Bias supply and Rg1

[Chuck H]

That's pretty much what I was thinking except I hadn't considered going full wave. I like the 100k "safety" resistor addition. Valvewizard is a good source. And FWIW I looked into it a little and I see that many ab1 KT120 circuits are using 100k bias feed resistors. You could go lower than that for insurance of course and the max 14.7k bias node resistance makes it easier to use a relatively low value for the bias feeds I did a quick CAD sim and it looks like steady bias voltage will take about 1 second. Better than many bias supplies.

[g1]

Yes, bias till max 70% power dissipation and it may double it. Some datasheets published the ratings for different power dissipation.

I don't know where the 70% comes from in your example data sheet. They show for above or below their maximum rating of tube (27W Wa+g2 of tube rated for 25W Wa).

[catalin gramada]

That's a typo , should read 17w instead 27w that seems impossible for a 25w tube, of course.

[catalin gramada]

Yes, bias till max 70% power dissipation and it may double it. Some datasheets published the ratings for different power dissipation.

Anode plus Screeen dissipation is above or below 35 Watts. Max Anode + Screen Dissipation is 42 + 8 = 50 Watts, so 35/50 = 70%

[hylaphone]

That's pretty much what I was thinking except I hadn't considered going full wave. I like the 100k "safety" resistor addition. Valvewizard is a good source. And FWIW I looked into it a little and I see that many ab1 KT120 circuits are using 100k bias feed resistors. You could go lower than that for insurance of course and the max 14.7k bias node resistance makes it easier to use a relatively low value for the bias feeds I did a quick CAD sim and it looks like steady bias voltage will take about 1 second. Better than many bias supplies.

Cool, thanks for doing the sim!

[hylaphone]

One more question if I may - I was planning on using 2x series 1N5408 on each leg for the B+, for some safety margin with the voltage and current demands of this amp. For the negative/bias side, am I ok with two 1N4007 as shown?

[Helmholtz]

For the negative/bias side, am I ok with two 1N4007 as shown?

Merlin Blencowe (http://valvewizard.co.uk/bridge.html) suggests that single 1N4007s should only be used up to a winding voltage of 290-0-290.

[hylaphone]

Merlin Blencowe (http://valvewizard.co.uk/bridge.html) suggests that single 1N4007s should only be used up to a winding voltage of 290-0-290.

Hiding in plain sight! Thanks again.