{Collins} Re: cRYSTAL



Here is a possibility. 

I noticed when I was 15 years old(I'm 68 now) that some radios had this problem.  The 'unused coil' that was next to another coil, when switched out of the circuit, became resonant to the frequency of the coil next to it and it "sucked all the RF" out of the circuit...... ROFL.....

Actually, if a circuit near another one, when it's switched out, may become pretty close to resonant too.   I would scratch a couple of turns of the coil of the problem coil and solder them together, changing it's resonance. 

This happened in the DX 100 when switched to 15 meters.  Reduction of drive to the finals. The driver coil had the 160 meter to 15 meter portion of the coils shorted out but it still resonated closely to 21 MHz.  Scraping a few turns on the 160 meter coil and shorting them out with solder caused the problem to disappear.

Fixed more than one DX100 this way.  Think about it.  That could be the problem here too.  Sometimes ingenuity is needed to solve the problem. 
Bob  W5UQ




Garey Barrell wrote:
Glen -

There seems to be something associated with the 15M band crystal in the 75A-4 that causes them to "fail".  Similar to the 40M crystal problem in the Drake 2-B receiver.  Those two are the ones that fail, while you hardly ever hear of others failing in the same receiver.

I had a problem with the 15M crystal in my 75A-4 years ago, and found that if I mistuned the 20M crystal position that the 15M position would then work.  It was then possible to retune the 20M adjustment and everything was fine.  I could never find out why, but at least two other A-4s with "bad" 15M crystals responded to the same procedure and were working years later, as is mine.

The 2-B situation is the result of the oscillator circuit used, which operates as a fundamental oscillator on some bands and as an overtone oscillator on other bands.  The 40M crystal is "on the edge" dividing the two modes and often fails.  In most cases, replacing the 6U8 oscillator tube with a 6EA8 gives enough gain to "save" the original crystal, as proven in many 2-Bs over the years.

Has anyone else seen or figured this out, or was it all just a bad dream!??!?!

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>



Glen Zook wrote:
I got my 15 meter crystal from International Crystal. Make sure that you get the proper one.  There were 2
different frequency ranges used depending on whether
or not it was an early model or late model.  Someone
had replaced the 15 meter crystal in the 75A-4 that I
traded for several years ago and had put in the wrong
version.  Therefore, I had to get the correct one.

Glen, K9STH


--- JWKIMBALL@xxxxxxx wrote:

I need a 15 meter crystal to get my 75A-4 going. Any
suggestions as to  where would be appreciated.

 
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