Comments on Strange Tube Circuit

I found this schematic in a pile of experimental documents left to me by my Uncle. There is no reference to its purpose.

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Can any please advise how the circuit works, any obvious use, and what the transmitting frequency and waveform might be?

IOW what would the output look like on a CRO?

Thank you,

Robert Stevens

Reply to
Robert Stevens
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appears to be a linear amplifier for RF signals

like the input but larger amplitude.

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umop apisdn
Reply to
Jasen Betts

On a sunny day (9 Jun 2015 09:48:24 GMT) it happened Jasen Betts wrote in :

With an Ra of 270 k in the tubes, 'RF' would be in the audio range, not counting the capacitance from 'antenna' to ground.

That is without looking up those tubes.

It is a practtical joke probably from some old poster here ;-)

8 Henry, nice choke.. OK thw current is next to nothing so no saturation in that iron.

Why all the ballast resistors of 1W each, mm so there is current. I figured it out:

It is a room heater. It transmits in the IR range.

:-)

Reply to
Jan Panteltje

On a sunny day (Tue, 09 Jun 2015 11:25:10 GMT) it happened Jan Panteltje wrote in :

Right, and 'ag' must be short for 'agw' or 'antro-something global wo^Harming'

Reply to
Jan Panteltje

What if the antenna is half wave? Doesn't that make it a VHF linear?

Cheers

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Syd
Reply to
Syd Rumpo

No.

The impedance level, stray capacitances and tube properties limit the frequencies to the audio range only.

It is just an audio voltage amplifier with a maximum output of about 300 Vpp.

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-TV
Reply to
Tauno Voipio

With those resistor values, it's an audio amp.

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John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 
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Reply to
John Larkin

Yes. With a 6-meter ham band whip antenna load.

Reply to
John S

This is strange. I had the impression it was designed to transmit radio frequency.

Are you saying this is not possible according to the schematic?

Any tube experts here that can confirm?

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Robert Stevens

Reply to
Robert Stevens

The 51" antenna equates to about 230MHz.

Is the curcuit capable of adding this frequency, as a carrier, to the input signal and transmitting same?

If so, it would presumeably need to oscillate at that frequency as well as amplify.

Robert Stevens

Reply to
Robert Stevens

Except that whip antennas are 1/4 wave long or thereabouts, so it resonates about 58 MHz.

There is such at thing as a plate modulator, where a big audio amp modulates the plate voltage of the transmitter's final stage. Way back in the day, that was attractive because the TX final could operate Class C, without causing unacceptable audio distortion.

(Amateur transmitters were regulated by the DC power input to the final stage, so you could get a lot more RF that way while still staying legal.) AM is inefficient, however, because only half the TX power is in the audio sidebands. SSB is a much better use of both power and (especially) spectrum.

A plate modulator often used the same type of tube as the TX final, because it takes a _lot_ of audio power to do that.

The output tube of the circuit you posted runs at way less than a milliamp, so you aren't going to do much modulating with it. Also a plate modulator doesn't connect right to the antenna, because there's a tank circuit and output filter in the way, so the antenna isn't sitting at the plate potential of the TX final stage, and jiggling it up and down won't do anything.

(Takes me back, sure and it does...I learned a lot of electronics from my trusty 1966 ARRL Handbook. Just about killed myself building a TX power supply when I was about 14.)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

Probably, it never worked at all. Uncles weren't always right.

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John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

I was never interested in being a ham - all they seemed to do was talk to other hams about being hams - but I did read the Radio Amateurs Handbook when I was a kid, and learned a lot. I have the 1946 edition here. No, I didn't buy it new.

I did manage to almost kill myself in other ways. I got across a tube TV power transformer once, the ends of the B+ secondary, and that left me shaking for days. Kids nowadays are afraid of touching a board powered by +5 volts.

And we did find a shopping bag full of shotgun shells in an empty house one summer...

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John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 
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Reply to
John Larkin

An end-fed half-wave whip would be 115MHz and fairly high impedance (high voltage drive), although I agree that the 270k anode resistor is still way too high.

Cheers

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Syd
Reply to
Syd Rumpo

A whole lotta nothin'.

It's still possible it could be an RF transmitter, but not from what is shown here. Example: using parasitic grid or cathode wiring lengths as tuned resonators. Then you could have a tuned-plate, tuned-grid oscillator at the ~58MHz others have mentioned. Piss-all power output, would be lucky if it's even DX-able (also, AM or CW if that).

It would do just fine as a high gain audio preamp, if the output were connected to another jack. Why it says antenna, who knows. Maybe he wanted a source of electric field for other reasons. Maybe he didn't have a clue whatsoever!

Tim

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Reply to
Tim Williams

Any other documents in there with a black box labeled "tube amp" connected to an antenna?

Like the input, only moreso.

Mark L. Fergerson

Reply to
Alien8752

From the replies so far, I understand the circuit (as drawn) is an audio amp that feeds 300V at less than a mA to a 6 metre band whip antenna.

I have no explanation for this apparent discrepency, and my uncle is no longer with us. Some thought he was a bit of a misunderstood genius.

I am wondering, however, what is the purpose of the tank circuit and filteryou mentioned?

Doesn't this imply a specific operating frequency?

Robert Stevens

Reply to
Robert Stevens

That may well be true, but if so, this circuit isn't one of his best, or wa s meant humourously. Do you have others you could post?

It's to improve the spectral purity of the transmitter, match its output to the antenna for maximum efficiency, and isolate the antenna from the very dangerous plate supply of the transmitter final stage.

Well, most any given transmitter at any given moment will be operating in s ome narrow band, e.g. 980 +- 3 kHz for an AM talk radio station. You design the tank and filter/matching network for the desired frequency range.

There are exceptions, e.g. ultrawideband radar, but they're rare.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Thank you for your further explanation.

I still cannot understand why anyone would mismatch the wavelength of the antenna to the audio bandwidth of the amp.

My Uncle was an electronics engineer with a shed full of test gear.

Apart from that, I am wondering if applying 300V directly to an antenna was common practice in the 1950's.

Maybe it was a trade-off that suited tube circuits? More voltage and less current vs. less voltage and more current of today's solid sate devices.

Robert Stevens

Reply to
Robert Stevens

This is just a basic broadband amplifier. Can be used for any frequency. Th e antenna length specified is ad hoc I would say. The amp itself would work for any frequency the tubes and the coupling caps can do.

Uses ? Hard to say but it reminds me of something. Old days of TV shops, se lling TVs, new or used. One shop took an amp, stuck an antenna on the roof up high and ran the signal through an amp into an antenna in the showroom. All you neeed was a little piece of wire on one of the antenna terminals an d you got a perfect picture on all channels. the signal transmitted from th e antenna swamped anythong coming in off the air along with any multipath. Worked pretty good.

the only clue in that circuit is the antenna legth, and it doe snot say muc h. At one frequency it is a 5/8 wave, at another 1/4 wave and so forth. The re are no other frequency determining components in it. Eother he was a kid not knoing, or it was meant to be broardband. The 51" antenna can transmit at any frequency, but efficiently at only certain ones.

That's my take on it.

Reply to
jurb6006

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