[Central-Electronics] 20A drift, breaking my heart.

[Jim Candela]

Jon,

    I have been wondering about updating the 20A 9 Mhz oscillator. Here 
is my idea, use a solid state TCXO, and interface to the 6U8 pentode 
section such that this is a class C amplifier instead of an oscillator. 
Interfacing the TCXO to the 6U8 control grid could be done with a 
transistor. Here is one TCXO possibility:

http://www.cardinalxtal.com/docs/series/CTCX.pdf

   I don't know what this would cost, but the 9 Mhz would hold pretty 
much dead on afterward. The TCXO needs 5v at 2 ma so power could come 
from rectified filament, and simple 5v zener diode scheme.

Jim
WD5JKO

On 8/31/2011 10:06 AM, k6jek wrote:
> Well shucks.  I got a bit of a handle on the drift and the thing hops on me.  It just doesn't want to be pinned down.
>
> Thanks everyone
>
> Jon
>
> On Aug 31, 2011, at 6:44 AM,<kirklandb at sympatico.ca>  <kirklandb at sympatico.ca>  wrote:
>
>> I've been working on a modern project and yes crystals can jump in frequency. These days we are using 19.2 MHz crystals as reference oscillators
>> for 800, 1900 MHz equipment. Small jumps in xo frequency cause larger jumps in the final frequency. Talking to XO manufacturers, there are many reasons.
>> Some are due to contaminates on the crystal. If the drive level changes/fluctuates, then the magnitude of the xo osc changes and can shift a contaminant particle
>> there by causing an xo freq jump. Another effect is due to how the crystal blank is mounted, ie. if it is rubbing against something.
>> There are other mechanisms inside the structure of the crystal as well.  Crystals also exhibit hysteresis effects over temperature as well.
>>
>> I am not saying that any of these are causing your drift/jumps. Just answering the question "Can they do that?"
>>
>>
>>> ________________________________
>>> From: k6jek<k6jek at comcast.net>
>>> To: central-electronics at mailman.qth.net
>>> Sent: Tuesday, August 30, 2011 10:29 PM
>>> Subject: [Central-Electronics] 20A drift, breaking my heart.
>>>
>>> I was happy for awhile but my hopes were dashed.  This old 20A was drifting a lot, still drifting about 26 Hz every 10 minutes after an hour.  I took it out of the case and propped the chassis up so air could flow underneath.  Voila! It got darned stable. After an hour drift was only 1 Hz in 10 minutes.  Drift after 30 minutecs was only 5 Hz/ten minutes. How about that?
>>>
>>> Would just a little air make it  better?  I put the 20A back in the cabinet and put the most insignificant of fans on the outside on the left pointing into the lower left cabinet vent, a 4" 240V fan running on 120.  It worked much better than I expected.  Drift was down to about 3 Hz every 10 minutes after an hour.
>>>
>>> Then tonight, while participating in the vintage SSB net it hopped, jumped  60 Hz.  What the heck?
>>>
>>> Normally I'd think this was a faulty cap, one that has a temperature sensitive fault.  But you know those caps surrounding the crystal in the 20A, C86, 87 and 88?  This early model has none of them.
>>>
>>> Is it the crystal itself?  Can they do that?
>>>
>>> Thanks,
>>>
>>> Jon
>>> ______________________________________________________________
>>> Central-Electronics mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/central-electronics
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:Central-Electronics at mailman.qth.net
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> ______________________________________________________________
>>> Central-Electronics mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/central-electronics
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:Central-Electronics at mailman.qth.net
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>> 		 	   		
>> ______________________________________________________________
>> Central-Electronics mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/central-electronics
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Central-Electronics at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
> ______________________________________________________________
> Central-Electronics mailing list
> Home: http://mailman.qth.net/mailman/listinfo/central-electronics
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Central-Electronics at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>