[TenTec] Failure mode for Omni VI oscillator assembly

[Paul Kraemer]

There are some 20mhz tcxo modules on ebay that look like they might work
Can't beat the low price
Worth a shot
Paul K0UYA

-----Original Message----- 
From: Ken
Sent: Saturday, February 11, 2017 12:22 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Failure mode for Omni VI oscillator assembly

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
> _______________________________________________
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> TenTec at contesting.com
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