[TenTec] Failure mode for Omni VI oscillator assembly

[Ken]

Pete -

I've got an Omni 6+ with an oven controlled oscillator that seems to fit 
your description of a cooked out circuit.  Every 6 months or so I have 
to re-tune the oscillator to keep on frequency.  I would like to replace 
the OCXO with a TCXO but I understand Ten Tec no longer offers a mod 
kit.  Therefore I am very interested in how you made the mod.  What DIP 
package did you use and how did it perform?  Any hints or advice you can 
give me would be appreciated.  I love my Omni 6+ but am irritated with 
the frequent re-tuning of the master oscillator.  If I can successfully 
mod my rig, I will provide my old OCXO to anyone who wants to 
investigate it's failure.  Thanks...

Ken, K9PGC



On 2/11/2017 10:34 AM, Peter Bertini wrote:
> I've read that these old ovenized elements "cook out" and become unstable
> after many years of reliable service. The rig starts to exhibit drifting
> and requires frequent retuning to keep on frequency.
>
> I recently replaced a few with modern TCXO DIP 20.000 MHz oscillator
> packages; and I dissected one of the defective original ovenized crystal
> packages.
>
> It seems to be a very simple circuit.  The crystal is heated by what
> appears to be a plastic package transistor, and the temperature of the
> crystal is monitored by a thermistor that is epoxied to the crystal case. I
> surmise the  thermistor adjusts the forward bias on the transistor
> accordingly.
>
> In the unit I opened, I discovered that the thermistor was no longer
> attached to the crystal case; thus the thermal tracking would no longer be
> accurate.   I'd guess this could be fixed using a tiny dab of heat
> conductive epoxy or other adhesive?
>
> I'm just passing this along in case someone cares to experiment and report
> back on whether this is a viable fix or not.
>
> regards
>
> Pete
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec