I’m looking for an elegant solution to power an old radio with 220v dc

[w0pjb]

The bc-348 radio was powered by a dynamotor with output rated at 70ma @ 220V dc according to spec.
I have 120V AC on the house mains. I’m keeping the radio on DC power.
I have one schematic (attached) I’m looking at but that involves 2 transformers which I could work with but there has to be a way to get there with a switch mode power supply with maybe a zenor diode. Designing that is way beyond my skillset.

Here is the outline for the solution for 2 transformers.
Transformers T1 and T2 are low-voltage
transformers with 120-volt primaries. They are
hooked up in reverse so that the high voltage
appears at the output. Use transformers with
12-volt, 2 amp secondaries for 12-volt operation; with 24-volt, 2 amp secondaries for 24-volt
operation.
PNP power transistors are 2N6109 or equivalent. These must be heatsinked. Check the data sheet for your transistors to see if the heatsink tab is connected to internal circuitry. If so, and if your “dynamotor” is to be built on a metal panel or chassis, you’ll need to add mica insulators under them. Diode D1 is a 500-volt (or better), 2 Ampere unit (1N4007 or equivalent). Capacitor C1 is a 40-80 uF, 300-volt electrolytic. Resistors R1 and R2 are 10,000-ohm, 1-watt.

 

[Martaine2005]

Maybe an easier way is with a 220V-120V voltage converter, Europe to USA. It’s essentially a single transformer which you can then use in reverse. Add the bridge rectifier and smoothing caps for DC.
Just an idea to get the thinking caps on..

Martin

 

[Harald Kapp]

Any 120 V to 220 155 V transformer (or 220 155 V to 120 V transformer in reverse as suggested by Martin) will do with the help of a rectifier and smoothing capacitor. [Edit: corrected transformer ratio to account for peak values.]
The rectifier and capacitor will be needed in any case. The single transformer is a so much more simple solution than an SMPS.
You can't use a standard mains transformer with an SMPS: mains transformers are designed for 50 Hz or 60 Hz operation. An SMPS operates in the kHz range. The standard mains transformer will not operate well in that frequency range and would be way to big, too. SMPS transformers usually are small ferrite types.

 

[bertus]

Hello,

When you use a 220 V to 120 V in reverse, the output voltage will be 220 V AC, when rectified the voltage will be about 310 Volts DC.

Bertus

 

[Harald Kapp]

I must have been still a bit sleepy. Of course, after rectifying we'll have the peak value which is sqrt(2) times the RMS. Therefore the transformer ratio needs to be changed. I updated my post #3.

 

[Harald Kapp]

According to this website (German) the elegant solution would be to use a mains power supply NG-V, if you can find one.

 

[bertus]

Hello,

Wich version do you have?
Here is a manual for the E,M and P version:
http://www.shortwaveradio.ch/lib/exe/fetch.php?media=manuals:to_08-10-119.pdf

You will still need an 28 Volts for the heaters of the tubes.

Bertus

 

[w0pjb]

I have the bc-348R.
So it appears they have it right with the original solution of 2 tranformers. I would have to hook up the oscilloscope after I have it wired in and see what I get.

 

[Martaine2005]

You will still need an 28 Volts for the heaters of the tubes.

Apparently, it was common to wire all the series-parallel heaters in parallel. This meant the heaters run on 6.3Vac rather than the original 24v/28vac.

Martin

 

[bertus]

Hello,

Apparently, it was common to wire all the series-parallel heaters in parallel. This meant the heaters run on 6.3Vac rather than the original 24v/28vac.

It depends on the type of tubes/valves.
There are tubes/valves that have the same current, but different voltages.
There are tubes/valves that have the same voltage, but different currents.

Just look in the datasheets of the tubes/valves for the type used.

There are a couple of numbering systems for vacuum tubes/valves:
https://webspace.science.uu.nl/~tel00101/FotoAlbum/RadioCorner/Articles/TubeTypes.htm
https://www.tubemuseum.org/SearchResults.asp?Cat=30

Bertus

 

[Martaine2005]

This is an interesting read for the OP.
How to put a modified unit back to original.
https://www.radioblvd.com/bc348_dynamotor.htm

Martin