Silvertone battery radio + battery eliminator

[radiotvnut]

Me and a friend went to a "pre-estate" sale by some people that someone that he knows knew (yeah, one of those deals) to see about buying an "old record player". It turns out that the record players were BPC and a late '60's cheap Symphonic console stereo. NOT INTERESTED!

While I was looking around, I saw this Silvertone battery radio on a shelf. I turned it around and saw a battery eliminator inside! This sale was actually a living estate. The homeowner's husband recently passed away after 63 years of marriage and the lady was moving into a retirement home. I asked about the radio and figured I'd get the usual "that's not for sale, the kids want it" reply. The lady said to make her an offer. I offered $15 and she asked if I would go $20, which I did.

The radio case has some veneer damage; but, it can be fixed by someone who knows what they are doing. I was more interested in the power supply than the radio as these power supplies are getting scarce and usually not very cheap on greedbay.

There is a model number inside the radio; but, I can't see it without removing the chassis. It's a basic 4 tube battery radio that runs on a 1.5V-90V pack.

I did look around for old TV's but all I found was 4 or 5 '90's BPC sets.

[Tony V]

Not a bad find. You would pay at least that much if you got the battery eliminator off of the auction site. By having this you have a power supply now to power most of the farm radios of this era. I have a few of these battery radios and they perform pretty well and are easy restorations.
-Tony

[spaceman]

Nice find, congrats! I have a thread about a Zenith, & someone was explaining about farm radios a bit. Pretty interesting, & smart, if your house didn't have electricity.

[Brian]

That is a nice looking set and I agree the cabinet should be preetty easy to bring back and hopefully the radio can be brought back. The Radio Shack catalog sight has a copy form the '30s and it shows a number of these power supplies. Sort of an industry that is short lived, like the digital to analog converters. The converter looks like it only needs a decent cleaning.

For the price you did very well, indeed.

[radiotvnut]

Looks like the radio is a model 2441, which I can't find in any of my books or on nostalgiaair.org. The battery eliminator is an Electro Products model P. I opened it and they were nice enough to paste a schematic inside the case. The date on the schematic is March, 1946. It has a power transformer and a 5Y3 rectifier for the B+ and some type of solid state bridge rectifier for the filament supply.

[AUdubon5425]

Neat! I think I still have one of these that's very rusty from being partially submerged in water for years. I'm going to have to go look - I remember wanting to save it as a guide to build one from scratch.

[radiotvnut]

I thought I'd give an update on the battery eliminator. This radio has long been fixed (just needed the usual bad caps, some resistors, and some rotten wiring replaced) and it works well. However, I just got around to repairing this particular battery eliminator.

The circuit design is such that it uses a power transformer with one 5V winding for the B+ rectifier (5Y3) and a 3.5V winding for the filament supply. The plates of the 5Y3 are tied together, making it a half wave rectifier; and, the tube gets it's plate voltage directly from the AC line. In this case, the B+ ground is "hot". Every cap was, of course, bad (a .05 uf "across the line" cap, a 20-10uf@160V electrolytic can, and a dual 1000uf,6.3V cardboard tubular cap). Also, the B+ filter resistor had risen from 2.5 Kohms to nearly 4Kohms and the bridge rectifier for the filament supply was dead. I replaced the 2.5Kohm resistor with a 2.2Kohm, 2W and I made a bridge rectifier from standard 1N4007 silicon diodes.

There is a tapped wirewound resistor in the filament line, which is connected to the three screw terminals on the front. The screw terminals are for a jumper which can be connected to bypass part, or all, of the resistor in order to obtain proper filament voltage for various tube counts. I had to bypass the resistor completely in order to achieve 1.5 VDC on an ordinary 4 tube RCA radio.

I did replace the power cord with a polarized type, with the neutral side going to ground. This power supply originally had an in-line power switch and I will place such a switch in the hot side of the line.

The only other thing that I might end up doing is replace the 5Y3 with a 1N4007 and a suitable dropping resistor. That should cut down on the amount of heat produced.

This now makes 3 battery eliminators. The other one being a similar Perma-Power unit and then there's one that I crudely built using a transformer from AES and an LM317 for the filament voltage regulator. The one I built is safer and more stable, since it uses a transformer both B+ and filament supplies and has voltage regulation.

[radiotvnut]

There is one thing that's a little annoying with this Electro power supply. When connected to this Silvertone radio, there is a little 120 cycle hum and I can hear some slight oscillation when I tune off a station.

I have a Perma-Power eliminator and the problem is not there when I use that one.

On the electro unit, I've tried bridging electrolytic caps as well as clipping in a .01 uf cap across the various outputs and nothing helps. The only thing I have not done is remove the .047 uf "across the line" cap. Like I said earlier, the filament supply uses a transformer and is isolated. The B+ supply is rectified directly from the AC line.

On the perma-power unit, both filament and B+ supplies are derived from a power transformer and are isolated from the power line. There is also no AC line cap in this unit.

[Reece]

If you ever find an older battery elminator from the '30's that has the copper oxide stack rectifiers, they often lose contact between the stack and will respond and work fine again by tightening up the nut.

[rollei35guy]

Originally Posted by radiotvnut

There is one thing that's a little annoying with this Electro power supply. When connected to this Silvertone radio, there is a little 120 cycle hum and I can hear some slight oscillation when I tune off a station.

I have a Perma-Power eliminator and the problem is not there when I use that one.

On the electro unit, I've tried bridging electrolytic caps as well as clipping in a .01 uf cap across the various outputs and nothing helps. The only thing I have not done is remove the .047 uf "across the line" cap. Like I said earlier, the filament supply uses a transformer and is isolated. The B+ supply is rectified directly from the AC line.

On the perma-power unit, both filament and B+ supplies are derived from a power transformer and are isolated from the power line. There is also no AC line cap in this unit.

I read a period article about the battery eliminators that indicated that hum was common. The article suggested relocating the eliminator. The B+ might be clean but the eliminator itself might be the source of the hum.

Do you have a scope you can check for ac ripple?

[radiotvnut]

Yes, I have a scope and that was going to be the next thing to try.