heater elevation ground point
 

I am raising the heater reference voltage for my mu follower input stage by 55VDC. Is there any concern as to the ground point for the voltage divider?

why only 55v, i did full 70v for mine -- i used the same ground the filter caps to my b+ is connected to, which is connected to earth ground and my chassis(i play it safe with grounding).
used a 10 uF capacitor across the resistor that is connected to ground. part choices was mostly just what i had laying around.

theres some kind of rule of thumb that you use 1/4 of your b+ i've seen floating around somewhere. In my case of 450v B+ thats outside of tube specs so i chose 70v as a compromise

55V is adequate for my circuit. Like you said "I had (those parts) laying around." I am using a ground bus layout. First-filter ground to the low-level signal ground, and a separate first-filter ground to the output tube bias cap ground. I have grounded the voltage divider to the low-level signal ground bus. I am assuming that since the voltage divider that provides the reference voltage is very low current, that this is OK. Just asking.

your setup is similar to mine. all of my signal grounds (6 of them) combine into one wire, and that wire leads to a wire i ran from filter capacitor ground. same deal for the 807 grounds, and the 6au6 grounds. i personally directly connected my divider directly to my filter ground as it was nearby and convenient.

Cool. And your scheme worked out fine as I interpret. Thanks for the "comfort zone" reply.

Are you refering to DC raising the heater of the input triode only of the mu-follower?

Is that for minimising heater to cathode hum leakage in that triode?

Ciao, Tim

I am raising the heater reference voltage for both sections of the mu follower because in my case it is convenient and greatly simplifies the circuit. I am using the EH 6922. The heater-to-cathode rating for this tube is +/- 200V. This rating does not hold true for other versions of the 6922 or 6DJ8. The EH brand 6922 is rated like the Russian 6N23P.

keep in mind that its 200v AC, dc point is commonly 70~100v on the smaller tubes

edit: datasheet im seeing says 120v max for positive potential with reference to cathode and -50 max, for if its negative

That is not actually correct. The EH 6922 is rated +/- 200VDC heater-to-cathode voltage. I am quoting here: The 6922EH is based on the Russian 6H23Pi-EB military version of the 6922. It is more rugged and has higher ratings than other 6922/E88CC tubes. The 6922 was designed to be used in wide-band high frequency amplifiers, usually in a cascode circuit where one section was cathode fed with the grid grounded. This is where the maximum cathode to heater rating is important. I would suspect that the Russian military probably also used the 6H23Pi-EB in some pulse circuits (radar receivers), which made the higher plate voltage rating desirable.

And Bob's your Uncle.

Peace,

Scott

This tube is not a "standard" 6922 or 6DJ8. Here is the spec sheet for the EH 6922. Check it out.

Now watch the price go up. Whoops!