Screen resistors and PI grid stopper on 5e3

[Ledvedder]

I'm curious to hear everyone's opinion on 470r power tube screen resistors and a 470K PI grid stopper on a 5e3 build? I see some recommendations for adding them, but I also see that it changes the overdrive character. Has anyone used either, and what is you opinion?

[Esquirefreak]

Depends a bit on how you intend to play/use the amp. In my experience, 470R screen resistors don't alter the amps character drastically, but makes life easier on the tubes, especially if pushed with higher B+ voltages.

Grid stopper on the phase inverter might be wise if you intend to drive it hard, keeping the overdrive a little less loose and avoiding blocking distortion. But then again, that's what some people like about the 5E3.

You could always tac solder a A1M pot before the PI and tune it by ear. Then, when your happy with how it sounds, just measure the resistance and put in a fixed resistor. Or put a 1M trim pot on the board and adjust whenever necessary.

/Max

[sluckey]

I put 470Ω/1W screen resistors directly on the socket.

     http://sluckeyamps.com/5e3/5e3.pdf

[pdf64]

My view is that the benefit of screen grid (current limiting) resistors becomes minimal if the screen grid HT node can’t deliver much current.
The 5E3, with its 5k HT dropper to its screen grid node, being an example of that.
It’s a rather different scenario to eg a 5E4, where the screen grids are fed from the same node as the OT CT https://el34world.com/charts/Schematics/files/Fender/Fender_super_5e4a.pdf
Or a Twin Reverb.

Low value grid stopper resistors on the screen grid may still be good practice though, eg 100ohm 1/2W for a 5E3.