Quick check on initial measurements of SE 5881 power section

[CascoSieg]

My second build - aiming for a two channel SE power section (to support stereo effects), and TBM front end. So I'm starting with just mocking up a single output channel on a board, will setup and tweak from there, eventually expanding testing, and building it into a chassis. I'm looking mainly for a clean power section, that might reach shimmery verge of clipping when pushed, but don't plan for it to clip or heavily distort.

I'm hoping for a quick check of my numbers so far on the 5881 SE power section, currently mocked up (no schematic yet):

Max dissipation should be 23W according to the data sheet.

SS rectified B+ = 338v
V(plate) = 320v

A goal of center bias and full dissipation (V^2/P) would mean 4.5k OT primary. I've got a 5k primary, which seems safe - also have an 8k primary and multiple secondaries (4/8/16), so the OT could provide a variety of loads (APD-8031H).

So, using the 5k primary I've measured:
Cathode R = 200 (with bypass cap)
V(cathode > ground) = 13.4v
Current through the tube then, should be I=V/R = 67mA , which seems within tolerances.
V(screen) = 250 (achieved with two 3-watt 22k resistors)

It "looks" like my load line is near full dissipation (21.4W) and just hitting the knee of the 0V gradient line, though I'm just eyeballing it.

Do these numbers look OK in terms of stable and healthy (tube-wise) operating window?

[thetragichero]

that's about what i got from here https://www.vtadiy.com/loadline-calculators/power-stage-calculator/
says 224r for cathode resistor but i like tack soldering on the cathode resistor so i can measure and tweak and listen. 200r seems a decent starting point imo

[CascoSieg]

Holy smokes! THAT's a handy calculator!
Thanks!

[tubeswell]

My second build - aiming for a two channel SE power section (to support stereo effects), and TBM front end. So I'm starting with just mocking up a single output channel on a board, will setup and tweak from there, eventually expanding testing, and building it into a chassis. I'm looking mainly for a clean power section, that might reach shimmery verge of clipping when pushed, but don't plan for it to clip or heavily distort.

I'm hoping for a quick check of my numbers so far on the 5881 SE power section, currently mocked up (no schematic yet):

Max dissipation should be 23W according to the data sheet.

SS rectified B+ = 338v
V(plate) = 320v

A goal of center bias and full dissipation (V^2/P) would mean 4.5k OT primary. I've got a 5k primary, which seems safe - also have an 8k primary and multiple secondaries (4/8/16), so the OT could provide a variety of loads (APD-8031H).

So, using the 5k primary I've measured:
Cathode R = 200 (with bypass cap)
V(cathode > ground) = 13.4v
Current through the tube then, should be I=V/R = 67mA , which seems within tolerances.
V(screen) = 250 (achieved with two 3-watt 22k resistors)

It "looks" like my load line is near full dissipation (21.4W) and just hitting the knee of the 0V gradient line, though I'm just eyeballing it.

Do these numbers look OK in terms of stable and healthy (tube-wise) operating window?

Yep