[Milsurplus] BC-9: A Big Road Block

[AKLDGUY .]

The key is the switch symbol above and to the left of meter M,
isn't it? How come it shorts meter M when pressed? Is there
no indication of plate current when sending?

73 de Neil ZL1ANM

On Sat, Jan 21, 2017 at 4:57 AM, David Stinson <arc5 at ix.netcom.com> wrote:

> By using an external tank coil in place of the loop and link-coupling, I'm
> getting good, sensitive receive and
> am able to get a good Watt of power
> out on 80 Meter CW.  https://goo.gl/photos/SthdKR1rmwxXkZ6z6
>
> I had this dream of making a few contacts with it during Novice Rig
> Roundup.  But now there's a big problem I should have seen coming.  Take a
> look again at the diagram:
> https://goo.gl/photos/THcWRvYScQfnp5gg9
>
> The RF stage is regenerative through the plate
> resistor, R5.  This reduces the plate voltage on
> the RF tube during receive from 120 VDC to
> 70 VDC.   To transmit, the plate resistor is shorted,
> the full 120 VDC is applied resulting in a strong
> oscillation for transmitting.  And here's the rub:  What happens with a
> non-
> crystal tube oscillator when one raises the B+
> from 70V to 120V?  Right- the transmit freq
> jumps higher by several KC.
> Some movement is to be expected, but I suspect
> that the original VT-1 didn't move as much as
> the substitute 6AQ5; otherwise the rig wouldn't
> have stayed in service for a decade.
>
> Irreversable changes are absolutely forbidden.
> Not sure how I'm going to address this.  Always
> feel frustrated if I don't get at least one QSO out
> of a rig.   Perhaps something can be done in
> the substitute tube mounting.  I'm open to suggestions?
>
> TNX OM ES 73 DE Dave AB5S
>
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