Building an 80-0-80 supply for double current teleprinters

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M1ECY
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Building an 80-0-80 supply for double current teleprinters

Beitrag von M1ECY » Mi 22. Nov 2017, 21:17

Hi All,

Taking a break from the 444 for a while - it needs a safer and less space consuming way of providing line current.

So I have started to make my own power supply.

I have rewound an old transformer I had laying around here, and have started converting some old panel meters I had laying around.

The transformer started out in life as a 9-0-9 V unit, after dismantling the transformer and unwinding the original secondary - from doing this I could calculate the number of turns I needed to give me the required output voltage.

700 turns later, with a centre tap at 350 turns, and the secondaries are completed.

I include a picture of the first meter for the +80v supply - will put up more pictures as soon as I get the time.

Cheers
Sean
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G3WSD
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Re: Building an 80-0-80 supply for double current teleprinters

Beitrag von G3WSD » Sa 25. Nov 2017, 09:49

Hi Sean,
The way I now build my 80 volt supplies is to use a 12VA transformer with two 15 volt secondary windings connected in series and connect a FW voltage doubler using 2 diodes and 2 capacitors to the output. As you don't very much current, it doesn't sag much under load. From memory I think I ended up with 78 volts while drawing 40mA. Then I use two transistors in a sort of half bridge circuit to switch the current through the teleprinter electromagnet. The dual supplies are really only useful if you are going to use a telegraph relay or the Tx contacts in a machine.
73, Alf


G3WSD
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Re: Building an 80-0-80 supply for double current teleprinters

Beitrag von G3WSD » So 26. Nov 2017, 10:03

Hi Sean,
I've just checked the order details and the transformer was actually a 6VA 2 x 15 volt. I also bought a 1.2VA 4.5 volt + 4.5 volt one to provide a nominal 12 volt supply for the other part of the single to double current converter circuit.
73
Alf

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