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

[AKLDGUY .]

We've been told that the frequency shifts unacceptably when the rig
is keyed, which might lead to the conclusion that the problem lies with
the transmitting stage. However, it may be that it's the receiver that is
running off frequency and nothing's wrong on transmit.

It's suspicious that the problem exists whether the transmit tube is a
6AQ5 or VT1. This points the finger at the two receiver stages.

They do not depend on the 20V bias battery "B", because their grid
returns (terminal 3 of both T1's) is connected to S2, the ground side
of the filament line.

So the bias battery is employed only on transmit. So, how are those
two tubes biased?

With S2 closed, both filaments are at +4V with respect to S2 and the
grid circuit. The grids are therefore biased negative with respect to
their filaments. This is a standard configuration, so long as the
filament battery is connected the correct way around.

The filament battery polarity is critical. I suggest that Dave double
check it. Tubes operating at positive grid bias would likely throw the
receiver way out of proper operation.

73 de Neil ZL1ANM


On Sat, Feb 11, 2017 at 2:56 PM, arc5 at ix.netcom.com <arc5 at ix.netcom.com>
wrote:

>
>
> Sent from my Doofuss Phone.
>
>
>
> ------ Original
>
>
> Just to confirm: you're using 3 x 6AQ5, triode connected?
> ______
>
> With the link-coupled tank coil, triode-connected 6AQ5 in a bayonet mount
> for RF and two 01A for audio.  With loop, three 01As.  01A Will not
> oscillate with the tank coil, but will do so easily with the loop.
>
>
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