[Johnson] Pacemaker Problems

[David C. Hallam]

The signal goes into the grid of the 12AT7 balanced modulators but does not
come out at the plate.  My question is why?  The way the circuit is
designed, the 80M and 40M plate circuits of the balanced modulators use the
same coil and capacitor to resonate them with the single change that a 1000
pF mica capacitor is switched in on 80M.  The 40M circuit operates at 4 MHz
and the 80M operates at 500 KHz.  The 40M output is OK but the 80M is
nonexistent.

I checked the 1000 pF capacitors with my old capacitor tester.  This thing
is so old that the calibration is no good so I can't trust any reading for
capacity.  However, the capacitors show no short, open, or leakage and read
about 800 pF.

I am going to replace the two capacitors but was wondering if there was
something else I was missing.

David
KC2JD/4

> -----Original Message-----
> From: Ed Tanton [mailto:n4xy at earthlink.net]
> Sent: Sunday, September 14, 2008 6:41 PM
> To: dhallam at rapidsys.com; 'Johnson List'
> Subject: RE: [Johnson] Pacemaker Problems
>
>
> If you have an FET oscilloscope probe, this is the very application they
> were designed for! You could see where the signal goes IN but
> does not come
> OUT, so to speak.
>
>
> Ed Tanton
>  
> website: http://www.n4xy.com
>  
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