[R-390] Re: 200kc crystals

[Drew Papanek]

Roger  wrote:

>If we can find some 200KHz in the new smaller can sizes they could be 
>mounted into the HC-6 cans.

>The HC-6 have hollow pin leads and much easier to rebuild than the power 
>supply filter caps.

And no uckumpucky to dig out!

it is quite likely that a 100 Khz crystal of the correct type would lock the 
multivibrator at 100 KHz and no modification to the multivibrator would be 
needed..  Of course, if one wanted 50 KHz  cal points then the multivibrator 
could be so modified.

I see where Mouser offers 100 KHz  electronic watch type crystals from 
several different manufacturers.  The watch crystals have a high ESR at 
resonance; they might not oscillate in the circuit of the R-390A.   However, 
they cost less than $2.00 and so might be worth a try.

For 100 KHz cal points, one could also use a crystal at some other multiple 
of 100 KHz.   As the multiple is increased, the scheme loses practicality 
because the mutivibrator free-running frequency has to be held closer to 100 
KHz.

The R-390/URR (AKA non-A) uses a 1 MHz crystal which locks the 100KHz 
mutivibrator at the 10th submultiple.  An occasional problem with the 
R-390/URR calibrator arises due to tube or component aging where the 
multivibrator locks onto another submultiple of the 1 MHz crystal frequency. 
   The result is 90.9 KHz or 111.1 KHz cal points.  That radio's calibrator 
multivibrator has a trimmer cap to enable setting the free running 
frequency.

Drew

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