[time-nuts] Bulova crystal oscillator
kb8tq at n1k.org
Thu Sep 7 12:16:16 EDT 2017
The real fun was building those ovens, at least for the “precision” versions:
The thermostatic switches came in with a fairly loose tolerance on them. First
step was to play with a bunch of water baths to sort them out. If you wanted
something like a 0.5 C tolerance that would take a *long* time.
Crystals got tested in a chamber for turn temperature and that data was recorded
somewhere. In some cases it’s still written on the crystal holder.
The two got matched up and run over temperature. Either the match worked or
it didn’t. If it was off, they bumped up or down one bin on the switch.
Final step if the spec required it was to fine tune the gain / set by moving a tab
or screw in the vicinity of the switch. The tab or screw went to the outside of the
enclosure. You “moved the cold” to change what was going on.
Lots of fun, and lots of arguments about what to do on this or that unit.
One weak point was the quality of the switch. The ones you could afford were
bi-metal. As they wore out, the set point shifted a bit. Eventually the contacts
welded shut with predictable results ….That might have been 40 years later.
> On Sep 7, 2017, at 11:42 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> I saw something very similar, and it had a bi-metal regulator.
> Simple and effective for its time, but not very good if you care about better performance, as bang-bang regulation of slow rate isn't as good as the same crystal could do with a more linear regulation. Never the less, it's kind of nice.
> Now, I wonder where that oven went, I'd love to get it running. :)
> You always learn something. :)
> On 09/07/2017 05:30 PM, Bob kb8tq wrote:
>> The 115VAC power suggests that it dates back a ways. The 100KC frequency suggests
>> the same thing. It could easily be a 100 KHz crystal in a simple thermostat controlled oven.
>> In that case, the stability would not be anything super duper.
>> Your guess of 0.001 Hz gives a 1x10^-8 sort of number. That’s probably a good guess for the
>> set tolerance on the unit. Anything from there up to 1x10^-7 isn’t a bad guess for temperature
>> stability. Again, it’s all guesswork.
>>> On Sep 6, 2017, at 10:26 PM, Glenn Little WB4UIV <glennmaillist at bellsouth.net> wrote:
>>> I have a Bulova crystal oscillator, part number 1505869-1K, model number AMO31HP-V-1, NSN 6N5840-797-7659.
>>> The NSN tells me it is a little old and that it was a turn-in, probably repairable at some higher level.
>>> The frequency is marked 100.000000 KHz.
>>> The oscillator voltage is 30 V DC and the oven voltage is 115 VAC.
>>> It has an octal plug on the bottom with the pins marked:
>>> 1 - oven indicator
>>> 2 - A.F.C.
>>> 3 - heater power
>>> 4 - +30 VDC
>>> 5 - case ground
>>> 6 - ground
>>> 7 - heater return
>>> 8 - 100 KC output.
>>> With the nameplate listing the frequency in KHz and the case listing the frequency in Kc and the older NSN, it appears that this oscillator was made for a longer period of time.
>>> The top has two adjustments, both with a screw cover.
>>> One is freq adj and the other is output adj.
>>> Does anyone have any data on this oscillator?
>>> What would I expect the accuracy to be?
>>> The printed frequency implies, to me, that the accuracy is in the realm of 0.001 Hertz at 100 KHz.
>>> Did I miss something here?
>>> The top also shows this to be a "Generator Reference Signal".
>>> Any insite appreciated.
>>> Glenn Little ARRL Technical Specialist QCWA LM 28417
>>> Amateur Callsign: WB4UIV wb4uiv at arrl.net AMSAT LM 2178
>>> QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
>>> "It is not the class of license that the Amateur holds but the class
>>> of the Amateur that holds the license"
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