[Central-Electronics] 10A crystal location

[k6jek]

That is very interesting.  Moving the crystal to the top of the chassis is probably a bad idea since CE went to some trouble to move it underneath.

I have a first-three-months-of-production 20A.  They completely junked the oscillator I have, switched tubes, changed the circuit entirely after three months.  It was the first product change they made.  I need to rebuild to the later circuit before I do much else.

But let me give you an idea of just what drifter this thing is.  I did several long tests with controlled room temperature and regulated AC supply.  I gave it a five minute warm-up then started measuring every 10 minutes

Time	Drift in last ten minutes
10		-9	
20		-46
30		-46
60		-26
90		-12
120		-5

Cabinet off, chassis raised off table

Time	Drift in last ten minutes
10		-16
20		-11
30		-5
60		-1
90		0
120		1		
		
Dramatically better.  

I think rather than install a crystal oven it might be good enough just to get some air to the circuit.  First though, I'm going to rebuild to the later version

Thanks,

Jon

On Sep 9, 2011, at 10:01 AM, Merv Schweigert wrote:

> Had an early 10A and the Xtal was on top of the chassis,  just about right over the
> position it is in the 20 a underneath.
> Merv K9FD/KH6
> 
> Have a 20A I need to start working on and your xtal problems have me wondering ...
> 
> 
>> Where is the 9 MHz crystal on the 10A, above the chassis or below?
>> 
>> I notice a huge difference in drift of the 20A oscillator when I give the rock a little air.  Out of the cabinet with circulation under the chassis, the drift just stops dead after a few minutes.  Rock solid.  With the cabinet on it drifts like leaf in a stream.
>> 
>> I also noticed the mounting holes for the bracket holding the crystal are spaced just about right for a crystal holder, maybe exactly right.  I wonder.  Would moving the crystal above the chassis (where it is in the 100V) make things a lot better?  But maybe that's where it was in the 10A and they moved it underneath for a reason.
>> 
>> Which brings me to my question.  Was it up top in the 10A?
>> 
>> Thanks
>> 
>> Jon
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