[Milsurplus] Prc-6 frequency stability

[Al Klase]

Robert,

I'd make sure I understood how the radio worked, before I started 
unsoldering any crystals.  If it's anything like a PRC-10, the crystal 
controls the local oscillator of the receiver.  I.e., the oscillator 
runs continuously at 51 +/- the IF freq.  The receiver's frequency 
discriminator is then used to AFC a free running oscillator for transmit.

Check whether it's working OK on RX either by putting a counter on the 
oscillator, or by listening to a signal generator.

Once you get past the simple stuff like all the tubes being lit, you 
need to read the schematic, and go for the throat!

Al

On 8/3/2012 1:21 PM, Bruce Gentry wrote:
> If all the components in the oscillator circuit are good, I will make an
> educated guess  the crystal is bad.  If the quartz is contaminated it
> can be extremely unstable or stop oscillating altogether and act as a
> capacitor. The oscillator could then free run anywhere the oscillator
> coil tuning takes it and drifts to.  A good crystal in the PRC-6 should
> be within  a few hundred cycles of it's labeled frequency. Almost all
> PRC-6 crystals are soldered closed, you can heat the can and it will
> come off.  As long as the conductive plating and leads to the quartz
> slab in good shape, and it isn't chipped or broken,a careful wash with
> warm water and detergent followed by a rinse with distilled water
> usually  gets an old crystal up to par.  Clean out the can as well,
> make sure the slab and leads can't touch the can, and resolder
> carefully. You should not need to use much solder to re-seal it. I have
> had very good luck with this.
>
>        Bruce Gentry KA2IVY
>
> Robert Newberry wrote:
>> I have a prc-6 that no matter how many times I bring it on freq it likes to
>> drift. Today testing it I had it drift up to 51.16. Also it would drift
>> down to 51.1. Also radio is rocked for 51.000. I know these were used with
>> radios that had front ends that were "50 wide" but it seems like it drifts
>> quite a bit. Is this normal?
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/