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 Post subject: Telephone Crank Magneto Transceiver
PostPosted: Dec Sat 28, 2019 6:52 am 
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Joined: Feb Sat 16, 2013 5:08 pm
Posts: 934
Location: Ft. Collins, CO.
I'm entertaining the idea of a subminiature tube transceiver, powered by an old 5 bar telephone magneto/generator. They output 110 volts AC, at a lower frequency (I expect 20-30 Hz).

I'd be using the Russian 1J29B (http://www.ha3oc.hu/TUBES/1J29B.pdf) for whatever I can. I also have a 6 volt heater dual triode type I could use alongside the 1J29B tubes.

The big question for me, is whether or not there is a way to do it without a transformer. The main issue being that I need to supply a B+ voltage, which will require a full wave rectifier. For such a rectifier, I would wire two 1J29B tubes to act as diodes- But those circuits require a transformer.

My target B+ voltage would be around 60 volts, so almost half of the input AC voltage. I think this should make it easier, but I'm still not sure if I can get around the transformer.



Crossing the bridge before I get there:
Quote:
So far, here is what I've calculated (hopefully correctly):

The filament resistance of the 1J29B is 38 ohms, 62 mA current draw, and 2.4 volts. So, two tubes, I could connect them in series with a 1700 ohm resistor and directly drive the filaments from the generator. The resistance of the resistor will just drop by 38 ohms each additional tube.


The issue with directly driving the filaments, is that then I can't use the generator output in a rectifier circuit unless said circuit has a transformer- Which I'm trying to avoid.

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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Dec Sat 28, 2019 9:17 am 
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Joined: Sep Mon 16, 2013 2:42 am
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Location: Tucson, Arizona U.S.A.
These tubes are designed to run from batteries. Running the filaments from AC will cause intolerable hum; they must be powered by DC. Use a selenium or silicon bridge rectifier on the output of your generator and run everything from that. To get a lower voltage, crank slower. You will need some sort of indicator to know when you are turning it at the right speed in any event.

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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Dec Sun 29, 2019 6:52 am 
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Joined: Feb Sat 16, 2013 5:08 pm
Posts: 934
Location: Ft. Collins, CO.
Any thoughts on winding my own transformer? Perhaps it's impractical?

I could potentially run the whole radio from the B+ voltage, with a voltage divider to run the filaments, no?

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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Dec Mon 30, 2019 1:10 am 
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Joined: Sep Mon 16, 2013 2:42 am
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Location: Tucson, Arizona U.S.A.
If you wind your own transformer remember that the frequency from this generator is very low and depends on how fast you crank it. The transformer will be larger than what you are used to seeing, even in 25 Hz sets. That, of course, means at the same power level. The standard transformer winding equations apply.

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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Dec Tue 31, 2019 12:03 am 
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Joined: Feb Sat 16, 2013 5:08 pm
Posts: 934
Location: Ft. Collins, CO.
After taking some time to get a rough idea of transformer size, etc, I've decided on an old power transformer for a Stromberg Carlson instead of taking the time to make one (just flat out impractical- Which I should have known). At a moderate crank speed, I get 2 volts out of the filament winding. Just about perfect for this project.

I put together a very hasty rectifier circuit with the 1J29B tubes, and am very pleasantly surprised.

Because the tubes use a direct wire filament, they turn on almost instantly. The result is that the rectifier starts operating within the first revolution of the crank. I can charge up a capacitor to at least 260 volts, although that appears to be the limit and take a while to charge up.

With an 80 volt neon tube across the capacitor, it flicks on every few seconds while turning the crank. Based on that frequency, it should have plenty of power to run a radio circuit.

Image

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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Dec Tue 31, 2019 5:12 am 
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Joined: Dec Sat 24, 2011 9:17 pm
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Location: Vancouver Island, Canada
Fascinating! 8)

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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Jan Sun 19, 2020 9:04 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 12017
Location: Powell River BC Canada
Magnetos have some quirks. When cranked the shaft is spring loaded so as to
close a contact on the end. This prevents the magneto from loading the
phone line when not in use. That contact isn't very good, but it doesn't have to
be.

