----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Tuesday, October 11, 2011 9:12 PM
Subject: [Drakelist] Drake TR-4C Fil. Vol. Response To
Comments
T0 WB6KBL: All the tubes in the TR-4C have indirectly
heated cathodes, so I don't know if I will get extended tube
life.
I had originally thought that lower
filament voltage would have resulted in lower electron
transfer but this would only apply to a
directly heated cathode (I think).
However, with indirectly heated cathodes, the lower filament
voltage will result in lower wattage
heating the cathode (about 4.75%
lower).
However, like W1ES/4 says, 'fire it
up and see what power comes out'.
Once again, thanks for all the comments, they made
interesting reading and I always learn something.
Bob ZL2AAQ
During WW-2 RCA ran ads (see 1943 ARRL Handbook)
showing a chart of tube life vs: filament voltage. The ad
states that plain tungsten filaments can be run at 5% below
rated voltage for double the life. It states that thoriated
tungsten or coated cathode heaters can be run _as much as_
5% below rated voltage for extended life but with some
reduction in output. As the output falls with age the
filament voltage can be increased. At the time tubes were in
short supply so increasing life was highly desirable.
In this case you have just about 5% reduction. Several
suggestions have been made about how to get exact voltage. I
suppose the choice is a matter of economics. I think if the
performance of the transmitter is acceptable on the slightly
lower voltage I would just run it that way.
BTW, I hear Radio New Zealand nearly every night on
11,725khz, strong, but with some rapid fading. I wonder
where this transmission is actually beamed.
--
Richard Knoppow
Los Angeles
WB6KBL
[email protected]
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