Re: [time-nuts] Helmholtz Resonator and other Maintained Oscillators

[Ulrich Rohde via time-nuts]

 
This is a very nice technical discussion ...
 
Ulrich
 
 
In a message dated 12/9/2017 7:31:15 PM Eastern Standard Time, 
t...@radio.sent.com writes:

 
 The Q of Helmholtz resonators is derived here:
https://en.wikibooks.org/wiki/Acoustics/Flow-induced_Oscillations_of_a_Helmholtz_Resonator

Some Q measurements of bottles are described here:
https://math.dartmouth.edu/archive/m5f10/public_html/proj/ArainGolvach.pdf

--
Bill Byrom N5BB

On Sat, Dec 9, 2017, at 01:39 AM, Hal Murray wrote:
> 
> k8yumdoo...@gmail.com said:
> > The flex hose demonstration was interesting in that different regimes of
> > swinging speed resulted in oscillation in different modes. I wonder why.
> 
> It depends on the speed of the air going through the tube.
> 
> https://www.youtube.com/watch?v=4aJ36-TlPD4
> 
> http://www.exo.net/~pauld/activities/AAAS/aaas2001.html
> http://www.exo.net/~pauld/summer_institute/summer_day13music/Whirly.html
> 
> 
> -- 
> These are my opinions. I hate spam.
> 
> 
> 
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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Tom Holmes]

Mark...
You're place really moved a foot in 48 hours? Impressive and scary!

>From Tom Holmes, N8ZM

> On Dec 9, 2017, at 8:19 PM, Mark Sims  wrote:
> 
> Which gets real fun with things like solid earth tides getting involved.   
> Lady Heather can now calculate and plot solid earth tides.   Over the last 48 
> hours my place moved up/down 315 mm and gravity changed 186  microgals... and 
> that was a rather stable period.
> 
> --
> 
>> A 1 meter change in elevation corresponds to a frequency offset of about 
>> 1e-16. So for 1e-18 levels of performance you "only" need to know g, or your 
>> elevation to 1 cm accuracy.
> 
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[time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Mark Sims]

Which gets real fun with things like solid earth tides getting involved.   Lady 
Heather can now calculate and plot solid earth tides.   Over the last 48 hours 
my place moved up/down 315 mm and gravity changed 186  microgals... and that 
was a rather stable period.

--

> A 1 meter change in elevation corresponds to a frequency offset of about 
> 1e-16. So for 1e-18 levels of performance you "only" need to know g, or your 
> elevation to 1 cm accuracy.___
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[time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Mark Sims]

Yep, to paraphrase Bunker Hunt's "a billion dollars ain't what it used to 
be"... a nanosecond (or picosecond) ain't what it used to be.  Things that used 
to be insignificant n'th order theoretical nuisances are now very real 
significant problems.



> But it's not one-to-one as you suggest. A 1 meter change in elevation 
> corresponds to a frequency offset of about 1e-16. So for 1e-18 levels of 
> performance you "only" need to know g, or your elevation to 1 cm accuracy.
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Re: [time-nuts] Helmholtz Resonator and other Maintained Oscillators

[Bill Byrom]

The Q of Helmholtz resonators is derived here:
https://en.wikibooks.org/wiki/Acoustics/Flow-induced_Oscillations_of_a_Helmholtz_Resonator

Some Q measurements of bottles are described here:
https://math.dartmouth.edu/archive/m5f10/public_html/proj/ArainGolvach.pdf

--
Bill Byrom N5BB

On Sat, Dec 9, 2017, at 01:39 AM, Hal Murray wrote:
> 
> k8yumdoo...@gmail.com said:
> > The flex hose demonstration was interesting in that different regimes of
> > swinging speed resulted in oscillation in different modes.  I wonder why.
> 
> It depends on the speed of the air going through the tube.
> 
> https://www.youtube.com/watch?v=4aJ36-TlPD4
> 
> http://www.exo.net/~pauld/activities/AAAS/aaas2001.html
> http://www.exo.net/~pauld/summer_institute/summer_day13music/Whirly.html
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> ___
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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Tom Van Baak]

Mark,

> In the standards definitions that include "at sea level", the question these 
> days is "which sea level?".