Other things to look for are that all the magnets are put on correctly.



If not, and one is backwards, it will subtract form the voltage.
Attachment:
Five Bar Phone.jpg
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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Feb Fri 21, 2020 5:31 am 
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Joined: Sep Sat 19, 2009 1:51 am
Posts: 29
Location: Australia
You'll be well advised to use a voltage regulator feeding the filaments, otherwise you crank too fast and they're gone !
I repaired a 32 volt radio for someone living a great distance away. It had a series string of heaters, and when I had the radio working, I found that there was 10 to 15 % too much heater voltage. I fitted a TO3 power transistor with a simple Zener and resistor, under the chassis. Worked fine, the heaters were on the correct voltages, and the reg ran nicely cool. But I didn't count on the 32v polarity being reversed. It happened, in spite of my notes and a piece of tape across the power plug. The reg shorted. When I received it back a year later, I replaced the blown up bits, (all the tubes survived, AND the dial lamps, but this time I fitted a heavy diode in series with the power input. He comes into town once a year for the annual car swap, so its waiting until that time to be collected. I couldn't find my 32v power supply that I built for checking the 32 volt TV sets, so I had to build up a regulator which runs from two spare 20v solar panels in series. No battery on the system, so I have to wait for a sunny day and periodically I check that the radio still works.


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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Feb Fri 21, 2020 5:53 am 
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Joined: Sep Sat 19, 2009 1:51 am
Posts: 29
Location: Australia
I had another thought. A few years back, I had ideas of building a radio to run from my 24 volt off-grid house/workshop solar supply. Realising that the old hybrid 12v car radios used a special series of tubes which were designed to run from a low HT supply, I did some tests with more common tubes. I found that most tubes will work quite happily from low HT voltage. So in light of your own situation, something just now occurred to me.
You may realise that where directly heated tubes are used, the filament voltage is commonly used as the grid bias voltage. You have to ground the positive side of the heater and then you have a negative supply for the grid bias.
What the light bulb idea was, if you have for example five stages in the receiver, that you put all of the stages in SERIES across the rectified magneto output. Each stage is self contained, running from 1/5 of the supply, and the filament and HT voltages for each stage being derived from 1/5.
If you DON'T do it this way, you'll have difficulty biasing the tubes, if you have full HT on them, and the tubes in series.
You'll need a few extra caps to bypass things to ground, and to isolate the tuning gang, but it could be an interesting and unique concept. The whole set will have to run from DC, and regulating the high DC voltage to keep the filaments safe will simplify the circuitry. Have fun!


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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Feb Fri 21, 2020 7:16 am 
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Joined: Sep Mon 16, 2013 2:42 am
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Location: Tucson, Arizona U.S.A.
If you connect the filaments in series, the plate current of the most positive tube flows through all the other filaments. The plate current of the second from the top one flows through all the filaments below it in addition to the plate current of the top tube. As you go down the string, the plate currents add. If this ends up adding a significant amount to the rated filament current, it shortens the life of those tubes. That's why 3-way radios usually have a network of resistors across the filaments of the lower tubes.

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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Feb Fri 21, 2020 4:21 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 14740
Location: S. Dartmouth MA 02748-1225 USA
RS-1 and a GN-58. Borrow the concepts. Or get one and fix it up. That should keep one well exercised during a DX contest...

http://www.militaryradio.com/spyradio/rs1.html

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 Post subject: Re: Telephone Crank Magneto Transceiver
PostPosted: Feb Fri 21, 2020 7:53 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 12017
Location: Powell River BC Canada
The GN-38 is nice as it is smaller. Additionally, the old 3 and 5 bar magetos,
can be rewound to give you lower voltages.

If you stare long enough at the rotor of the telephone magneto, you may be
inspired to more. :)

My father's job occasionally was to travel to places to oversee a cut over of
magneto based systems to dial. He brought back the occasional
magneto subset for us to play with.

Here is a ghetto ringing machine.
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VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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