[time-nuts] Inside of FT1200-100

Bob Camp kb8tq at n1k.org
Wed Nov 23 14:36:18 UTC 2016


Hi

…. but … you might *build* one of those oscillators.

The Dewar flask OCXO thing died out many decades ago. The main 
reason was size. A secondary reason was the fragile nature of a Dewar 
(they don’t take well to being dropped … I have empirical evidence). 
Neither one of these issues is particularly significant for a Time Nut basement
project. Since they tend to be a bit on the big side, super dense PCB’s are 
not a major advantage building them. The same auction sites that will sell 
you questionable OCXO’s will sell you nice working Dewars as components
for your build.

Bob


> On Nov 23, 2016, at 8:33 AM, paul swed <paulswedb at gmail.com> wrote:
> 
> Chris enjoying the pictures. Most likely I will never run into one of these
> oscillators. But it is nice to know that you have gone "where no man has
> gone before". Star Trek? Not sure.
> Regards
> Paul
> WB8TSL
> 
> On Wed, Nov 23, 2016 at 1:45 AM, Christopher Hoover <ch at murgatroid.com>
> wrote:
> 
>> A Wiha nutdriver set later and I'm in:
>> 
>> https://goo.gl/photos/SDHtvgFmftQq6vYJA
>> 
>> See the last two pictures.
>> 
>> I will disassemble the board stack and work out some schematics next.
>> 
>> Thanks everyone.
>> -ch
>> 73 de AI6KG
>> 
>> On Nov 20, 2016 5:19 AM, "J. L. Trantham" <jltran at att.net> wrote:
>> 
>> Christopher,
>> 
>> Enjoyed the pictures.
>> 
>> You might want to look at these items on theBay.
>> 
>> 381408412092
>> 
>> 311736541103
>> 
>> I've had the same issue and broke down and bought a set of these small nut
>> drivers.
>> 
>> Good luck.
>> 
>> Joe
>> 
>> -----Original Message-----
>> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of
>> Christopher Hoover
>> Sent: Saturday, November 19, 2016 11:45 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Inside of FT1200-100
>> 
>> tl;dr: I've made some progress and have the1200  oscillator core out of the
>> dewar:
>> 
>> https://goo.gl/photos/SDHtvgFmftQq6vYJA
>> 
>> 
>> 
>> I got some 5 thou brass stock and worked it between the rubber sheet and
>> the dewar.
>> 
>> That seemed to help but it was insufficient free things up -- I busted off
>> the unused solder lug trying to pull the core out with it.
>> 
>> Having not a lot to lose, I took a chance that the screws going into the
>> TO-23 went into threaded holes (rather than being clearance holes with nuts
>> inside).  This was indeed the case.
>> 
>> With two 6-32 threaded rods into the TO-23 threaded holes and and an
>> appropriately machined piece of mild steel bar stock suspended across the
>> case <https://goo.gl/photos/1pfiN2GX3WxYCSbg8>, I was able to easily get
>> the oscillator core out of the dewar by evenly tightening the the nuts on
>> the bar.    Really easily -- I might have been able to pull it out by just
>> pulling on the bar stock.  I don't know if the shim stock shenanigans were
>> even needed.
>> 
>> Despite running out the three sloted screws on the "top" around the
>> circumference,  I'm not into the inside yet.   I don't have the  right
>> thin-walled socket to remove the nuts at the opposite end.
>> 
>> I found an epoxy covered hole on the top.   It is/was under the green blob
>> midway between 1 and 2 o'clock in this picture here <
>> https://goo.gl/photos/
>> iHbSbqwBiKD7NRfJ6>..  There was something blue and
>> at this point crumbly underneath it.   Not sure yet what, if anything, is
>> beyond all of that.  I'm hoping for a trimmer cap.  :-)
>> 
>> -- Christopher.
>> 73 de AI6KG
>> 
>> 
>> 
>> 
>> On Mon, Sep 26, 2016 at 9:24 PM, Chuck Harris <cfharris at erols.com> wrote:
>> 
>>> Back when I was going to work on mine, I was thinking of prying the
>>> rubber away from the aluminum oven with something like a feeler gauge,
>>> but also using some naptha (lighter fluid) to help release any
>>> adhesive...  I didn't get around to doing it, but that was the way I
>>> was going to progress.
>>> 
>>> -Chuck Harris
>>> 
>>> Ed Palmer wrote:
>>>> 
>>>> 
>>>> On 2016-09-26 10:00 AM, Christopher Hoover <ch at murgatroid.com> wrote:
>>>>>>> 
>>>>>>> You might be able to slide something like a feeler guage down
>>>>>>> between
>>> the
>>>>>>> oven and the rubber blanket to break the oscillator free.  The
>>>>>>> oven
>>> on mine
>>>>>>> is a plain metal cylinder.  This way, the rubber sheet should
>>>>>>> protect
>>> the
>>>>>>> Dewar from your feeler guage.  On mine, the mounting bolts for
>>>>>>> the
>>> 2N3792
>>>>>>> transistor both have ground lugs.  I think I see them on yours.
>>>>>>> You
>>> could
>>>>>>> hook something through the ground lugs and use that to pull the
>>> oscillator
>>>>>>> out of the rubber sheet and then remove the sheet later.
>>>>>>> 
>>>>> Thanks Ed,
>>>>> 
>>>>> I think the rubber sheet on mine is against metal.  I haven't yet
>>>>> seen
>>> the
>>>>> glass dewar.
>>>>> 
>>>>> The adhesion is huge.
>>>>> 
>>>>> Do you know if the holes opposite the 2N3792 are threaded?   If they
>>> are, I
>>>>> might try running the screws out and using those holes with longer
>>> screws
>>>>> as my pull points.    I can't pull on the lugs hard enough -- I've
>>> tried.
>>>>> 
>>>>> -christopher.
>>>>> 73 de AI6KG
>>>> 
>>>> Yes, you have seen the Dewar.  The silvery ring that's outside the
>>> rubber is the top
>>>> of the Dewar.  What you have to do is unstick and unfold the rubber
>>> starting from the
>>>> open area in the center.  Work your way outward.  The rubber is only
>>>> 2
>>> or 3 mm
>>>> thick.  Once you completely clear the rubber out of the way, you'll
>>>> see
>>> the edge of
>>>> the oven.  The TO-3 transistor is mounted on top of the oven assembly.
>>> Once you can
>>>> see the edge, you have to slide something like a long feeler gauge
>>>> down
>>> along the
>>>> edge of the oven to break it free from the rubber.  Work your way
>>>> all
>>> around the
>>>> oven.  It's about 85 mm long.  It'll still be stuck on the bottom,
>>>> but
>>> you might be
>>>> able to pull it free.
>>>> 
>>>> When I took mine apart, I ended up tearing off all the rubber at the
>>>> top
>>> and then
>>>> cutting out that ring of hard foam to get at the Dewar so I could
>>>> smash
>>> it more.  I'm
>>>> guessing you'd rather not do that! :)  But sacrificing the rubber on
>>>> the
>>> top might be
>>>> okay, if you have to.
>>>> 
>>>> Sorry, but I don't know if the mounting holes for the transistor are
>>> threaded or
>>>> not.  In any case, since the oven and Dewar are bonded to the
>>>> rubber,
>>> you're pulling
>>>> on the Dewar when you pull on the oven.  Not a good plan until you
>>>> break
>>> the oven
>>>> free from the rubber.  Those Dewars are built in a rather fragile
>>> manner.  Your
>>>> typical home Thermos is much more robust.
>>>> 
>>>> Ed
>>>> 
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