Truetone battery-powered tube "farm" radio

[Chad Hauris]

This is a battery powered tube radio I got at the local hamfest for $1.00 several years ago. All of the wiring was rubber and had to be replaced, and I put in new caps. I'm using 10 9-volt batteries for the B supply and 1 D cell for the A. Temporarily I'm using a 9-volt battery and potentiometer to supply the 4.5 volt negative bias voltage till I can get some more battery holders for some AA cells. It works very well and has plenty of sound output.

[stusnyder]

having a number of battery radio's, I was shocked when I checked out the prices of 9 volt batteries I went and purchased a ARBE III and I'm really happy with it.

[radiotvnut]

I have two battery eliminators, from the '40's, that have the various plugs for different radios. IIRC, one is a perma-power and the other is an Electro. One has a solid state rectifier and the other uses a 5Y3 tube. I also have one of the AES kits.

[Reece]

That's pretty neat, Chad. Not a whole lot under the chassis when it doesn't have a power supply, eh? As to the price of 9-volts, dollar store or Big Lots type stores have off brands cheap which are fine for this purpose. And it's pretty easy to make a power supply for such a set and lots of room inside the cabinet for it. Looking around the electronic surplus places on line you can often find a 1:1 transformer (120 in/120 out) to build the B supply around. There were some like that with low voltage windings also a while back, for just a few bucks each. I bought some of these and used one to make a B supply and its 7 volt (open voltage) secondary was fine for three 6.3 volt heater tubes.

Edit: for example, I just found this dual primary transformer for $5.95 (I have no connection with this vendor.) It has two electrically separate primaries. One can be used for the input from 120VAC. The other primary can be the 120VAC secondary for your high voltage. The secondaries are two 10 VAC. They could be reduced in voltage and solid-state regulated for filament and bias. Would take a little experimentation but there are circuit diagrams out there that would be a basis to start.

http://www.alltronics.com/cgi-bin/it...ormer-DST-7-20

[captainslack]

The current issue of The Monitoring Times has an interesting article about wind powered farm radios such as this one. Pretty interesting read as I'd never heard of such a thing before.

[radiotvnut]

Several years ago, I built a 90V/1.5V power supply, using two 12.6 volt transformers wired back-to-back. These transformers were from rat shack and were reasonable at the time. For the filament supply, I used a standard bridge rectifier and filter circuit feeding an LM317 adjustable voltage regulator IC. For the B+, I used a standard bridge rectifier and PI type filter network. I didn't add any type of voltage regulation for the B+; but, you could add some zener diodes in order to keep the B+ at the required level.

Obviously, the advantage of a solid state power supply is the voltage regulation; which, is really not there on the older battery eliminators from the '40's and '50's.

[Chad Hauris]

Thanks for the information about solid state power supplies. I probably will keep this one just running on batteries since I seem to get a better signal-to-noise ratio for some reason especially on distant stations than on AC-powered radios. Plus for some reason I just like knowing the fact that it's running on batteries!
I may upgrade to 60, AA cells using some 8 AA battery holders plus a 4-cell holder. I saw a real good deal on AA cells in a mega-pack recently.
I'll just have to see how long the 9-volts last.

Here is a video showing the radio playing:

http://www.youtube.com/watch?v=5UNkcby2Ox0

[bgadow]

Nice looking set! I have a few farm sets that are in working order. I built a B supply in a cigar box-it must be 10 years old now, I think the 135 line is down to 90 something volts now. Time to invest in a new batch of batteries. You can get some strange looks buying that many at one time!

I have a couple of those old battery eliminators and really need to dig them out and get them going again. I *think* I've learned enough since stashing them away to now make them work!

[radiotvnut]

I suspect that on this battery pack, the "D" cell filament battery will die much faster than the others. For the filament supply, you could wire at least two "D" cells in parallel, which would give you more current.

[Chad Hauris]

I do have an RCA portable tube radio which has space for two 1.5 volt cells in parallel (those old kind of 1.5 volt cells which are about the diameter of a "D" cell but about 1 1/2 times as long) but I've read that parallelling cells like that can cause problems where a stronger cell can end up discharging through a weaker one...not sure if that is really true or not. Using a diode to isolate the cells wouldn't work I wouldn't think because the voltage drop of the diode would eat up most of the 1.5 volts.

I read that a "D" cell has 12,000 milliamp/hours and I figured the total filament draw of the radio is 400 ma so the cell should last about 30 hours, or what some people have said the 9-volt batteries would last in this service.

What would be great is if you could get the really big 1.5 volt cells with the screw terminals...if they still make them I'm sure they're really expensive now.

[stusnyder]

I read that a "D" cell has 12,000 milliamp/hours and I figured the total filament draw of the radio is 400 ma so the cell should last about 30 hours, or what some people have said the 9-volt batteries would last in this service.

What would be great is if you could get the really big 1.5 volt cells with the screw terminals...if they still make them I'm sure they're really expensive now.[/QUOTE]

You can still get all the old style batteries here:
http://www.batterycentralmall.com/Ba.../Eveready.html

[Chad Hauris]

I looked at that site and they must have made the large 1.5 volt cell until very recently as there was an Energizer alkaline version but it looks like it's been discontinued.

Also I saw the large 9-volt batteries that one of my old transistor radios use but they are around $22.00! I think I'll just convert the battery clip on that one to a modern 9-volt and even if the modern 9-volt doesn't have as much current I can replace a lot of them for the cost of one of the old style.

I guess they still do have some of the high-voltage B batteries and I might keep those in mind for smaller portable tube radios which don't have as much room for modern batteries inside. I wonder what applications these are mostly bought for these days?

I'll keep using the radio and see how long these cells last I'm using now.

[electroking]

A four-tube radio like this is probably pulling no more than 200 mA from the A
battery. I was surprised to read the figure of 12000 mA*hour (that's a product,
not a division), but that seems to be true. Putting two A cells in parallel is likely
to more than double A battery life. Good luck!

[bgadow]

I've wondered about those oddball batteries myself, and how they can justify making them at all. The shelf life can only be so long. I haven't checked out AES for several years, but I remember back when I first got their catalog in the 80s they had those B batteries and they were quite expensive then. Almost that long ago I was in a freight salvage store and they had an odd assortment of older style batteries. I seem to remember one being about 2" square and 22volts. I bought most of them but never did put any to good use.

[radiotvnut]

The local parts house had some late production 67.5 volt and 90 V "B" batteries for the portables of the '40's and '50's. I was going to buy one for a radio I had at the time until they told me the price (pushing $30). I decided that I didn't need to go that route and that if I wanted to run that radio on batteries, a bunch of 9V transistor radio batteries wired in series would do just fine.