Universal Load Line Calculator question

[mountainhick]

Hmm, I may be doing this wrong... Been using the Universal calculator, but also just found this one, the "Power stage" Calculator, which is pertinent for my current projects as it gives cathode resistor value. https://www.vtadiy.com/loadline-calculators/power-stage-calculator/


3 Questions:

1- Based on Rob's bias calculator, I've been entering plate voltage in the Universal load line calculator as plate pin minus cathode resistor drop. Is this correct for Anode?? On reviewing the instructions. it actually says V+. So is that B+, or voltage at the tube plate pin, or plate minus cathode resistor drop?

2-And Screen voltage? Voltage at the tube pin? Subtract cathode value?

3- And then the cathode resistor recommendation, his schematic reference shows individual resistors on each PP tube, so for combining, halve the value for parallel?

 

[YellowBoots]

So is that B+, or voltage at the tube plate pin, or plate minus cathode resistor drop?

Plate voltage minus cathode voltage. Also known as Vak (voltage between anode and cathode)

2-And Screen voltage? Voltage at the tube pin? Subtract cathode value?

Same as plate. Vg2k is voltage between screen and cathode.

And then the cathode resistor recommendation, his schematic reference shows individual resistors on each PP tube, so for combining, halve the value for parallel?

Not positive on this. His schematics don’t seem to show cathode resistors. The red dot bias point corresponds to Vak as defined above, so if you are cathode biasing, you need to add the bias voltage to the Vak (V+) to get the necessary B+ supply voltage. Same for the screen supply.

 

[2L man]

Loadline is for one tube so for two tubes which use combined cathode resistor the needed resistance is half. Individual cathode resistors keep tubes cathode bias current balance closer but one more resistor and bypass capacitor cost bit more and need more room on circuit board and few minutes longer construction time. For hobbyist building amp for own use it can be better option especially when tubes sold as balanced sometimes are not balanced to voltage/current the amp prefer.

Mr Amato should have used Vak (instead of V+) which Andred brought up!

 

[mountainhick]

Fantastic, thanks guys! Finally understanding this thing!

Mr Amato should have used Vak (instead of V+) which Andred brought up!

And I assume Vg2k, also as Andrew said?

 

[YellowBoots]

Fantastic, thanks guys! Finally understanding this thing!




And I assume Vg2k, also as Andrew said?

I never fooled around with his cathode resistor calculator. Looks he doesn’t include screen current in his cathode current. You can expect his cathode resistor value suggestion to be 5-15% high depending on the tube and time of the zodiac. Always order a couple values up and down because you will invariably experiment to find the sweet spot. Good luck.