[R-390] Scale varies band to Band

[Bob Camp]

Hi

Indeed a crystal is just a  chunk of quartz in a fancy enclosure. The R-390 crystals that have failed on me have had features in them. My guess is that either the radio or the crystals got dropped. Once the fracture propagated far enough the resistance went high enough to stop the oscillator. 

One thing that does bring up - as the crystal oscillator tube wears out, the weakest crystal in the bunch will go first. I've never actually tried swapping out tubes to see if it brought "dead" crystals back to life. It might be an interesting experiment. Gm is what counts in this case, so a tube tester should be able to verify good / bad tubes. 

Bob

On May 13, 2013, at 6:06 PM, Gordon <gordon at n6wk.com> wrote:

> Hi Bob,
> Well, That explains it. Sure would have been nice if they had put trimmers in there though. LOL
> I don't have any "Extra" Crystals, so looks like it will be a while before I can find all that closely match..hi hi..
> Another Question, What makes a crystal go Bad..ie (Stop working)? Isn't it just a piece of Quartz ?
> 
> Gordon N6WK
> 
> 
> On 5/13/2013 2:51 PM, Bob Camp wrote:
>> Hi
>> 
>> A *long* time ago I ran into the guy who designed the oscillator deck in the R-390A. When asked "why no trimmers?" the answer was - It wasn't in the spec. Put another way, they could do everything they needed to do without them, and they cost money ….
>> 
>> If you can come up with a big enough pile of crystals, you can sort them into groups that match fairly well. It's a time consuming process and should be done tin the radio you will be using them in.
>> 
>> Bob
>> 
>> On May 13, 2013, at 4:42 PM, Gordon <gordon at n6wk.com> wrote:
>> 
>>> Is it normal for the scale to vary a couple Kc's band to band?
>>> For example, If the Calibrator is dead on 7.500 on the 7 Mcs band, is it normal for it to be maybe on 8.502 on the 8 Mhz band and maybe 9.497 on the 9 Mhz Band?
>>> I do not see any trimmers to bring each crystal dead on. Am I missing something?
>>> 
>>> 
>>> Thanks,
>>> Gordon
>>> N6WK
>>> 
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