Filament batteries for portable radios & Other Voltages

An alternative to Frank's suggestion about DIY batteries is a battery eliminator. That supplies the DC voltages which the radio needs with a power supply running on house current. They are not difficult to make for someone with electronics experience - I have made a number of them.

I expect to soon build a specialized version of a battery eliminator for my first farm radio, purchased earlier this summer. A farm radio is a home radio (i.e., not a portable or an auto radio) that is powered by batteries. They are called "farm" radios because large rural portions of the country did not begin to get electrical service until after 1936, and some areas were still not electrified until after WWII.

My 1946 Motorola farm radio used a large dry battery to provide A and B voltages for the radio. Thanks to a friend I have Eveready artwork for that battery, and plan to build a replica with a battery eliminator inside the case. It will have a detachable power cord so that, when not powered up, the radio will still appear to be battery powered.

In early portable tube radios they often used a separate battery for the filaments.

 Now some tubes actually needed the correct polarity on the filament to work properly!

 When working on the old battery powered tube radios, the owners often broke or cut off the battery connectors for the A, B, and C batteries. Some radios used separate batteries for each voltage also. Don't be surprised to see the C battery + hooked to the B - connection or the filament A- connected to the B- . It was they way they designed the radio.

BE SURE TO ACTUALLY TRACE THE WIRES BEFORE CONNECTING BATTERIES TO THE RADIO. There was NO STANDARD COLOR CODE back in that era.

The mistake of hooking up B+ to the filament can cost you an entire set of tubes. I saw it happen to another person, and I did it myself only once when I didn't trace the wiring out.  .
 For some odd reason 1.5 V tubes do not like 90 V  of B+ on them. This was a very costly lesson for me at the time too. 

Be sure to find a schematic for the radio. It will help you ID the correct wires, and many OEM service data books showed the color codes for that model of radio. That being said, however, do not trust the color coding on the wires you can readily see. Red can turn pink,  orangeish or brown. Yellow can look like white or cream color, slate like black, and some used wires with colored tracers. UGH! , well you get the idea. 
  This is especially true if the wires have been exposed to sunlight for a long time. The cloth or silk covered pushback wire did not have really good color fast dyes used on it. Often you can find the true color of the wiring under the chassis, but then again, the wire insulation dyes used can easily fade with time. So actually trace the wires out. Then MARK THE WIRES with tape, zip tie tags or what have you and use an indelible marker (like a Sharpie) to mark the tagging.  I found several times that the wire I thought was one color had actually faded and changed color, even under the chassis. Smoke, heating oil fumes, etc. can change the colors too, from their chemical interaction.

Now you can have a B battery made up or DIY by series connecting a stack of 9V batteries in series. I have made my own C batteries by series connecting a number of AA batteries and then encasing them in heat shrink. Often you can have a company make the packs up if you have doubts on your construction capabilities. (Batteries Plus can make up packs. Not a sponsor nor an ad for them. Just a source that is pretty common).