[time-nuts] Antique precision timing device without

Bob Camp kb8tq at n1k.org
Sat Mar 18 09:39:19 EDT 2017


> On Mar 17, 2017, at 7:41 PM, Morris Odell <vilgotch at bigpond.net.au> wrote:
> HI all,
> Thanks to all those who responded to my post and also for the great pics of
> other tuning forks. It's amazing that they were still being used for
> electronic purposes as recently as the 1960s.

Motorola was still very much in the business of making Vibrasenders and Vibrasponders
to generate and decode PL tones on FM radios well into the 1980’s. They were 
really not much more than tuning forks set to the proper tone frequency.


> Actually now that I think
> about it I have seen little tuning forks used to check the function of
> modern police speed radars so they still have some use. Musicians don't use
> them any more - guitar players will know the little electronic tuning
> devices clipped to the  neck of the instrument that displays the frequency
> or key of each string. Doctors still use 125 Hz forks to test vibration
> sense and higher frequency ones to test for conductive hearing loss. 
> In answer to some of the questions posted: no there was no documentation
> with the unit. The most useful thing was the "12 volts in" label on the
> power socket so I knew where to start. The rest of it was necktop analysis.
> The fork is maintained by means of a central electromagnet and small leaf
> spring contacts on the tines - they also provide the 25 Hz power for the
> motor which runs at 12 volts. Of course they would reduce the Q of the fork
> a little and affect its resonance but I'm sure that was taken into  account
> by the designer and the frequency & symmetry can be adjusted with the
> weights on the ends. Operating current is about 0.5A at 12 volts when
> running and 1A when the fork is not vibrating. There's a switch marked "Neon
> Lamp" that controls the AC supply to a pair of clips between the tines of
> the fork. They are about 3-4 inches apart and I have no idea what sort of
> long thin tubular lamp would fit between them. Just for fun I'm going to
> make a simple stroboscope with a 555 timer and some high intensity white
> LEDs I have lying around to see if I can use it on the fork.
> Cheers,
> Morris
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