Chris,

> So does that mean e.g. NIST and BIPM need to measure the acceleration at
> their respective locations to within parts in 10^17 or 10^18 in order to
> compare their frequency standards?

Yes, all national timing labs do this to one degree or another. To operate and 
compare clocks at that level of precision you need to accurately know your 
geopotential, which is sort of like knowing the acceleration of gravity, or 
elevation.

But it's not one-to-one as you suggest. A 1 meter change in elevation 
corresponds to a frequency offset of about 1e-16. So for 1e-18 levels of 
performance you "only" need to know g, or your elevation to 1 cm accuracy.

> That seems not practical.

It is practical, and necessary, and really cool!

Here are some papers that will give you an idea how much work it takes to make 
clocks at the 1e-16 and 1e-17 level. I mean, it's not like you just throw some 
cesium atoms in a bottle, rub the lamp, and out comes a genie singing 
9192.631770 MHz.

These two examples describe the complexity of a primary cesium standard:

"Accuracy evaluation of the primary frequency standard NIST-7", 2001
http://tf.nist.gov/timefreq/general/pdf/1497.pdf

"Accuracy evaluation of NIST-F1", 2002
http://tf.nist.gov/timefreq/general/pdf/1823.pdf

In the first paper, see especially tables 1, 3 and 4 for an idea of the 
corrections they must apply. You'll notice that the largest correction is 
gravitational. Therefore part of their job in making a primary standard is to 
measure gravity at the exact point where the cesium atoms operate. And yes, 
that gets you in the dirty world of what's underground, what mountains are 
nearby, where's the water table this week, what shape the earth really is, and 
the phase of the moon, etc.

These two examples describe the complexity of precisely measuring gravity in 
order to calibrate an atomic clock:

"The relativistic redshift with 3 × 10−17 uncertainty at NIST, Boulder, 
Colorado, USA", 2003
http://tf.boulder.nist.gov/general/pdf/1846.pdf

"A re-evaluation of the relativistic redshift on frequency standards at NIST, 
Boulder, Colorado, USA", 2017
http://tf.boulder.nist.gov/general/pdf/2883.pdf

Really, all four papers are worth a quick read, even if you just look at the 
tables and photos.

/tvb

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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Bob kb8tq]

Hi

If the frequency sensitivity is 1x10^-13 / G you don’t need a lot of precision
in your measurement of G. The same issues apply to things like magnetic 
field and the rest. 

Bob

> On Dec 9, 2017, at 4:02 PM, Chris Caudle  wrote:
> 
> On Sat, December 9, 2017 2:39 pm, Magnus Danielson wrote:
>> The standard acceleration is internationally agreed at 3rd CGPM in 1901
>> to be 9.80665 m/s^2.
> 
> So does that mean e.g. NIST and BIPM need to measure the acceleration at
> their respective locations to within parts in 10^17 or 10^18 in order to
> compare their frequency standards?
> That seems not practical.
> -- 
> Chris Caudle
> 
> 
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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Magnus Danielson]

Hi,

On 12/09/2017 10:02 PM, Chris Caudle wrote:

On Sat, December 9, 2017 2:39 pm, Magnus Danielson wrote:

The standard acceleration is internationally agreed at 3rd CGPM in 1901
to be 9.80665 m/s^2.


So does that mean e.g. NIST and BIPM need to measure the acceleration at
their respective locations to within parts in 10^17 or 10^18 in order to
compare their frequency standards?
That seems not practical.


No, you have a large scale-factor so you really don't need that much of 
precision to achieve it.


Cheers,
Magnus
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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Chris Caudle]

On Sat, December 9, 2017 2:39 pm, Magnus Danielson wrote:
> The standard acceleration is internationally agreed at 3rd CGPM in 1901
> to be 9.80665 m/s^2.

So does that mean e.g. NIST and BIPM need to measure the acceleration at
their respective locations to within parts in 10^17 or 10^18 in order to
compare their frequency standards?
That seems not practical.
-- 
Chris Caudle


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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Magnus Danielson]

Hi,

On 12/09/2017 09:13 PM, Bob kb8tq wrote:

Hi

I suspect that at the practical level, you define standard atmospheric 
pressure, standard
gravity, standard magnetic field ….. and on down the list. At some point “sea 
level” becomes
a redundant expression.


