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R: [TCML] help with biasing a tetrode for VTTC
Normally, when I work with a tetrode, I put a resistor connected from HV supply, the same that go to the upper side of tank circuit, to the screen grid. This pin will be grounded through a bypass capacitor (2,2 4,7nF) close to tube filament ground.
I choose the value of the resistor so that with the maximum HV voltage, the screen voltage does not exceed the data sheet value.
In this way I obtain more result than a tied grid operation. With small tube I use a separate transformer to feed the screen grid, so that also with small HV voltage from variac, I have the full amplification from tetrode.
Vladi
Vladimiro Mazzilli
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-----Messaggio originale-----
Da: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] Per conto di Rick
Inviato: mercoledì 29 dicembre 2010 3.41
A: tesla@xxxxxxxxxx
Oggetto: [TCML] help with biasing a tetrode for VTTC
I've been studying the websites of Steve Ward and John Freau in an effort to put together a VTTC. The vacuum tubes I have on hand now are tetrodes (4-400A style), and I am not clear on what I need to be doing to bias the screen, and/or grid. Perhaps I would have been better off starting out with some triode tubes...
If I connect two such tubes in parallel, will I be alright with one filament transformer matching the electrical specs for the particular tube, or does each tube require its own plate transformer and a different connection scheme? Pardon my ignorance on the subject.
I note that these tubes were intended to be used with an air-cooled socket. Any ideas out there on cooling the tubes? Would a muffin fan be sufficient, or do I need a more directed airflow up from the base of the tube?
Any advice is greatly appreciated.
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