice is spot on, as always, brother. How are your hummingbirds doing?
Here's what I have since I last posted (a mere 2 days ago!)
I added a pi filter after the rectifier, dropping a couple of volts but knocking down a ton of humbuzz. I made a q&d 12V power supply node out of a 100K resistor in series with a 12V Zener || electro cap. That's all fed by the 140V 138V B+.
I started messing with a breadboard and a 2N5457 to get the JFET to bias somewhat well off the 12V feed. Ended up with a 6K3 load and a 680R source resistor, just shuffling through parts using the Tillman JFET Booster preamp values as a starting point. Once I had a reasonable bias point I soldered that mess in between the input jack and the old input node. 1uF tantalum cap DC blocker.
Then I played a little!
So: this is still a "preamp" with gain <1. But the JFET got the input level up so I could hear a bit of nice smooth grunge - I'd say the design CONCEPT is still promising. I'm going to have to get a little more serious - bust out the scope - to get much further and get a sense of the signal levels in each stage.
The "BONE RAY" tone stack is a bit different from the typical, but I think I like it. I'll see what happens when I get a chance to mess with it more. I should probably try bypassing it completely too, to see what it sounds like with that signal drop neutralized, so that maybe needs a switch?
Oh hey, wait a second - I didn't bypass the source resistor with a cap - so I have some "free" gain for the cost and effort of soldering in one cap. I'll do that tonight for sure.
It's good to be back.
I'll finish with a cautionary tale: the reason I had to put this project – all my projects! – on hold for so long, was, I let my workspace get so disorganized I couldn't find anything nor find a clear space to work. A nightmare. It took a visit from some German cousins to get me to spend TWO WEEKS cleaning up and sorting through mess, both in the "guest room"/workshop and the "pit of hell"/basement.
I found all sorts of half-baked idea carcasses in various stages of undevelopment along the way. I started off easy, boxing up another Gus Smalley ASDF that I had already completed the circuit board for, but my real target was this project, which I had never stopped wondering about. Still a challenge but finally making some progress!