Hi, I found Philco Radio 47H for sale pretty cheap in my area. Cabinet looks in good shape it has 2 speakers and as far as I can tell from the pictures this is a 47H model which is 120 VDC only. I have a couple of questions before buying it, is it worth restoring since I'd have to build a 120v ac to dc converter to operate it, and how difficult is it to build one? Second, the owner said he plugged it in, probably didn't realize it was DC only, and stated it was loud static coming out of the speakers. Could he have damaged the radio by plugging into AC directly? Thank you,
Yes the radio possibly could suffer from being plugged to AC, but not necessarily.
Building the AC/DC could be as simple as building a rectifier bridge and a capacitor. If you use a Pi-filter, 2 caps and a resistor, the resistor could take care of dropping out the excess voltage.
I did some back of the envelope calcs and on 50W load to drop to 115vdc from about 170vdc rectified I'd need 25W resistor. It seems I'd need to use a transformer but i think 120vac to 80vac are pretty rare/expensive, at least i have not found one yet.
What about using a half wave rect instead of full bridge look into using a bucking transformer (24 volts?) to reduce the ac input to the half wave. Good luck David
If you were to use a capacitor to drop the voltage first then you could rectify the rest without losses or much losses.
Also tube rectifiers drop some voltage due to the higher plate impedance.