The standard acceleration is internationally agreed at 3rd CGPM in 1901 
to be 9.80665 m/s^2. So, that is "sea level". See SI brochure, I used 
version 8 in english, page 143.


This is also the standard value I have in my calculators and used for 
all my acceleration calculations.


In practice labs have their contributions into EAL/TAI corrected for 
their deviation from "sea level" for proper frequency of TAI.


Cheers,
Magnus


Bob


On Dec 9, 2017, at 2:14 PM, Mark Sims  wrote:

In the standards definitions that include "at sea level", the question these days is "which 
sea level?".  As ocean temperature changes sea level will change (except maybe in Washington DC).  Will 
the standards be amended to include something like "at sea level in 1990" or will the value being 
defined drift around with the changing sea level?
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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Bob kb8tq]

Hi

I suspect that at the practical level, you define standard atmospheric 
pressure, standard 
gravity, standard magnetic field ….. and on down the list. At some point “sea 
level” becomes
a redundant expression.

Bob

> On Dec 9, 2017, at 2:14 PM, Mark Sims  wrote:
> 
> In the standards definitions that include "at sea level", the question these 
> days is "which sea level?".  As ocean temperature changes sea level will 
> change (except maybe in Washington DC).  Will the standards be amended to 
> include something like "at sea level in 1990" or will the value being defined 
> drift around with the changing sea level?
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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[jimlux]

On 12/9/17 11:14 AM, Mark Sims wrote:

In the standards definitions that include "at sea level", the question these days is "which 
sea level?".  As ocean temperature changes sea level will change (except maybe in Washington DC).  Will 
the standards be amended to include something like "at sea level in 1990" or will the value being 
defined drift around with the changing sea level?


Sea Level is arbitrary anyway - what is usually meant is "zero elevation 
relative to some specified geoid".


 The Pacific and Atlantic oceans have different mean heights relative 
to the geoid


In the United States, for a long time it was the North American Datum 
(NAD) that was the reference, but now, it's probably WGS84 (I'm too lazy 
to go look it up).


WGS84 has a very precise definition in terms of the semiaxes lengths, 
and their orientation relative to stellar references.  WGS 84 uses the 
IERS reference meridian for longitude.


Flattening of 1/298.257,223,563
equatorial radius of 6,378,137 m
so polar radius of 6,356,752.3142 m

The Earth Grav Model (EGM96) defines the geoid, last revised in 2004. 
*that* model defines the nominal sea surface with spherical harmonics. 
There's something like 100,000 specific terms in that gravity model.


Sourceforge has a program that will tell you geoid height for a given 
lat lon.


https://geographiclib.sourceforge.io/cgi-bin/GeoidEval

Near my house (34N, 119W), it appears that the EGM96 height is -37.17 m, 
relative to the ellipsoid defined above.


It so happens that due to crustal movement, my house is gradually rising 
about 1 cm/year, but I don't know if the local sea level also rises to 
match, or if the beach is getting farther away.



One can measure this, in theory
https://www.unavco.org/education/resources/modules-and-activities/gps-california-plate-motion/gps-california-plate-motion.html










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[time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Mark Sims]

In the standards definitions that include "at sea level", the question these 
days is "which sea level?".  As ocean temperature changes sea level will change 
(except maybe in Washington DC).  Will the standards be amended to include 
something like "at sea level in 1990" or will the value being defined drift 
around with the changing sea level?
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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Bob kb8tq]

Hi

If you dig back into the various papers on the subject (and the proceedings
that log the post paper questions) the issue of “can we trust the 
implementation?”
does indeed come up. It’s come up for at least the last 50 years that I’m aware 
of.
The basic argument runs that for fundamental standards, you need to approach
the process in different ways. You then compare the results from those 
different 
methods. Only after you have done that, do you build confidence in the accuracy
of the various processes. Indeed once you have built confidence in a single 
approach, 
you may decide to all go with that one approach or implementation. 

