[Radioengineer]

I have a Philco 42-360 that needs a new power transformer. The schematic shows 320 vdc on the output of the rectifier 84. I`m not sure what the current requirements are needed to operate this radio.

[klondike98]

Welcome to the Phorum!


Can't answer your question but someone surely will be able to help. The service bulletin for the radio is available at http://www.audiophool.com/Philco.html .

[Radioroslyn]

Hi and welcome to the Phorum,
Your looking at about 60ma. They're pushing that 84 pretty hard.

[morzh]

Well....let's try to do the first order calculation.

The rectified voltage is 320V. The dropout across the field coil's DC resistance of 1.7kOhm is 130V (down to 190V). We're lucky we have the numbers directly before and after.
This makes the total of 130V/1700 Ohm = 75mA.

Now each half-winding will conduct the same average current exactly 1/2 of the period that makes it 38mA average per half-winding.

Add a margin of say 50% (or whatever you are comfy with), this will make it 57mA. I'd say, that is enough.

(Almost radio engineer)

[morzh]

PS. Saw Terry's reply. Hey! I was pretty darn close!

[Radioroslyn]

Hey Mike,
I do the rough calculation by multiplying the # of tube not counting the OP or rectifier X 5 (ma) If and tube has more than 1 section + 5 more ma per, diodes don't count. OP= 20ma. So 7 tubes X 5ma + 20= 55ma + a little for good luck=60ma.
Then I look up the tube specs to see if the rectifier can handle the current load. 84 is good for 60ma.

[morzh]

Terry

I'd do the same, but when I'm lucky to have the Voltages directly shown along the current path, with known resistances for the dropouts, I use those - takes the guesswork out of the process.