[time-nuts] Restoring GR 1120-AB Frequency Standard

Wed Aug 20 05:42:26 EDT 2008

Russ
Do you have a photo, would it be possible to build? I have a few flasks of
mercury and a few 10's of thousands of mercury wetted relays that some could
be cannibalized for electrodes. The trick here is how thin is that column of
mercury. My guess the thinner the column, the finer the resolution or the
more it will travel with a small temp swing. Better yet, possible to cut
that thing open and fix it.
I know that's more time than it's worth.

Another thought, if the contacts have corroded in the mercury, perhaps from
contamination, would it be possible to "burn" the contamination off.
Thinking of excessive voltage/current. Perhaps making it arc internally.
Trick would be to limit current not to explode the thing, perhaps using a
charged capacitor. Just a thought.

Oh, do you have the whole rack, all dividers and the clock? I bet the old
clock alone is worth a thousand bucks today. Seems like it was driven by 1
KC. My old standard was complete, a 5 or 6 foot rack and came out of an old
Hamerland Radio plant.

phil

----- Original Message ----- 
From: <wa3frp at aol.com>
To: <time-nuts at febo.com>
Cc: <fortime at bellsouth.net>
Sent: Wednesday, August 20, 2008 4:16 AM
Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard

>
> Phil,
>
> I didn't believe that the thermoswitch was the problem, at first, chiefly 
> because of the simplicity of operation. Eventually, after checking wiring, 
> a carbon resistor that is in series with the thermoswitch, and components 
> around the inner oven control circuitry, I removed the thermoswitch to the 
> bench.
>
> After hooking up to a ohmmeter and using a 60 watt light bulb as the heat 
> source, I found that I could duplicate the
> a pulsating open / close as before. I first focused on the bulb leads and 
> eventually completely removed the old leads and rebuilt each one and did 
> all new soldering under magnification. The problem remains the same.
>
> I'm ready to move on at this point noting that this component failure has 
> me stumped and that the fault is most likely internal to the thermoswitch 
> (as strange as this seems). Years ago, when I first saw how internal 
> temperature worked using the mercury thermometer switch, I remarked that 
> it was one component that would never fail. HA! That statement came back 
> to haunt me.
>
> Best,
>
> Russ
>
>
> -----Original Message-----
> From: phil <fortime at bellsouth.net>
> To: Discussion of precise time and frequency measurement 
> <time-nuts at febo.com>
> Sent: Wed, 20 Aug 2008 3:45 am
> Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard
>
>
>
> Russ,
> Also could it be a cold solder joint on the tubes connections, possibly 
> look
> good but have a high resistance. That could account for an intermittent as
> you are describing. Sometimes we overlook the simplest of things.
> Phil
>
>
> ----- Original Message -----
> From: "phil" <fortime at bellsouth.net>
> To: <time-nuts at febo.com>; <wa3frp at aol.com>
> Sent: Wednesday, August 20, 2008 3:26 AM
> Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard
>
>
>> Russ,
>> In other words, you sound like you are not 100% sure it's the switch.
> A
>> shame you couldn't graph voltage and current going to the switch as it
>> cycles. Is it possible a cap or something else is intermittently
> failing
>> in
>> the circuit. Again I'm assuming with that resistance there is
> something
>> between it and the heater. Though I had one, I don't think I ever
> looked
>> inside the thing.
>>
>> I have seen some similar units (I think what you have) that use an
> almost
>> paper thin column of mercury. I would guess that is how they can
> achieve
>> the
>> fine resolution/precision.
>>
>> Phil
>>
>>
>> ----- Original Message -----
>> From: <wa3frp at aol.com>
>> To: <time-nuts at febo.com>
>> Cc: <fortime at bellsouth.net>
>> Sent: Wednesday, August 20, 2008 2:34 AM
>> Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard
>>
>>
>>> Phil,
>>>
>>> The details of the thermoswitch failure are not completely clear.
