Rebuilding Vintage A and B Batteries

In the early days of electronics, vacuum tube devices were powered by batteries as many homes had not been wired for electricity. The batteries used for powering these early electronic vacuum tube devices were classified as "A", "B", and "C" batteries.

The "A" battery was used to provide power to the filament of a vacuum tubes in the device. Typically this battery was low voltage (usually between 2 to 7.5 volts) but required a high amperage to power the vacuum tube filaments. Lead-acid types, like classic car batteries, were used initially until better high amp-hour Zinc-Carbon batteries were developed.

The "B" battery was used to provide the plate voltage of a vacuum tube. These were typically of the Zinc-Carbon variety with many cells wired in series to provide the low amperage and high voltage (usually 22.5, 45 or 90 Volts) required.

The "C" battery was used to provide bias to the control grid of a vacuum tubes. This was typically a low voltage and low amperage (9 Volts  with several 1.5 Volt taps) Zinc-Carbon battery. The C battery was largely done away with as it was soon discovered that the needed voltage/current bias could be derived from the "A" battery using a grid leak resistor or voltage divider biasing.  

Pictured above are examples of an "A" and "B" battery I just pulled out of a 1947 TRAV-LER Model 5020 portable vacuum tube radio that I am in the process of restoring. Two "A" batteries were connected in series to provide the required 9 Volts for the tube filaments. In addition, two "B" batteries are connected in series to provide the required 90 Volt plate voltage. No "C" battery is required as the Model 5020 uses grid leak resistors to provide required voltage.

​"Old Time Radios! Restoration and Repair" book on Amazon

I consult this book often during radio restoration. I grew up in the transistor and diode era and this book taught me a lot about vacuum tube and selium rectifier technology.

​My Goal

I wanted to be able to power my vintage radios, such as my Trav-Ler Model 5020, from both the AC line and battery power so as to test all circuitry. In addition, I wanted to also be able to power any radios I might purchase that require battery power only. 

Disassembly

Below is a picture of one of the A Batteries I am going to rebuild. It has a nominal Voltage of 4.5 Volts DC. My Trav-Ler Model 5020 required two of these batteries in series to provide the high Amperage 9 Volts required to power the filaments of the vacuum tubes.

I carefully used an X-Acto knife to open the bottom of the cardboard box that houses the battery cells so as not to rip or tear it. I want to install the replacement batteries in the cardboard shell so as to give it a "vintage" look. As you can see below three 1.5 Volt cells are contained in each "A" battery. They are wired in series to achieve the 4.5 Volts DC. The middle cell is insulated from the two outer cells by a cardboard divider. This is to prevent shorting out of internal battery cells as the outer metal case of each cell serves as the negative connection.

I wear disposable Nitrile gloves during the "A" and "B" Battery disassembly process so as not to expose my hands to harsh chemicals. In addition, I disassemble the batteries on disposable paper plates so as not to get the dried chemicals all over my workbench.

Yuck! Here is the contents of the "A" battery. Notice the chemical leakages on the outside of each battery cell. The dry chemicals have impregnated the outer cardboard case of the "A" battery and internal cardboard spacers. The only thing that I can salvage is the top connector of the battery as it is made of Phenolic resin that can be easily cleaned. I used a pencil to mark a plus sign next to the positive terminal of the battery connector. Disassembly of the second "A" battery was the same.

Here is the picture of one of the Burgess M30 "B" batteries. Its nominal Voltage is 45 Volts DC. Two are wired in series to achieve the 90 Volts needed for the plate voltage of the vacuum tubes in the Trav-Ler Model 5020. 

Once again, chemicals have impregnated the outer cardboard housing of the "B" batteries so I am only going to salvage the Phenolic resin connector at the top. I used a pencil to mark a plus sign next to the positive terminal. It will make wiring the new batteries in the proper polarity much easier later. 

Here is the inside of a Burgess M30 "B" battery. Each circular black object is an individual 1.5 Volt cell that are wired in series to achieve 45 Volts DC. If you count them you will find 30 individual 1.5 Volt cells as 30 x 1.5 Volts = 45 Volts!

