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
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
Last edited:
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.
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.
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
And Bob's your Uncle.
Peace,
Scott
I assume you have a humdinger pot on the heater and are elevating the wiper. I would recommend the elevated bias voltage capacitor bypassing be substantial, such that its impedance relative to the bottom cathode resistor is small, and the capacitor connects to the bottom cathode resistor 0V, as that is the loop the conducted heater hum can take. Connecting to another point on the circuit/chassis will introduce any chassis noise between those points in to the bottom cathode circuit.
From heater cathode conduction leakage versus dc bias characteristics I've seen, as long as the heater DC bias level is more than about 20-30V away (pos or neg) from the individual top and bottom cathode levels (at idle) then conduction leakage is likely to be about as low as it can get.
From heater cathode conduction leakage versus dc bias characteristics I've seen, as long as the heater DC bias level is more than about 20-30V away (pos or neg) from the individual top and bottom cathode levels (at idle) then conduction leakage is likely to be about as low as it can get.
Last edited:
Thanks for the reply. The voltage divider for the low-level signal tubes is using a 33uF cap to ground very close to the first cap point. This is not a DHT amp. I am using 6CA7 as the outputs in PP. The 6CA7 heaters are sourced from an independent xfmr and will be referenced to ground on the center tap. My question is only with regards to the heater elevation of the mu-follower input section.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.