[Milsurplus] BC-9 Loop Test: Scratching My Head.

[AKLDGUY .]

Everyone's thinking is along the line that the unit is faulty on transmit,
because the frequency shifts when the set is keyed. As I pointed out
earlier, the frequency offset may actually be apparent on receive, and
the frequency shifts to the correct one when keyed.

I am interested in meter M. I presume it was a moving *iron* type, since
that was the historical type. If a moving *coil* type has been fitted, the
impedance in the plate circuit of the detector is changed, perhaps
causing a frequency offset on receive.

Redrawn circuit:
https://photos.google.com/share/AF1QipPaz-hyQC9eOuPrWPnKAwcHXcUz7x6k2J-5N1Krbn2wR0C1zD7Anf_6C0nGE-mfRg?key=QWNoTTNGV2lwOW9uTGVoc3RjcVhBbFliVmFBN1RR

73 de Neil ZL1ANM


On Sun, Feb 12, 2017 at 2:20 PM, Hubert Miller <Kargo_cult at msn.com> wrote:

> If you look at the partial manual that was posted, mentioned previously,
> what you are describing is the SCR-77-A, the early version. Except that
> they did run it at 120 volts, not 60.
> Altho no operating instructions are there for the SCR-77-A,  it's apparent
> the oscillator is continuously running, under receive, while for transmit,
> it's keyed.  The same power level
> for receive and transmit, no receiver dropping  resistor. You can imagine
> this
> might make it difficult when more than two stations were operating and one
> was quite a bit weaker. This set did NOT have the frequency offset Dave's
> improved version exhibits.
> The dropping resistor in Dave's later BC-9 was an improvement, so-called,
> to decrease the radiating receiver level. That brought other problems,
> which maybe even are more
> difficult to overcome. But i think they "could" communicate, altho the
> stations would be chasing each other across the dial.
> -Hue
>
> -----Original Message-----
> From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
> Kenneth G. Gordon
> Sent: Saturday, February 11, 2017 4:58 PM
> To: Richard <brunneraa1p at comcast.net>
> Cc: Milsurplus at mailman.qth.net
> Subject: Re: [Milsurplus] BC-9 Loop Test: Scratching My Head.
>
> On 11 Feb 2017 at 19:44, Richard wrote:
>
> >
> > I think someone said the last change was higher voltage on transmit.
> > Some dim bulb who knew a thing or two, but not enough, probably
> > proposed it for more output, and it was accepted by a supervisor who
> > knew less.  I've seen this happen on big electrical equipment, with
> disastrous results.
> > Richard, AA1P
>
> Good thinking.
>
> So, if David dropped the 120 V feed to 60 volts (which is the maximum
> rated plate voltage for a VT-1) then removed the capacitor and 100 K
> resistor, replacing them with a piece of wire, the system may work
> correctly?
>
> Hmmm.....well, I don't see it. The "oscillating detector" will be
> oscillating at the same level of output in either case, it seems to me.
>
> THe only thing the key would be doing is bypassing the meter and the audio
> stages by a bit.
>
> David?
>
> Ken W7EKB
>
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