[ARC5] Re-reading Gordon White article...

[J. Forster]

> On 6 Jun 2013 at 12:43, J. Forster wrote:
>
>> ???
>>
>> I just looked at the print and L-2 is in the plate circuit of the 12SK7
>> RF
>> Amplifier, and sees the received frequency.
>>
>> -John
>
> Yes. Exactly. Weird, but obviously done for some very good reason.
>
> I would really like to know what that reason (or reasons) might have been.

Maybe your setup is introducing extra capacitance?


> One other factor here that brought this to my attention was that I was
> "finding" the peak in the
> RF input circuit of a 1.5 - 3.0 MHz receiver the other day (when I
> suspected that a previous
> hacker had modified the coils), with all the tubes removed, and found that
> the peak in the
> tuning of the RF stage is at least 100 KHz LOWER than the dial reading,
> yet with everything
> in place and operating, the RF peaks in the correct place.

That says extra capacitance.

> I had connected my signal generator to the antenna connector, and had
> connected my
> 'scope to the grid pin connection on the RF amplifier tube socket, then
> adjusted the signal
> generator frequency for a peak in the signal on the grid. The peak is
> actually quite sharp too.

It should be. It's a lightly loaded LC.

-John

=============
>
> Ken W7EKB
>
>