[time-nuts] Source of Rubidium Lamp for Efratom FRK

[Bob Camp]

Hi

At least the “common wisdom” always was that the replaceable lamps all came 
out of the same production process. There may have been enhancements as 
time went on, but the lamps all *looked* the same. There also is very little change
in the circuits that use them. 

The observation made earlier by others still holds - there is no real guarantee that
your gizmo has a bad lamp. They get pretty black and still work OK. There are a LOT
of other things that can age out / wear out / go bad in one of these gizmos. That’s not
to say don’t replace the bulb. It’s more to say that having a second working Rb might have
some other benefits …..

Bob

> On Jul 31, 2015, at 10:04 AM, Mike Niven <mfniven at ymail.com> wrote:
> 
> Thanks Bob and Chuck for the comments.  As Bob says, the lamp is easily replaceable (just unscrews) and the service manual gives the procedure.  Maybe I'm too worried about how long the lamp is likely to last but the lamp voltage was below the range stated in both the Efratom and Racal manuals.  The lamp itself certainly works but is a bit blackened.  I had hoped that Corby's procedure for rejuvenating lamps might do more than it did for this particular lamp - maybe I chickened out too early in the heating process, but I was monitoring the local temperature with a thermocouple at over 150C consistently.  Anyway, I have asked Sematron in the UK whether a replacement lamp can still be had.  If it is available at $300-500, it is really not economic as the whole Racal 9475 cost a lot less.  Mind you, I did put in a fair amount of work repairing both the Racal main unit and the FRK to get the system working.  So, probably the best way of getting a spare lamp
> is to try and pick up another whole FRK and hope that its lamp still has some life in it.  Anybody know whether the same lamp was fitted to other Efratom Rb sources?  This would widen the search somewhat.
> 
> Mike
> 
> 
>> On 30 July, 2015 11:40 Bob Camp" <kb8tq at n1k.org> wrote:
>> Hi
>> 
>> In the (unique) case of the Efratom “light bulb” cell, you can indeed pop them 
>> out and replace them. Been there / done that with the (then) factory guys involved.
>> The new bulbs were sold as replacements and did indeed fix the problem of
>> a dead bulb. About the only added work involved was to re-adjust the frequency
>> after it had burned in for a few weeks. Repeating that adjustment process as it was
>> done then would be a bit tough with no Loran :) I still have the Austron, apparently 
>> it was well enough cared for as a demo in the UK that it’s survived all these years. 
>> 
>> Bob
>> 
>>> On Jul 29, 2015, at 11:49 PM, Chuck Harris <cfharris at erols.com> wrote:
>>> 
>>> Hi Mike,
>>> 
>>> The Rb lamp voltage is just a guide.  If your Rb isn't working, then it
>>> is important... If it is, it is just a guide.
>>> 
>>> If your bulb is clear, and it is glowing, it is probably also working.
>>> 
>>> I seem to recall from HP's descriptions of how their 5065 was made
>>> that the lamp, and filter cell are a specially matched set.  Just any
>>> lamp is not necessarily going to work with any filter cell.
>>> 
>>> -Chuck Harris
>>> 
>>> Mike Niven wrote:
>>> Thanks for the comment Bob.  Tracing Efratom through the ages, I see they are now
>>> Microsemi.  I wonder whether they will still have a lamp for such a geriatric Rb
>>> source and at what price - probably more than the cost of the complete Racal
>>> 9475? I will follow it up anyway as I hardly ever see working or scrap FRKs for
>>> sale in the UK. --------------------------------------------
>>>> On Tue, 28/7/15, Bob Camp wrote:
>>>> 
>>>> Hi
>>>> 
>>>> The Efratom bulbs have a “magic mix” of gas in them. The only place I have ever
>>>> bought them is direct from Efratom. They were fairly expensive back in the
>>>> early 90’s …
>>>> 
>>>> Bob
>>>> 
>>>>> On Jul 28, 2015, at 9:56 AM, Mike Niven <mfniven at ymail.com> wrote:
>>>>> 
>>>>> Would anyone know of a source of the Rubidium bulb fitted in the Efratom FRK
>>>>> (and probably other FRx) standards?  I have repaired and refurbished my Racal
>>>>> 9475, which is fitted with the older style FRK (not -H or -L) module.  It is
>>>>> working properly at present but the lamp voltage is down to 5.5V, which is
>>>>> below the stated minimum of 6V.  I have tried rejuvenating the bulb using a
>>>>> hot air gun, as described by Corby, but this has had no obvious impact. Hence,
>>>>> I have little feel for how much life the existing lamp has left and a spare
>>>>> would be good for my peace of mind.
>>>>> 
>>>>> Many thanks.
>>>>> 
>>>>> Mike
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