>>> Intermittently, the mercury column will pass the 78C point without
>>> causing
>>> circuit closure. Instead, a pulsating open / close with an internal
>>> resistance of 50K - 300K is observed. Circuit closure eventually
> happens
>>> at a temperature above 82C. Once an external failure, i.e. lead
> wiring,
>>> was ruled out, I used a borrowed microscope to view the internal
>>> structure
>>> of the thermoswitch. Unfortunately, this did not reveal the failure
>>> source.
>>>
>>> Russ
>>>
>>> -----Original Message-----
>>> From: phil <fortime at bellsouth.net>
>>> To: Discussion of precise time and frequency measurement
>>> <time-nuts at febo.com>
>>> Sent: Tue, 19 Aug 2008 9:33 pm
>>> Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard
>>>
>>>
>>>
>>> Neville,
>>> good answer. Perhaps the original poster could supply a photo of his
>>> switch,
>>> perhaps more suggestions could be made. I think we had an old
> gr-1100 at
>>> one
>>> time, it was a 100kc unit. Needless to say it was scrapped years ago
> and
>>> I'm
>>> sure it's been melted down and sent back to the usa in tin cans or
> cars
>>> by
>>> now! I'm curious as to how the switch failed. I'm assuming it was a
>>> sealed
>>> unit.
>>> Phil
>>>
>>> ----- Original Message -----
>>> From: "Neville Michie" <namichie at gmail.com>
>>> To: "Discussion of precise time and frequency measurement"
>>> <time-nuts at febo.com>
>>> Sent: Tuesday, August 19, 2008 7:46 PM
>>> Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard
>>>
>>>
>>> Hi,
>>> this is a second attempt at an answer, the first seemed to evaporate.
>>> Mercury-in -glass thermometers have formed the basis of a system of
>>> thermostats
>>> used constant temperature systems of very high performance.
>>> A major producer of contact thermometers was Jumo (maybe German).
>>> These thermometers had a thin wire that went down the capillary and
>>> contacted the mercury at the set temperature. The system could be
>>> accurate to
>>> 0.005 degree. The control algorithm is alien to modern EEs but used a
>>> large thermal mass and a fixed rate of heating to produce a slow
>>> temperature ramp.
>>> Fast response by the thermometer switching kept overshoot down to
>>> millidegrees.
>>> A cycle time of 5 or 10 seconds kept a very low amplitude temperature
>>> ramp running up and down
>>> with mean temperature held quite close.
>>> Locating the thermometer close to the heater caused a little over
>>> control which reduced overshoot and cycle amplitude.
>>> The thermometers had up to 30 mA run through the wire, but more
>>> modern units reduced this to 1mA.
>>> If the tip is corroded on your thermometer contact, maybe a higher
>>> resistance measuring circuit may
>>> still operate reliably.
>>> Good Luck with the unit,
>>> Neville Michie
>>>
>>>
>>>
>>>
>>>
>>> On 20/08/2008, at 9:17 AM, Mark Sims wrote:
>>>
>>>>
>>>> I suspect the only place you would find a replacement themoswitch
>>>> is in another unit. I also doubt that any current mechanical
>>>> switch will be anywhere near stable and accurate enough.
>>>>
>>>> I stand by my original comments: Built a solid state functional
>>>> replacement in the same form factor as the original unit. It will
>>>> be hidden inside the oven assembly where only you will know of the
>>>> dastardly deed that you did. If you ever find a replacement
>>>> switch, you can install it and bask in its originality. Until
>>>> then, bask in its solid state patch enabled oscillatude.
>>>>
>>>> A non-original part that restores a device to operating condition
>>>> is far superior to a dead unit... particularly if the part is not
>>>> visible. There are lots of zillion dollar antique cars winning
>>>> best-of-show with modern internal engine components (not to mention
>>>> bondo and fiberglass under the paint).
>>>> ----------------------------------------
>>>>
>>>> _________________________________________________________________
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>>>
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>>
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