Screen grid resistor for 5F2-A

[Denny_A]

Other than limiting the screen grid current flow, what if any affect would adding a screen grid resistor have on my 5F2-A build? Any tonal differences or effects on other pin voltages on the power tube.

Thanks, Denny

[Bruce / Mission Amps]

Originally Posted by Denny_A

Other than limiting the screen grid current flow, what if any affect would adding a screen grid resistor have on my 5F2-A build? Any tonal differences or effects on other pin voltages on the power tube.

Thanks, Denny

If it is less the 1K ohm then it will not effect the sound much because the tube is running flat out in Class A with max current anyhow.
And, a 6V6 screen does not draw a lot of current at idle ( one or two ma probably) ... so even at 10ma to 15ma of screen current with the amp screaming, a 1K would lower the screen voltage 10v to 15v.
What I like to do on these amp types is decrease the 10K screen node resistor a little, use what ever additional screen resistor is needed (from that node to the screen lug on the socket) to keep the plate voltage and screen voltage closer at idle conditions.
That might be a 470 ohm or 2.2K ohm resistor.
Remember there will be quite a voltage drop across the output transformer secondary with high Class A idle current... that's why there is a fairly large value 10K screen node resistor... a choke installed there will have virtually no voltage drop compared to the 10K resistor and the screen will be much higher voltage then what you measure on the 6V6 plate pin/lug.
However, don't fall into the Net driven claims that the screen voltage has to be less then the plate voltage... it is not true.
Just try and keep the plate voltage, (yes plate voltage)... low enough for proper class A operation with the single 6V6 tube idling at 15 watts or less, while the plate and screen voltages are within a few volts of each other (+ or -) ... for happy tube life and a rockin' dog tone.

[Denny_A]

Bruce,
I have SS diodes instead of a 5Y3 and increased filtering (47uf,47uf,47uf,and10uf). The plate voltage is 347v and the Screen Grid is 314v. Is there a point that the screen grid voltage is too much lower than the plate voltage? I have not put a screen grid resistor in yet on the power tube (6V6).

Cathode to ground voltage measures at 19.5v with a 500ohm 5watt bias resistor. 12.77 watts at idle. It sounds good now but maybe it can be better?
Thanks!