[time-nuts] Antique precision timing device without electronics

Mike Seguin n1jez at burlingtontelecom.net
Thu Mar 16 17:33:12 EDT 2017

Very interesting use of a tuning fork.

I have only seen this once before. I have the tuning fork used with an 
Ampex Model 300 reel to reel tape machine. The tuning fork was used as a 
reference in the power supply that drove the capstan motor for accurate 

It's 60 Hz not 25 Hz. It's marked B E Eisenhour. Patent is here:


Pic is here:



On 3/16/2017 2:04 PM, Bill Hawkins wrote:
> Hi Morris,
> If there's no active devices (and you'd be sure to see them, not solid
> state) where does the power to operate the motor come from? Is it the
> same contacts that drive the fork?
> It's amazing that there is high Q when contacts must be operated by the
> fork.
> Did it come with instructions for setting the weights at the end of the
> fork tines?
> Best regards,
> Bill Hawkins
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Morris
> Odell
> Sent: Thursday, March 16, 2017 4:23 AM
> To: time-nuts at febo.com
> Subject: [time-nuts] Antique precision timing device without electronics
> Hi all,
> I was recently asked to resurrect this interesting device by a colleague
> who collects antique scientific instruments. It's a "Chronoscope" made
> by the H. Tinsley company in London in the early 20th century and used
> to measure time intervals with the precision of those days. It's large
> and heavy in a polished wooden case with a top deck that hinges up to
> reveal the innards.
> The timing reference is a large tuning fork about 30 cm (1 foot) long
> and running at 25 cps. It's normally in a glass fronted housing (removed
> for the video) that includes a pair of hinged mechanical arms for
> starting it. It's maintained in oscillation by an electromagnet and
> contact arrangement powered from a 12V DC supply. The fork amplitude is
> controlled by a rheostat - too much and the tines impact on the magnet.
> The video frame rate makes the fork look slower than it actually is. I
> was able to extract a signal and measure the frequency with a modern GPS
> disciplined counter - it's 0.007% off its specified 25 Hz! The frequency
> is too low for my HP 5372A so I was not able to easily get an idea of
> stability or do an ADEV measurement. The fork has quite a high Q and
> takes over a minute to stop oscillating after the power is turned off.
> There's a built in higher voltage AC power supply, probably a mains
> transformer, potted in beeswax in a polished wooden box inside that is
> intended to
>   energise a large neon strobe lamp used to adjust the fork.
> Unfortunately the lamp was not with the unit and is no doubt
> irreplaceable.
> The 25 Hz signal is filtered by an LC network  and used to run a
> synchronous motor in the Chronoscope unit. Synchronous motors not being
> self-starting, you need to tweak a knob to get it going - there's a joke
> in there but I can't for the life of me think what it could be ?? The
> "Contact" switch and associated socket on the back controls an
> electromagnetic clutch that connects the clockwork counter mechanism to
> the motor and the contact "on" time is indicated on the dials with 10 mS
> resolution.
> There's not a single active device in there and after a clean and lube
> it runs very nicely from a modern 12V DC plugpack. My friend is very
> pleased with it and it will take pride of place in his collection.
> I'd be interested to know if any time nuts have knowledge or experience
> of this lovely instrument.
> A video of it is at  https://youtu.be/i5S8WS9iN_E
> Enjoy!
> Morris
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.


Mike, N1JEZ
"A closed mouth gathers no feet"

More information about the time-nuts mailing list