Bob

> On Dec 9, 2017, at 12:54 PM, Chris Caudle  wrote:
> 
> There is a piece missing for me in the articles I have found on new atomic
> standards.
> 
> This is what I (think I) do understand:
> Quantum properties of the atoms can be interrogated using various RF or
> optical means to servo the frequency of an oscillator (which could be a
> laser based optical  oscillator).
> 
> The international standard for frequency (based on time) is defined in
> terms of a theoretical condition of cesium atoms which cannot be perfectly
> achieved in practice, needing absolute zero temperature,
> gravity/acceleration equivalent exactly to mean sea level of earth, no
> magnetic perturbation, no interaction such as bouncing off of cavity
> walls, etc.
> 
> New optical standards can achieve "accuracies" of parts in 10^16, verified
> by comparing multiple instances of the standards with each other, and if
> the standards are built correctly and the theory of operation is correct,
> the multiple separate pieces of equipment should agree in frequency output
> to within some parts in 10^x, where x has historically been around 15, but
> is now reaching toward 17.
> 
> So far so good, but here is where I have a gap:
> I put "accuracies" in quotations above because as far as I understand you
> can actually compare consistency of center frequency or stability over
> periods of time between two instances of a particular type of atomic
> oscillator, but accuracy in the sense of comparing how closely the the
> output frequency matches the calculated theoretical output frequency
> (assuming that the operating mechanism is fully understood) is going to
> depend on having a reference for comparison that is as good or better than
> the new standard to be measured.  That implies that the reference has
> systematic offset that is known to better than parts in 10^17, but that
> would require knowing the quantum properties of the atoms in use to that
> level, knowing the gravitational potential at your location to that level,
> knowing that the temperature dependence of the equipment was below that
> level, etc.
> 
> How can anyone ever talk about accuracy in the terms of SI second
> definition for these new oscillators?  Are they really using layman's
> shorthand, and they mean stability and consistency?  Or are they really
> able to measure all the other factors well enough that they can actually
> mean accuracy in the sense of how the SI second definition calls out
> absolute zero, gravitational potential, etc.?
> 
> -- 
> Chris Caudle
> 
> 
> 
> 
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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Bob Albert via time-nuts]

 So we leave the scientific considerations and delve into the philosophical 
basis.  Somewhere down the line, a standard has to be established, to which all 
others can be compared.  How good this standard is doesn't matter, as long as 
it's stable.  But how does one measure stability?  Against what?
The fundamental standard is, I think, the revolution of the earth about the 
sun.  Even that is subject to significant perturbations.  If one takes, 
instead, the resonant frequency of a vibrating atom, as you say it is subject 
to some variation due to its environment.
So this elusive number will always remain elusive because of its very nature.  
Yes, one can  refine the measurements, but still some uncertainty will remain.  
And who was the one who said that all cesium atoms are the same?  I suspect 
each atom is unique, that its mass and charge and natural frequency and so on 
are different for every atom, even though very close.
One could then talk about an average of all cesium atoms but statistically that 
will only narrow the uncertainty about one order of magnitude.
So the answer to your question is, I believe, that there is no answer to your 
question.  Like slaves we are bound to refine our measurements even though we 
know we can never reach the absolute.
I ponder a moment and think, well it's probably about 10 o'clock.  I look at 
the clock and find that I am a few minutes off.  I think that's close enough 
for most of my life.  I bought a watch that is about a second a day in error so 
I find myself resetting it often.  I am the only one who cares.
Just a few thoughts in passing.  Go to the group called Volt Nuts and they go 
through similar agonies.
Bob
On Saturday, December 9, 2017, 9:55:00 AM PST, Chris Caudle 
 wrote:  
 
 There is a piece missing for me in the articles I have found on new atomic
standards.

This is what I (think I) do understand:
Quantum properties of the atoms can be interrogated using various RF or
optical means to servo the frequency of an oscillator (which could be a
laser based optical  oscillator).

The international standard for frequency (based on time) is defined in
terms of a theoretical condition of cesium atoms which cannot be perfectly
achieved in practice, needing absolute zero temperature,
gravity/acceleration equivalent exactly to mean sea level of earth, no
magnetic perturbation, no interaction such as bouncing off of cavity
walls, etc.

