[Milsurplus] MY BC-375 Resotration

[Mack McCormick]

David,

I am using T-29 as the VFO. That goes into the resistor slider tuned
network (low Q) (see the picture) which provides an 18 ohm load for the
T-29. Since a wire wound resistor has both resistance and inductive
reactance I simply resonated the slider resistor with a capacitor to form a
parallel tuned circuit. The slider on the resistor is connected to the grid
of the first 211 tube which then makes it a buffer amplifier to feed the PA
second 211. I broke the connection to the first 211 where it receives
feedback through a capacitor for the PA with the first 211 was acting as an
oscillator. Driving with 30W from the T-29 I get about 85 watts out of the
BC-375.

The audio is being driven through a small mixer with equalizer into the the
standard mic input on the BC-375. I did remove the internal carbon mic bias
inside the BC-375.

Behind the control panel is a relay to key the T-29 and mute the BC-348.
Also is the small mixer. The relay is keyed by the BC-375.

These two changes (the only two I made) are very easily reversible in less
than 30 minutes.

Let me know if you have other questions or would like to see a schematic of
the input circuit.

73,

Mack
W4AX

On Sun, Nov 13, 2022 at 15:43 David Stinson <arc5 at ix.netcom.com> wrote:

> Wow!  That's some lovely work.
> Please give us details on how you're feeding
> drive to the MO stage, and how you are driving
> the audio.  Excellent, good sir.
>
> On 11/13/2022 2:00 PM, Mack McCormick wrote:
> > The transmitter and tuning units were located new in the box from the GE
> > factory in 1934. I’m using a T-29 transmitter as a VFO to prevent the
> > BC-375 from FM’ing due to using a MOPA oscillator. I built the custom
> > furniture with inspiration from the Western Historic Radio Museum. I
> > have about 120 hours into this project and it is working perfectly! I
> > plan to have it on the Old Military Radio Net next Saturday.
> >
> > https://photos.app.goo.gl/iyYRv1cEQafeCrrj7
> > <https://photos.app.goo.gl/iyYRv1cEQafeCrrj7>
> >
> > 73,
> >
> > Mack
> > W4AX
> >
> > --
> > 73,
> >
> > Mack
> > W4AX
> > https://www.qrz.com/db/w4ax <https://www.qrz.com/db/w4ax>
> >
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-- 
73,

Mack
W4AX
https://www.qrz.com/db/w4ax
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