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Old 16th May 2022, 10:53 am   #1
pcravero
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Default The James Knights Co. oscillator, 4.0 kc

Hello.
Last Saturday at the most pleasant open-air radio-electronics-only flea market held in Marzaglia (near Modena, Italy) I picked a circuit with a strange component.

It is a tall metallic cylinder probably made in 1957 by The James Knights Co. Other labels say "avg temperature 57C" and "thermostat 6.3V". I think it is an ovenised oscillator at 4.0 kc/kHz, but at the supposedly output pin I don't read a signal.

The circuitry in the box is composed of a 7805 regulator and a transistor buffer on the output. If I power it up the tube heats up to <40 C. I see a difference in current input in a cycle on-off of about 8 seconds per state.

Four wires go to the socket: AC heater, GND, +5Vdc and a sort of 50 Hz drive signal. And one (silent) output.

The oscillator may be broken, so I'll keep it as a novelty item or a hand warmer. But I wonder which application could have used an OC(X)O at 4.0 kHz. If I can get my eyes on a circuit diagram using a similar component I might find out if it has been (re)wired incorrectly.

Thank you,
Paolo

PS: Marzaglia is held the 2nd Saturday of May and September. May is typically more crowded if you want to plan a trip (https://www.marzaglia.it/).
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Old 16th May 2022, 1:14 pm   #2
Jon_G4MDC
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Default Re: The James Knights Co. oscillator, 4.0 kc

Might that be an ovenised 4kHz resonator not a whole oscillator?
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Old 16th May 2022, 7:31 pm   #3
barrymagrec
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Default Re: The James Knights Co. oscillator, 4.0 kc

If it`s 1957 the7805 may not be an original component.....
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Old 16th May 2022, 8:34 pm   #4
Nickthedentist
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Default Re: The James Knights Co. oscillator, 4.0 kc

Yes, the thing in the golden tube may well date from 1957 but the periperhal components in the green box look 1980s onwards and distinctly homebrew
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Old 17th May 2022, 1:12 pm   #5
pcravero
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Default Re: The James Knights Co. oscillator, 4.0 kc

Yes, it's indeed homebrew and it uses components that span some decades. By the way, I've never met a 7805 in that case (see pics).

I reversed the circuit around the transistor and it looks like an oscillator where the big tube is the resonator element, so Jon is right. Looking through the top hole with a strong light I see a small trimcap. Let's see if I can open the can without damages.

Paolo
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Old 17th May 2022, 1:35 pm   #6
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Default Re: The James Knights Co. oscillator, 4.0 kc

Interesting.

The only thing I can think it might have been part of is some kind of Audio multiplex.
One channel is at baseband, say 300Hz - 3.5kHz and the other channel is mixed up to 4.3 - 7.5kHz.

Pye used to call theirs a 1+1.

(PS I have had a 7805 in that package before)
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Old 17th May 2022, 9:42 pm   #7
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Default Re: The James Knights Co. oscillator, 4.0 kc

THe resonator could be any of a number of things.... A flexural-shear mode quartz bar, probably in an evacuated glass holder, maybe a quartz tuning fork in vacuo. or a metal tuning fork also in vacuo. Any of these would benefit from an ovened environment.

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Old 20th May 2022, 7:33 am   #8
pcravero
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Default Re: The James Knights Co. oscillator, 4.0 kc

I had to see the resonator and I found a surprise. A previous owner has replaced the original innards with a 10'000 kc/s XTAL oscillator, so he got an ovenised XO. Well, I might try crystal grinding to put it on 30m HAM band. I did measure once a 10 MHz output, but discarded it as noise and never appeared again in later tests, probably due to loose contacts inside the tube.

The curiosity remains on which device used a 4 kc OXO in 1957.

Thanks for reading and contributing!
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