[time-nuts] My Racal-Dana 1992

Charles P. Steinmetz charles_steinmetz at lavabit.com
Sun Dec 18 18:00:58 UTC 2011


Ed wrote:

>My 04E must be less stable than yours.  I was monitoring a fully 
>warmed-up Efratom FRK rubidium and saw a drift of ~ 0.04 Hz (i.e. 40 
>counts) over two hours after I turned on my 1992 from standby.  Are 
>more than one type of oscillator used for option 04E?  Mine is a model 9462.

There are actually two Racal part numbers that you sometimes see in 
documentation as being used for Option 04E -- 404386 and 454879.  The 
9462s in the US military contract 1992s that I have seen (pretty much 
all of the 1992s one sees in the US are from the mil contract, IME) 
are marked "9462 454879."  I have not seen an oscillator marked 
"404386," so I do not know if these are Model 9462 oscillators or 
another model.

As with any crystal oscillator, there is no doubt a range of both 
stability and warm-up drift in the 9462s you find, but IME not a very 
large variation.  (I'm assuming that you clocked the warmup after the 
1992 had been in standby -- plugged in with the red power button "on" 
-- for a week or more [preferably for a month or more].)

An oscillator with greater warm-up drift will not necessarily be less 
stable, after warmup, than one with less warm-up drift.

>How did you replace the switch guts?  Where did you get the parts?

They pull straight out the front, after removing the key cap.  We 
bought new switches from TOKO (the only OEM for that part), but they 
were retired from production around 20 years ago and I have not seen 
any available in the pipeline for years now.  Unfortunately, the 
parts units you find for sale invariably have bad switches.  I have 
more than once tried to use switches from a donor unit to repair a 
1992, and they have all promptly failed during post-op testing.  In 
one case, six successive switches failed within five presses after I 
installed them (that was way back before I figured out that you can 
replace the innards from the front, when I was desoldering and 
replacing the switches whole).

>I hadn't thought about cleaning causing the switch failure.  I just 
>assumed it was old age with different brands or lots of switches 
>being made with different recipes for the rubber and therefore 
>different lifetimes.

That was my original thought, too, but I believe the data indicate 
otherwise.  Soldering and cleaning appear to be the next most likely culprits.

>I haven't seen a capacitor with detents.  Could the fine adjustment 
>be a multi-turn pot?

I assume that is the case -- that is exactly what it feels like -- 
but I have not disassembled a 9462 to see.

David wrote:

>Strange, the fine adjustment on mine doesn't have any detents.

Not surprising -- I assume many of the parts were obtained from 
multiple sources, and if detented multiturn pots of the appropriate 
value were out of stock, it would be natural to replace them with 
their much more common non-detented counterparts.  Or perhaps Racal 
specified a regular, non-detented pot and when a vendor shipped them 
detented pots by mistake, they used them anyway for one lot of 
oscillators and I happen to have a couple of those.

The labels on 9462s indicate there were several revisions.  I do not 
know what is different internally between revisions.

Best regards,

Charles




   






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