Perma-Power Model A battery-eliminator for antique radios, circa 1949

[redwire]

I'm repairing a Perma-Power Model A battery-eliminator for antique radios. Circa 1949. 120VAC input; 90VDC 13mA and 1.4VDC 350mA output to replace "A" and "B" batteries. Uses selenium rectifiers. Power for tube filaments has two 1,500uF 3V electrolytic capacitors in a C-L-C pi filter. B+ is a C-R-C filter two 40uF 160V ea. and 1.8k carbon resistor.
I'm replacing the selenium rectifiers with 1N4005's and 0.01uF RF suppression caps.
Replacing all four electrolytics, they are a bit leaky after 65 years... and one is only 400uF.
Adding bleeder resistors.
Adding a grounded line-cord connected to the chassis. Possible problem as the filament power is chassis-grounded but B+ is floating.
Adding a primary-side fuse.
Adding a 91V 5W zener for the B+, if it's too high. Calculations show it will help the 140VDC no-load voltage.
I'm worried the filament voltage will be too high, going from selenium to silicon rectifiers. Not sure how I will handle that.

Here's pics to help anyone working on one of these.

On a sidenote:I9 checked the (label) patent 1789949 and found interesting litigation between Mallory, Aerovox, Cornell-Dubilier, Micamold in some of the history of the electrolytic capacitor. Oddly, Wikipedia says nothing about it and Google does not come up with the litigation.
http://www.leagle.com/decision/193629415FSupp279_1231
http://www.leagle.com/decision/193832425FSupp299_1247

[stj]

Re: Perma-Power Model A battery-eliminator for antique radios, circa 1949

forget the 1n diodes and get a small square rectifier with a center hole.
then you can mount it like the original to keep it looking nice.

i think the smallest like that are about 4a

shit - just looked at the schems!
never mind - use 1n4007's

[goontron]

Re: Perma-Power Model A battery-eliminator for antique radios, circa 1949

Try a 47ohm resistor to keep the filiment down if its high.
-valvedubstep on the antique radio forums.

[japlytic]

Re: Perma-Power Model A battery-eliminator for antique radios, circa 1949

Why the HT supply section is isolated is because many battery-valve/tube radios dispense with a C- bias battery and therefore have a resistor between the chassis and the B battery -ve.
For adjusting the filament supply, you can probably get away with one or more 1N5404 series rectifiers, as standard rectifiers have a near constant forward voltage from zero to maximum current draw.

[redwire]

Re: Perma-Power Model A battery-eliminator for antique radios, circa 1949

Selenium rectifiers I really hate. Selenium->Silicon always results in way too much voltage.
There is a high and low-tap on the transformer (filament) plug which measure 5.7VAC CT and 6.7VAC CT. My calcs show I will end up with 2.3-1.7VDC instead of 1.4VDC, so I'll drop it with a diode string or a small resistor.

japlytic you are right about the B+ return not going to ground, it ends up going through an 820R resistor in the radio to make C- for the output tube bias. I will leave it floating.

When the parts come in, I will update here on what I did to get it to work.

[redwire]

Re: Perma-Power Model A battery-eliminator for antique radios, circa 1949

Just a Follow up:
I replaced the filter caps with parts from Just Radios. They sell antique radio parts like axial-leaded electrolytics, mica, polystyrene, Orange Dips etc.
Replaced the selenium rectifiers with 1N4005's and found the B+ and filament voltages too high.
I added a 91V 5W zener 1N5377B to stop B+ from jumping to 140VDC under no load (until the tubes warm up).
I added an extra 1N4005 in series with the filament power to get 1.4VDC

Thanks for the help. Now it's on to the radio chassis...