heater elevation ground point

[scott17]

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?

[ryuji]

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

[scott17]

Originally Posted by ryuji

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.

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.

[ryuji]

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.

[scott17]

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

[trobbins]

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

[scott17]

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.

[ryuji]

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

[scott17]

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

[scott17]

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!