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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.
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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.
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I made the amplifiers (of which I still have right here)
trying both the separate and tied heater - cathode
combinations.
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I used common Omite chokes and some home brew
chokes in the circuits. Both amplifiers did their tasks
and are now in standby storage.
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I didn't notice much operational difference using
the heater/cathode connection combinations. 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..? There's a reason
out there somewhere that I must have missed?
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skipp
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: Rich said:
> It is my opinion that the heater should always be connected
>to the cathode and the heater should float -- unless one has a
>freebee supply of new tubes.
: I agree with that sentiment - even if you have a supply of
: free tubes!
: 73
: Peter G3RZP
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