Change of Plans

Below is the damage that the chemicals that leaked out of the "A" battery did to the chassis of my Trav-Ler Model 5020 radio. I don't what to chance having the chemicals in the cardboard housing of the "A" and "B" batteries doing further damage, which is why I am abandoning everything but the top connectors.

Battery Box Construction

My new strategy is to create battery boxes out of 1/8 plywood I obtained from a local crafts store. The battery boxes will have the same dimensions as the "A" and "B" batteries they will be replacing. Below is a picture of the plywood after I marked out all of the pieces I require for the two "A" and two "B" battery boxes. I made sure that I left room between each piece for "kerf" or the width of the saw blade cut.  

Time to build the "A" and "B" battery boxes, I carefully sanded the edges of each plywood part with fine (200) grit sandpaper then dry fit the parts together. Once satisfied with the fit, I glued the pieces of the battery boxes together using Elmer's wood glue. I placed a piece a kitchen wax paper under the glued pieces so as to prevent the them from sticking to my work bench if some of the glue oozed out of the joints. Gluing the battery boxes together takes some patience, you cannot glue all of the pieces together at one time. I first glued the sides first then the top and bottom and finally glued reenforcement pieces in place as needed.

It is time to mount the battery connector at the top of the "A" battery boxes.  I use two small brass screws acquired from a local crafts store to hold the connector in place.

Time for fitment of the battery connector at the top of the "B" battery boxes.  Two small brass screws also hold this connector in place.

I choose to install three AA batteries in the "A" battery boxes to achieve the nominal 4.5 Volts DC required. I found two inexpensive 3 x 1.5 Volt AA battery holders on Amazon for a couple of dollars. The AA battery holders have an on/off switch protruding from the bottom side. I simply mounted the battery holder 1/16 inch off the bottom of the battery box to allow for clearance of the switch. The battery holder is fastened to the side of the battery box with two brass screws.

3X1.5 AA Battery Holders on Amazon

Mounting the 9 Volts batteries in the "B" battery box was a little more difficult. I decided to use the bottom and side of the battery box to hold the batteries in place. I then cut a 9 Volt metal battery clip in half to use as the third mount point. The tension of the "springy" 9 Volt metal clip does a good job of holding the 9 Volt batteries in place. Five 9 Volts batteries are required in each "B" battery box to achieve the 45 Volts DC. 

9 Volt Battery Clips on Amazon

Battery Box Finishing

Time to disassemble all part from the battery boxes and apply water based Polyurethane to them. I apply two coats of Polyurethane then sand with a fine grit (200) once dry. I then apply a final finishing coat. I use water based  Polyurethane because it is easy to clean the paint brush and wash off of my hands.  

Final Assembly

Time for final assembly of the "A" battery boxes. I soldered the wires from the AA battery holder to the battery connector. I wrote in pencil the proper polarity of the connector in an earlier step. 

Here is a picture of one of the completed "A" battery boxes.

It was easier to perform all the wiring of the "B" battery box outside of it. The five 9 Volt battery clips are wired positive to negative in a loop that extends to the terminals of the  battery connector.  I wrote in pencil the proper polarity of the connector in an earlier step. ​

Next, I mounted the battery connector, wiring, and 9 Volt Battery clip assembly to the "B" battery boxes. 

Here is a picture one of the completed "B" battery boxes.

Testing

Testing time, I connected the finished "A" and "B" battery boxes to my vintage 1947 Trav-Ler Model 5020 radio, then placed the power switch in the Battery position. Success! after a brief warmup I started to hear AM radio stations from the speaker.  

Notice how nice my "A" and "B" battery boxes fit in the battery slots of my vintage radio.

Here is a picture of my "A" and "B" battery boxes in place and ready for the back cover to be installed on my Trav-Ler radio.

oops, I still need to tuck the AC cord into the back of the radio, It is not needed as I will be running on it on battery power!

Here is video of my "A" and "B" battery boxes in action powering my Trav-Ler Model 5020 radio!