[Johnson] Pacemaker Problems

[Al Parker]

hi DAvid,
    Do you really mean the same coil is used at 0.5MHz & 4MHz with only a 
1000pf cap switched in?  Seems like an awfully wide range, 8 to 1, for one 
coil to do the job.
73,
Al, W8UT

----- Original Message ----- 
From: "David C. Hallam" <dhallam at rapidsys.com>
To: "Ed Tanton" <n4xy at earthlink.net>; "'Johnson List'" 
<Johnson at mailman.qth.net>
Sent: Monday, September 15, 2008 7:39 AM
Subject: RE: [Johnson] Pacemaker Problems


> 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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>>
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