[MrFixr55]

Hi Bridkarl,

Though having lived in Suburban Long Island NY my entire life, farm sets always interested me, as these radios were often a "lifeline" between the rural farmer and civilization. I have several farm sets made between 1936 and 1940, some using the 2V tubes that were first introduced in 1932, others using the octal and miniature 1.4V tubes. Farm sets using the 2V tubes required a 2V storage battery that was brought to town to charge, plus the disposable B batteries. Other farm sets were designed similar to automobile radios to run off a 6V storage battery. A vibrator type B power supply provided B+ voltage similar to car radios. The farmer either swapped the battery between the home and car (or other farm implement, had a windmill "Win-Charger", a 6V power plant or took the battery to town to have it charged. Still other farms had a 32V power plant consisting of a generator that ran by day and a bank of batteries to run the home at night. Radios were designed and built to run on 32VDC also, using low-B+ "space charge" tubes.

For sets that ran on batteries, the farm family used them sparingly due to the expense of running the radio.

Farm radios like yours and portable radios using the Sylvania-designed 1.4V octal tubes became quite popular starting in 1938. Usually, the circuits were rather similar between these "farm" sets and the battery-operated (only, no line power option) portables of the time. Power usually came from a 1.5V (A), 90V (B) battery pack, or 1.5V A battery and 2 45V B batteries in series, depending on make and model. I would think that yours ran from a battery pack.
I have several sets using these tubes including an RCA 14BT2 farm set, and BF Goodrich - Mantola 419, Bulova 220 and "Trav-ler" (model unknown) Battery operated portables. These last 2 use the newer 7 pin miniature tubes. I also have several battery-electric portables including a 1947 Zenith 8G005 Trans-Oceanic and the AM only version 6G001, and the radically newer and lighter 1948 4G800 "Zenette".

I don't play mine for long periods of time, so I use an alkaline D cell for the filaments (A battery) and either 10 9V batteries or my ARBE III for the 90V B supply. I did get a Silvertone "Power Shifter" battery eliminator that I will install in the RCA. These were rather popular, because as rural areas received electric power, the farm owner did not really want to discard the battery set that they paid good money for, and certainly wanted to stop buying batteries.

Unlike the earlier farm sets using 2V tubes which may have used push-pull output, these sets don't require a C battery. Grid bias for the audio section was derived by putting a resistor between the negative terminal of the B battery and B- (chassis ground).

Unless attacked by mice or other vermin, and unless wired with rubber insulated wire, these sets are rather easy to fix, as almost no heat was generated in these sets. All tubes are easily available on eBuy. The non-electrolytic caps and resistors are likely good, but caps should be replaced anyway. It seems strange that electrolytic filter caps exist in sets that are battery powered, but replace them. The radio is unstable without them.

Unfortunately, the schematic does not identify what color power leads go to what. However, as the schematic shows:
A- goes directly to chassis ground.
B- goes to the junction between R17 and R18
B+ goes through the switch to the junction of C22, the output transformer (20) and B+ distribution.
A+ goes through the switch to the filaments of the 4 tubes.

The only downside of these sets other than the need to power them, is the fact that the output power is about 10-20% of the output power of the common AA5 set and fidelity suffers. However, sensitivity is similar to AC-DC AA5 sets.