[Milsurplus] More on BC375 Tube Subbing

[Skip Frolik]

Dubose converted BC375's for use in the 2-4 MC Marine Band
along the Gulf Coast. They used 838's as the modulators.
Course they also changed out the 211 in the final to an 813
along with a better rf chain and speech amp so other "Fine
Tuning" was incorporated. Bottom line for mentioning this
is that for the most part "Most" of the 375 was kept intact
so apparently at least in the modulator stage this was a
win-win situation.
Skip
-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net]On Behalf Of David Stinson
Sent: Tuesday, June 07, 2005 11:39 AM
To: Milsurplus New mailman
Subject: [Milsurplus] More on BC375 Tube Subbing


While getting the SCR-287 ready for W5E in April, I subbed
an 838 triode in both the oscillator and power amplifier stages of the 375.
The 838 physically looks like the 211, with a more robust mechanical
structure. It costs less than half what one would pay for a NOS 211.

The 838 is a "zero bias" triode amplifier, while the 211
is a more conventional triode.  It also has a somewhat different
interelectrode capacitance.  After re-neutralizing the PA,
the 838 seemed to work just fine in the final.
In the OSC stage, it appeared to be somewhat less
stable, but I didn't really give it a proper warm-up.*

Does anyone have any thoughts on using this tube
as a lower-cost substitute for the VT-4 / 211?

73 Dave S.

* as an aside- once the 375 had run for a couple of hours
prior to the W5E event, it became quite frequency stable on 3880 KC.
After two hours, I never had to correct it again.
But then, I did hand-pick the oscillator 211 for stability,
so that may have been a factor.
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