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

wa3frp at aol.com wa3frp at aol.com
Wed Aug 20 04:16:46 EDT 2008


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).
>>> ----------------------------------------
>>>
>>> _________________________________________________________________
>>> Be the filmmaker you always wanted to beearn how to burn a DVD
>>> with Windows.
>>> http://clk.atdmt.com/MRT/go/108588797/direct/01/
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/
>>> time-nuts
>>> and follow the instructions there.
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.


_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to 
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.




More information about the time-nuts mailing list