[ARC5] Your deaf receiver.

[AKLDGUY .]

Brian cannot be using a 12SF7 in his BC-454. The pinout for the 12SF7 is so
vastly different from that of the 12SK7 that even the heater pins are
different. But he has already told us that all tubes heat up to normal
temperature.

So a 12SF7 cannot have been fitted, unless some hacker has wired the heater
pins for 12SF7 and messed up the wiring of that socket's other pins.

73 de Neil ZL1ANM


On Wed, Sep 28, 2016 at 3:40 AM, Kenneth G. Gordon <kgordon2006 at frontier.com
> wrote:

> The 12SF7 is ONLY used in the AN/ARC-5 receivers at the 2nd IF, and its
> base diagram is
> very different from the 12SK7. Plugging one into a BC-454's, or an ARA's,
> second IF stage
> will "confuse" many of the connections in that stage.
>
> If a 12SF7 is being used in this BC-454, it is no wonder the gain is
> down!!!!!
>
> The 12SF7 has an added diode inside the tube. This is where the AGC
> voltage is taken off
> so that the BFO can be either on or off without effecting the AGC circuit.
>
> The AGC circuit in the AN/ARC-5 receivers was much improved over that in
> the earlier
> receivers.
>
> Ken W7EKB
>
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