https://www.skywaves.ar88.net/homebrew/ARC-5_PS/ARC-5_PS.html

Near the bottom of the page is this:


This is a reasonable approach for the high voltage, but it has a possibly critical error. The output voltage will be a little under 340 Vac. I don't have any experience with these radios, but that is a significant increase over the numbers so far in this thread. That is why the high voltage transformer in #20 is 1:1.4 instead of 1:2 (1:1 transformers followed by a voltage doubler).

ak

 

REALLY, the ARC5 receiver will work with a lower V+ supply! so just use a 24 volt transformer and a voltage multiplier circuit to get about 100 volts (no load) for the high voltage, and use the 24 volts to supply the tube heaters. I have used the receiver in a 12 volt car and it does work adequately with that 28 volt dynamotor fed by the "12 volt" power from the lighter plug. BUT you don't get as much volume from the audio output..

 

https://www.skywaves.ar88.net/homebrew/ARC-5_PS/ARC-5_PS.html

Near the bottom of the page is this:
View attachment 367335

This is a reasonable approach for the high voltage, but it has a possibly critical error. The output voltage will be a little under 340 Vac. I don't have any experience with these radios, but that is a significant increase over the numbers so far in this thread. That is why the high voltage transformer in #20 is 1:1.4 instead of 1:2 (1:1 transformers followed by a voltage doubler).

ak

Since 24vac Transformers are easily available, and 26 vac transformers are harder to find, will a 24vac unit "float" closer to 26vac, and will they be acceptable for this useage??

 

Since 24vac Transformers are easily available, and 26 vac transformers are harder to find, will a 24vac unit "float" closer to 26vac, and will they be acceptable for this useage??

If you are asking about two back-to-back transformers acting as a single 11 isolation transformer, it doesn't matter what the secondary voltages are as long as they are equal. Also, 25.2 Vac is a commonly available value.

Note that for the same overall output power, higher secondary voltages mean lower secondary currents.

ak

 

Military radio equipment intended for 28 volt systems, ESPECIALLY the ARC5 receiver, is quite forgiving of lower supply voltages..It will operate off of only 20 volts, not quite as well, but it will still receive. The audio power output will be less, but that is to be expected..
The "28 volts" rating is when the generator in the plane is putting out full power, the 24 volts is when the radio is only running off the battery with no generator running. And the 12 volts was running in my car back in 1965. That radio has a dynamotor clearly marked "28 volts". YES, and the tubes did take longer to warm up. I did rewire the tube heaters all in parallel so that 12 volts would power them properly. BUT I could not get a 12 volt dynamotor.

 

If Im using 2 back to back transformers, a diode bridge and capacitors, (as in Post #21 illustration)what should the fuse be on the incoming 120v line?

 

If Im using 2 back to back transformers, a diode bridge and capacitors, (as in Post #21 illustration)what should the fuse be on the incoming 120v line?

Whatever the fuse would be if the load were connected directly to the mains, plus 10% to 25% to cover transformer losses.

ak

 

Are transformersthat terribly expensive currently?? Is there a total lack of discarded electronic equipment? I have found that used transformers are often very long-lasting, because they have already passed the comon short-term failure modes ages.
Of course, it may be that I have developed an instinct as to what sort of useless equipment will yield the most useful components. Buying stuff new would be painfully expensive in most instances.