Millett Low mu Preamp help

[dsavitsk]

I am looking to build a slightly modified version of Pete Millett's low mu preamp. (originally here http://www.pmillett.com/lowmu_preamp.htm)

The primary change I am making is to use the Bottlehead C4S constant current sourse rather than the pentode based version Pete uses. As far as I can tell, the voltage drop across the C4S is just a few volts. Pete suggests running the plate voltage at about 150V, so I am planning to lower the B+ to about that.

Also, Pete biased the heaters up by 45V due to requirements of the el34 based CCS, but since I am not using this CCS, I am planning to not do this. In fact, I am intending to use a toriod (perhaps with SS rectification) for the B+, and a second small transformer for the heater.

Here is the basic schematic I am looking at. Can anyone offer any comments or suggestions before I get started? This will be one of my first tube builds, so even obvious comments and suggestions are appreciated.

Thanks,

-d

 

[Zen Mod]

put some 470K from pot wiper to ground-tube just don't like that grid loose ground-in case that your pot make some weird thing

elevate Uf to some DC potencial ,because you'll get less hiss and whistle from your tube ; tip-there is invisible diode between heater and cathode in every indirect heated tube and that diode is just waiting to rectify every AC gremlin near those preciouss electrodes 😉
when you put some DC distance between Cathode and heater ,lets say that mentioned diode is removed from circuit.
if you don't believe-try......then choose

 

[dsavitsk]

put some 470K from pot wiper to ground-tube just don't like that grid loose ground-in case that your pot make some weird thing

Good Suggestion. I'll definitely do that. I have also seen others using input transformers, and I may look into that as well.

elevate Uf to some DC potencial ,because you'll get less hiss and whistle from your tube ; tip-there is invisible diode between heater and cathode in every indirect heated tube and that diode is just waiting to rectify every AC gremlin near those preciouss electrodes 😉
when you put some DC distance between Cathode and heater ,lets say that mentioned diode is removed from circuit.
if you don't believe-try......then choose

I'm not sure I understand what you are saying here. Could you explain more fully