Farm Radio Power Supply, 1.5v & 90 volt B+. Line power.

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Up for auction are new FarmPS-1power supplies for Farm radios which use 1.5volt battery and aB-battery of 90volts. This power supply is isolated and regulated to allow constant use with 4, 5 or 6 tube battery powered radios. These radios, very often for sale in this category, typically have a tube line up of a 1A7, 1N5, 1H5 and a 1A5 or equivalent output audio pentode. The earliest reference I can find for these tubes is in my 1938 Sylvania Tube manual. They show a battery radio with this exact line-up. The 1C5, with later tubes 1Q5 and 3Q5, was a popular output pentode, putting about 200 milli-watts into a speaker. Not really loud but nice for a table top or bed-side sized radio. Sibley's "Tube Lore" shows that these tubes were registered in June 1938. This power supply will also work for newer radios with the 7-pin miniature tube line-up, like the portable superhet shown in the RCA receiving tube manual RC-15. That radio uses a 1R5, 1T4, 1U5 and 3S4 tube line-up.Radio history buffs will note that the original, i.e. "true," farm radios use 32 volts and 6 volts. The 32 volt value was a popular "wincharger" supply, while the 6 volts allowed running your radio from the tractor parked next to the house, during an overnight battery charge from the wind. This power supply is only for the 1.5v battery tubes meant to operate from dry cells. While the open circuit voltage of a 90v dry cell pack is close to 90v, it is closer to 84v after a short load time (60 cells at 1.4v). Below about 1.1v on the filaments the filaments on these tubes don't have much emission.To protect your tubes, this supply has over-voltage and over-current protection, as well as voltage regulation on both the plate supply and the filament supply. T is a blinking red LED to let you know that the supply is turned on. As shipped, you can simply supply an IEC standard grounded line cord, or remove the IEC receptacle and add a switched 2-wire lamp cord-- available at your local home improvement store.This version being sold is a partial-kit. The board has been assembled as shown in the photo, but is not supplied with the line filter (ferrite beads are installed instead), line cord or alligator clips for connection to the radio. You will have to provide your own connections. As shown, the line power input takes a standard IEC power cord (like a computer) and the outputs are screw terminal blocks, which accept stranded or solid wires. The units are fully functional and will be calibrated as described in manual. We did a new revision of the board and these are left over from the first production. The opening asking bid is less than our purchased parts cost.You will have to have some electronics experience to properly utilize this power supply, as it requires proper connection to your radio and careful attention to the dangerous voltages present. However if you are comfortable working on tube radios, then you will find this easy to use. I suggest that you first read the manual which can be seen at: /PDF_files/farm_man.pdf (this is the manual for the fully complete version, but the details still apply) and study the schematic at: /PDF_files/farmps_kit.pdf before bidding. The kit .pdf gives the schematic and complete parts list showing Mouser and Digi-Key catalog numbers. Note that all the parts have already been assembled to the board and professionally flow soldered. You just add the line cord and connection to your radio. You will have to get the manual and partslist from the web site, as they will not be with the package.A wonderful resource for getting information on your radio is . You can find details on your radio as provided by Riders from this site. These boards will be shipped for $5.00 via priority mail to USA destinations. Note that this power supply runs from 120V 60Hz only, North American line voltage, so I would advise against overseas bidders. We generally ship on Thursday or Friday. Paypal is the best way to pay.Thank you for your ... read more

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