[time-nuts] General Radio Model 723D Precision Oscillator (Tuning Fork)

[paul swed]

Here is the link to some fine pictures and the schematic. Its uasable.
http://worldpowersystems.com/J/instruments/GR723/
As a heads up the AC power comes in and is immediately doubled.
Loaded something like 164 VDC.
Reg tubes 107 V.
Osc draws 35 Ma at 135V B+.
Fil 1.42V at 47 ma.
Distortions quite low .219% Tek AA501.
IMD 5.59% Tek AA501.
I actually used independent supplies when I fired it up the first time.
Totally did not trust the power supply.
Takes about 20 seconds to start up.
You will hear it running quite apparent.
I have a theory. Crystals were invented so you would not need to listen to
the tuning fork.
Regards
Paul
WB8TSL



On Sat, Dec 9, 2017 at 11:37 AM, paul swed <paulswedb at gmail.com> wrote:

> Well we are kicking butt on 723 oscillators. I have the 1000 hz model and
> found it at the MIT flea about June.
> Bad rectifier section. Cap was good though I carefully reformed it. Have
> to say what attracted me was the case and then the realization of what it
> was. It works very well so now I can make sure my cesium is on frequency.
> There is a schematic online but its a picture actually in the wood case. I
> copied that as I could find no real details.
> I do have the genrad article.
> The actual internals are hot. Be careful. It uses an output transformer as
> the only isolation.
> It makes sense actually. It keeps the 60 Hz magnetics out of the
> oscillator.
> I thought my tube might be bad as it didn't glow. But its a 1.5 V filament
> ohm'ed it out and it was fine.
> Lastly I have a hacked power cable. I was going to buy the right plug. But
> it actually is a bit unclear. It should be the cenetr ground and they are
> around $15 each. Its not the cost. The 3 I see are sort of unclear that
> they match my socket.
> I swear I actually have one. Some place here.
> Regards
> Paul
> WB8TSL
>
> On Sat, Dec 9, 2017 at 10:30 AM, Eric Scace <eric at scace.org> wrote:
>
>> Another fascinating tuning-fork standard was used together with a
>> Synchronome to govern the timing of pulses of Morse code on undersea
>> telegraph cables in the British empire’s globe-girdling telegraph network.
>> Timing was derived electromagnetically from incoming Morse code signals (a
>> bi-polar signal where one polarity represented a dit and the other a dah,
>> but both dit and dah were of equal length) to set the master at each
>> downstream relay/switching station on a cable route.
>>
>> In essence, brass, mahogany and electromagnetics were use to perform all
>> the functions done today on fiber optic cables: signal generation,
>> multiplexing, regeneration, and timing recovery… not to mention encoding &
>> decoding plus printing.
>>
>> One can see a working example at the Museum of Undersea Telegraphy in
>> Porth Curno, Cornwall — a museum well worth the detour to Land’s End.
>>
>> — Eric
>>
>> > On 2017 Dec 09, at 10:11 , Don <dlewis6767 at austin.rr.com> wrote:
>> >
>> > Thank you, Pete.   -Don
>> >
>> > ==========================
>> >
>> >
>> >
>> >
>> > On Sat, 2017-12-09 at 05:57 -0800, Pete Lancashire wrote:
>> >> Here's a look at a 723-C (1,000 cps) and how its power supply cap was
>> >> handled and a good look inside
>> >>
>> >> https://www.eevblog.com/forum/reviews/vintage-teardown-general-radio-
>> >> 723-c-vacuum-tube-tuning-fork/
>> >>
>> >>
>> >> The GR Experimenter
>> >>
>> >> http://www.americanradiohistory.com/Archive-General-Radio/GR%20Exp%20
>> >> 1941_10.pdf
>> >>
>> >> There is another Experimenter that goes into how the tuningfork was
>> >> made
>> >> but can't find it
>> >>
>> >> -pete
>> >>
>> >> On Sat, Dec 9, 2017 at 5:18 AM, Don <dlewis6767 at austin.rr.com> wrote:
>> >>
>> >>>
>> >>>>
>> >>>> I was fortunate to find a vintage, General Radio (GR) Model 723D
>> >>>> Precision Oscillator (tuning fork).
>> >>>>
>> >>>> The exceptional wooden case is as 'exciting' to look at as is the
>> >>>> mechanical tuning fork inside (400Hz).
>> >>>>
>> >>>> As it is ac powered, I'll need to recap it before I turn it on.
>> >>>>  Then, we can test for accuracy! (sic).
>> >>>>
>> >>>> A real class-act, 'time-nut' oscillator from the last century,
>> >>>> predating crystals.
>> >>>>
>> >>>> Don
>> >>>>
>> >>>> Don Lewis
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>
>