screen and plate voltage

[J M Fahey]

WOW! You have discovered the problem, which I now can see before even switching anything on! But, I shall first perform the tests you requested.

14) 38 vpp
15) 42 vpp
20) 38 vpp

18) You are correct! I omitted the ground point at R2. That turret also hosts the second cathode and LDR ground in the tremolo circuit (I don't understand how it was functioning, but it was, at least for the quick second I checked). I shall install that ground presently and will be interested to perform those tests again, as well as any others you may like to see.

You're welcome
Your amp did still work (although deaf as a brick) because "R1"=820r provided a DC path for all of them, only problem was thyat power amp had 100% NFB, gain was exactly 1 (38Vpp at the output, 38Vpp at the LTP NFB input), while it should have been 1+(820/100)=9.2X

Thatīs a huge gain loss, and at a critical point.
Loss in a preamp is often not that bad, because preamps usually have excess gain to accomodate weak players and pickups, old rusty strings, poorly setup guitars, etc. , so losing 20dB preamp gain is nothing; but losing 20dB on the *power* side is a catastrophe.
The Normal channel barely worked; the Vibrato channel did not .... but again none of its fault.

Only problem is that youīll have to revise your statement in post #1:

I got everything right, and it's quiet as a mouse.

I bet now itīs like any other DR proper build

[pdf64]

The vibrato channel can't put out as high a max clean signal level as the normal channel because the 50k trem intensity pot loads down the 3rd stage's output.

[patlaw]

Juan, your expertise is amazing, as is the expertise of several other generous contributors here.

[J M Fahey]

Oh, thanks, itīs very kind of you.