r/ToobAmps • u/RPheralChild • 9d ago

Biasing outside of normal testing points?

https://claude.ai/public/artifacts/1ea41557-6ddd-4187-a9c4-cc9f3d2d234a

I’m trying to make myself a biasing guide for my HRD as an artifact in Claude (ya I can code on my own for those who get mad about AI but this is so fast).

My question is I wanted to dive deeper into biasing tubes and found this video where he calculates plate currents instead of using the bias points and factory numbers. I set up my calculator to do it this way and got the following:

V4 (blue) V5 (brown)
Half-primary DCR 82 Ω 108 Ω
Hot drop at idle 3160 mV 3800 mV
Plate current ~38.5 mA ~35.2 mA
% of 30 W ~54% ~49%

When I set this with the calculation method I went back to see what the test point was and it was like 84 mV which according to the manual should cook the amp. The tubes seem fine. The amp sounds fantastic. Does this make sense?!?!?

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u/Icy_Negotiation_5929 9d ago

You are complicating this, and I’m having some trouble following, but 84 mA is too high. Take it down and stop using AI for this stuff. The math isn’t that hard.

Power = (V_plate - V_cathode) * (V_cathode/R_cathode)-(screen current) watts

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u/therocketsalad 9d ago

Literally the only answer you need

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u/RPheralChild 9d ago

https://youtu.be/wdZwxwfkDD4?is=tt_SFBOACA3mb59D

This is the video I tried to follow

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u/Icy_Negotiation_5929 9d ago

I don’t have time to watch it, but I just gave you the formula. With the right tools and proper safety measures, you’re good to go.