RM-29-* Remote Control Unit Repro BA-27 Battery

[SGM (ret.)]

So, another project that I've been working on to go with my SCR-610 radio set display is the RM-29 Remote Control Unit.  The RM-29 is a device that was plugged into the radio's microphone and earphone jacks (normally using PL-68 and PL-55 plugs on the TS-13 Handset).  The TS-13 handset was then plugged into the RM-29 and the field phone wire (W-100-A or -B) was then connected to the line terminals.  At the other end of the field phone wire was usually an EE-8 Field Phone (although other phones could be used, too).  This set up allowed the operator on the EE-8 Field Phone to communicate over the radio set.

The RM-29 had a three-position toggle switch that had radio, through, and phone modes.  In the phone mode and connected to a field phone, the RM-29 functioned exactly like any other field phone (ringer crank and all).  Unfortunately, unlike the EE-8 Field Phone which uses two common d-cell batteries, the RM-29 used a special (-)4-1/2V battery, BA-27.  Harumph!

In order to make my RM-29 work, I needed a 4-1/2V power supply.  After some research, I discovered a few photos of a vintage BA-27 sold during an online auction some time ago.  I was also able to determine the external dimensions of the BA-27.  Armed with this info, I decided to make a couple of repro BA-27 batteries that would run my RM-29 (in the phone mode).  Two would give me one for the unit and one for display.  As I refined my plans, I decided to make the repro battery box with a bottom that would open and close like a normal cardboard box and allow me to replace the commercial dry-cell batteries needed to add power.

So, here are my efforts.  First photo is of the original vintage BA-27, the other photos are of my repro batteries (installed in my RM-29, showing the removable dry-cell batteries, and finally, three shots of the three different voltages provided at each terminal - as per the original).  The repro batteries work perfectly, and I was gratified that my RM-29 in phone mode works as well as my EE-8 Field Phones with totally clear coms. 

I am considering making more of these to offer up to other collectors who want to use their RM-29-* Remote Control Units with other field phones.  If anyone here is interested in this, shoot me a PM/DM here and I'll fill you in on the details.  (I don't want to violate the forum rules and turn this thread into some sort of "For Sale" thing.  Nuff' said on that.)