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Old 25th Feb 2020, 2:45 am   #1
radiograham
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Default Professor Theremin advert.

I was wondering if anybody had noticed this ad on dave which features at the end a musical oscillator which is played by hand movement and a horn speaker of some sort,no doubt a mock up of professor theremin and his oscillating "music box as featured in popular wireless dec 31st 1927.
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Old 25th Feb 2020, 3:27 am   #2
dave walsh
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Default Re: Professor Theremin advert.

Yes I've seen that Graham. I was ill in the mid nineties and couldn't make a concert in Southampton when his Granddaughter played the Theremin in Concert. The BBC recorded it and the manager of the venue sent me a tape copy. You wouldn't get that now. CH4 did a great Documentary about him.

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Old 25th Feb 2020, 10:48 am   #3
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Default Re: Professor Theremin advert.

Nice Video of Theramin here.

https://www.youtube.com/watch?v=w5qf9O6c20o

Cheers

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Old 25th Feb 2020, 12:02 pm   #4
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Default Re: Professor Theremin advert.

The Theremin musical instrument was a superb idea, but his bug in the American embassy was pure genius.

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Old 25th Feb 2020, 12:15 pm   #5
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Default Re: Professor Theremin advert.

It's said that Theremin was tasked with developing an electronic mine detector in the aftermath of the civil war in Russia and his eponymous instrument was a spin-off from this work. As so often, it's difficult to pin the facts down, but it would seem credible.
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Old 25th Feb 2020, 7:45 pm   #6
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Default Re: Professor Theremin advert.

I sold my theremin, I hadn't touched it in years
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Old 25th Feb 2020, 11:52 pm   #7
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Default Re: Professor Theremin advert.

The documentary can be found on DVD. It's called 'Theremin - an electronic odyssey'.

I found it incredibly moving. It features luminaries such as Bob Moog.

An amazing innovator. Well worth watching.
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Old 26th Feb 2020, 12:58 am   #8
radiograham
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Default Re: Professor Theremin advert.

Hi ,I didn't know he was that well known until I read up on him, always thought it was a novelty from the 1920's, I know better now.As regards the advert is that a genuine instrument he is playing or a mock up?

Graham.
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Old 26th Feb 2020, 1:59 am   #9
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Default Re: Professor Theremin advert.

A Theremin even found its way into a Clangers episode a few months ago - there's an excerpt at https://www.youtube.com/watch?v=PK72k3q6SrU and I'm sure that you'll be able to see the full episode in a few weeks time when they repeat it.
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Old 26th Feb 2020, 10:18 am   #10
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Default Re: Professor Theremin advert.

The Theremin in the advert is a Moog Etherwave Pro.
These were a limited edition and are highly thought of (and expensive!).
The 'performer' IMHO is miming to the sound you can hear.

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Old 26th Feb 2020, 11:05 am   #11
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Default Re: Professor Theremin advert.

Does anyone know if Theremin's original circuit is in the open? There are any number of "Theremin-alike" circuits on the 'net involving valves, BJTs. FETs, ICs, but I believe (this is sketchy!) that the original used a saturable reactor to control the filament current of a valve amplifying/buffering the heterodyne product and hence output level. Considering this mechanism, not to mention the available technology of the early '20s, I think this would need to have been a bright emitter type?
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Old 26th Feb 2020, 11:22 am   #12
TonyDuell
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Default Re: Professor Theremin advert.

I found the service manual for the RCA Theremin on some site or other. I am not sure if its the same circuit, but the volume control RF oscillator powers the filament of one of the valves directly, controlling the fillament current controls the volume.

If you think it would be useful, and can't find it, PM me with your e-mail address and I'll send it to you.
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Old 26th Feb 2020, 11:55 am   #13
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Default Re: Professor Theremin advert.

There are some circuit details of the RCA theremin plus others on Art Harrison's website :- https://www.theremin.us/
Plus some detailed info here :- http://www.thereminworld.com/RCA-Theremin-Tech

HTH
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Last edited by radioman; 26th Feb 2020 at 12:04 pm. Reason: Additional info.
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Old 26th Feb 2020, 5:31 pm   #14
Jon_G4MDC
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Default Re: Professor Theremin advert.

I was suspicious of that volume modulator in the RCA circuit. I wondered if they had somehow wrongly drawn the filament connections, thinking too much power would be needed. I was suspecting the valve would be heated by other means and the Volume Oscillator was only changing the bias by g-k rectification.

Looking again, and that the UX120 was a 3.3V Valve for battery portables maybe it was powering the heater after all.

Hand capacitance to the volume antenna would increase primary current in the transformer meaning output at the secondary and that would heat up the valve.
Thermal lag must have limited how fast the Volume would swell.

Did you need a radio licence to run one of these?

Last edited by Jon_G4MDC; 26th Feb 2020 at 5:40 pm.
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Old 26th Feb 2020, 8:20 pm   #15
David G4EBT
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Default Re: Professor Theremin advert.

I dare say it's much harder than it looks to play a theramin in any meaningful way beyond making 'other worldly' spooky sounds.

This is a very impressive demonstration of a theramin being expertly played in a cover version of the Gnarles Barclay's song 'Crazy'.

https://www.youtube.com/watch?v=mW0B1sipLBI

Here's the Gnarles Barclay original:

https://www.youtube.com/watch?v=mW0B1sipLBI
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Old 26th Feb 2020, 9:01 pm   #16
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Default Re: Professor Theremin advert.

And an original Moog Theremin is used by Jean Michel Jarre, being seen in the Oxygene: Live In Your Living Room, and Oxygene In Moscow.
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Old 26th Feb 2020, 9:52 pm   #17
turretslug
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Default Re: Professor Theremin advert.

Quote:
Originally Posted by TonyDuell View Post
I found the service manual for the RCA Theremin on some site or other. I am not sure if its the same circuit, but the volume control RF oscillator powers the filament of one of the valves directly, controlling the fillament current controls the volume.

If you think it would be useful, and can't find it, PM me with your e-mail address and I'll send it to you.
Thanks for the offer, it was more curiosity, really- sad I know, but I'd long wondered how proximity control of filament current was achieved in the early 1920s. I did find a circuit involving 6C4s and a 6BE6, etc., i.e. late '40s/early '50s era, for electronic gain control- I know common sense says that semiconductors are the way to go, but the mystique of the instrument suggests that thermionics would add to the aura. Using polyester resin and fibreglass matting on a Stradivarius would probably work perfectly well, but might get one put on a hit-list....

I've just remembered that I have a couple of 1612s in the stash (red-can 6L7, intended for low-microphony audio companding), allied with 6C5s is not far off period. Watch out Carolina Eyck!
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Old 26th Feb 2020, 10:19 pm   #18
turretslug
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Default Re: Professor Theremin advert.

It looks as though the UX-120 is being used as a variable resistance in the anode feed to the heterodyne (IF) amplifier, progressively starving it of HT with movement of the "volume" hand. It reminds me of the line output transformer-fed filaments of thermionic EHT rectifiers! With their syndrome of no EHT if the LOP stage goes weedy for whatever reason. That would seem to be a topology available to Theremin at the time, so maybe that is what he did, adapted to US valves of the late '20s by RCA. Unfortunately, something rings a bell that the toobs listed are very much on the gold-star hit list of the fanatics.
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