New optical standards can achieve "accuracies" of parts in 10^16, verified
by comparing multiple instances of the standards with each other, and if
the standards are built correctly and the theory of operation is correct,
the multiple separate pieces of equipment should agree in frequency output
to within some parts in 10^x, where x has historically been around 15, but
is now reaching toward 17.

So far so good, but here is where I have a gap:
I put "accuracies" in quotations above because as far as I understand you
can actually compare consistency of center frequency or stability over
periods of time between two instances of a particular type of atomic
oscillator, but accuracy in the sense of comparing how closely the the
output frequency matches the calculated theoretical output frequency
(assuming that the operating mechanism is fully understood) is going to
depend on having a reference for comparison that is as good or better than
the new standard to be measured.  That implies that the reference has
systematic offset that is known to better than parts in 10^17, but that
would require knowing the quantum properties of the atoms in use to that
level, knowing the gravitational potential at your location to that level,
knowing that the temperature dependence of the equipment was below that
level, etc.

How can anyone ever talk about accuracy in the terms of SI second
definition for these new oscillators?  Are they really using layman's
shorthand, and they mean stability and consistency?  Or are they really
able to measure all the other factors well enough that they can actually
mean accuracy in the sense of how the SI second definition calls out
absolute zero, gravitational potential, etc.?

-- 
Chris Caudle




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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference

[Chris Caudle]

There is a piece missing for me in the articles I have found on new atomic
standards.

This is what I (think I) do understand:
Quantum properties of the atoms can be interrogated using various RF or
optical means to servo the frequency of an oscillator (which could be a
laser based optical  oscillator).

The international standard for frequency (based on time) is defined in
terms of a theoretical condition of cesium atoms which cannot be perfectly
achieved in practice, needing absolute zero temperature,
gravity/acceleration equivalent exactly to mean sea level of earth, no
magnetic perturbation, no interaction such as bouncing off of cavity
walls, etc.

New optical standards can achieve "accuracies" of parts in 10^16, verified
by comparing multiple instances of the standards with each other, and if
the standards are built correctly and the theory of operation is correct,
the multiple separate pieces of equipment should agree in frequency output
to within some parts in 10^x, where x has historically been around 15, but
is now reaching toward 17.

So far so good, but here is where I have a gap:
I put "accuracies" in quotations above because as far as I understand you
can actually compare consistency of center frequency or stability over
periods of time between two instances of a particular type of atomic
oscillator, but accuracy in the sense of comparing how closely the the
output frequency matches the calculated theoretical output frequency
(assuming that the operating mechanism is fully understood) is going to
depend on having a reference for comparison that is as good or better than
the new standard to be measured.  That implies that the reference has
systematic offset that is known to better than parts in 10^17, but that
would require knowing the quantum properties of the atoms in use to that
level, knowing the gravitational potential at your location to that level,
knowing that the temperature dependence of the equipment was below that
level, etc.

How can anyone ever talk about accuracy in the terms of SI second
definition for these new oscillators?  Are they really using layman's
shorthand, and they mean stability and consistency?  Or are they really
able to measure all the other factors well enough that they can actually
mean accuracy in the sense of how the SI second definition calls out
absolute zero, gravitational potential, etc.?

-- 
Chris Caudle




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

[paul swed]

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  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  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  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
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
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>
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Re: [time-nuts] General Radio Model 723D Precision Oscillator (Tuning Fork)

[Eric Scace]

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

[Don]

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  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
> > > Austin, TX
> > > N5CID
> > > 
> > > 
> > > 
> > > 
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to https://www.febo.com/cgi-bin/
> > mailman/listinfo/time-nuts
> > and follow the instructions there.
> > 
> ___
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> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/t
> ime-nuts
> and follow the instructions there.
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Re: [time-nuts] General Radio Model 723D Precision Oscillator (Tuning Fork)

[Pete Lancashire]

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%201941_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  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
> > Austin, TX
> > N5CID
> >
> >
> >
> >
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>
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[time-nuts] General Radio Model 723D Precision Oscillator (Tuning Fork)

[Don]

> 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
> Austin, TX
> N5CID
> 
> 
> 
> 
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