• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

help on power supply issues and more!

Hey everyone. I am building a preamp for recording to my computer. The main idea is this:

cap input power supply with filter choke after first cap. 330 VDC after complete filter stage.

mic input (transformer) w/pad
line in (guitar/instrument) w/pad

-> EF86 gain stage as pentode
-> 6DJ8 mu stage

Also, I want to take the output, amplify it, rectify it and feed it back to the EF86 screen grid for a basic compression circuit.

Now, my main question now is, after the choke I have a bleeder resistor to get the critical inductance down to what I have (9 Henrys) which means (30 mA * 330 VDC). I got that formula from an old ham radio book my dad gave me. Does that make sense? So, that means a 10k bleeder resistor right off of the 330 VDC. That thing gets damn hot. Is this OK?

Now, I'm wondering if I can get any opinions at all about my main preamp idea. As far as tube choice or whatever. I was thinking an all tube preamp ('cept for the diodes) but I'm probably going to rectify and regulate the heater supply. And what about this, a current sourced EF86 (small signal pentode)? Has anyone current sourced a pentode? I've looked through the internet for this but nothing.

Anyway, please let me know what you think and any help would be greatly appreciated! Thanks!!!!

- Matt Mitchell
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