>
>-
>While constructing 80 & 170Mhz triode amplifiers
>for a research project (some time back), I had
>reason to contact Bill Orr with questions. One of
>said questions was to ask why one must tie the
>heater and the cathode of the 3cx400a7 triode to
>one side of the heater. From memory, this was
>suggested in a data sheet I had at the time.
>-
>Other than "smart practice," he wasn't able to give me a
>concrete reason. Memory of that moment has been in
>my noodle for some years.
>-
Dispite the fact that Mr. Orr was well liked, he seemed to lack a
concrete understanding of RF amplifiers. Terry Gaiser, W6RU apparently
came to the same conclusion after a number of conversations with him.
>I made the amplifiers (of which I still have right here)
>trying both the separate and tied heater - cathode
>combinations.
>-
>I used common Omite chokes and some home brew
>chokes in the circuits. Both amplifiers did their tasks
>and are now in standby storage.
>-
>I didn't notice much operational difference using
>the heater/cathode connection combinations.
The difference is when there is a HV arc to gnd. ,
>Might
>be the power level I was working with, the type of
>tubes or I just got lucky. So why is it a common
>must-do to tie a side of the heater and cathode as
>one in some types of tubes..?
To prevent breakdown of the cathode-heater insulation during a major
glitch.
>...
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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