This item has exposed high voltage underneath the chassis. The radio you receive will look very similar to the photos. The large tuning dials may vary, depending on what I have in stock. Also, the old brass 1920's variable capacitors are becoming difficult to find, so you may receive a radio with gray plates, in lieu of the pictured brass. Whatever the case I promise it will have the old world nostalgic appearance.
The circuit has a battery powered dc to ac inverter, and the no load dc voltage underneath the hood is over 340 volts! So even though the power source comes from harmless low voltage batteries it can still be lethal if not handled responsibly. This is a vacuum tube ham radio QRP cw transmitter and regen radio.
The circuit uses a 12SN7 twinplex circuit for the regenerative receiver and a 12A6GT pentode tube for the cw transmitter. The 12A6 transmitter tube requires only 0.15 amps drain from the power source and since a 12L6, 12V6 or 12W6 tube requires considerably more amps for the filament and will produce maybe a 10% max gain in power out, I decided to just go with the 12A6 tube for this radio to converse battery power drain.
So while you can get slightly more power out with a 12V6 tube for transmit, the constant battery drain for the filament is more than 200ma greater than required for a 12A6. The inverter, which powers only the transmitter tube, turns off instantly when switched to receive mode. So it is not working at all when in the regenerative receive mode. The chassis requires an external 12 volt power source. I like to use a small motorcycle or golf cart battery, but so much the better if you have an old car battery that you are not using.
This powers the filaments and inverter when in transmit mode. On the chassis a 9 volt rechargeable battery is required for the receiver, which is connected in series with the incoming 12 volt source, providing about 20 volts or so to run the regen detector. The receiver requires high impedance 2 to 4k ohm inductive or piezo headphones, NOT INCLUDED in this listing. You may use a well filtered 12 volt bench supply to run this radio.
It should be capable of at least 3 amps in transmit mode (regulated dc). For this circuit there's only a few ma drain on the 9 volt battery, so it will go for many hours if not days before needing to be recharged.The QRP transmitter output on 40 meters is about 2.4 to 2.5 watts. Power out on these old audio tubes drops off considerably as you go up in frequency. On another listing I have this radio in a multi-band version, and power out for 160 and 80 meters is in the 3 to 4 watt range. For this listing you will receive one plug-in coil and one QRP HC49 crystal for 40 meter cw, mounted in a FT-243 style holder. Frequencies available are 7030, 7040, 7055, 7110 and 7118 khz.
Please let me know if you have a preference. The dc inverter circuit employs a pair of TIP41C power transistors, working with a 6-0-6 volt 5 watt transformer that has a secondary winding of 220 volts. The output is then rectified by a 1N4007 diode, then filtered, for about 340 volts dc, no load.I will include a hand-sketched wiring diagram of this item, plus a sketch of all control panel functions. The controls are receiver main tuning, fine tuning, receive antenna coupling and regenerative action/power on/off switch. The transmitter has a single control for power out, with link coupling to the antenna. There's a single send/receive switch which controls all necessary functions, including high voltage power on for transmit and switching the antenna. So you only need a single antenna for send/receive.
In send mode the audio output will automatically be muted. AGAIN, EVEN THOUGH POWERED BY BATTERIES, IT CAN BE QUITE LETHAL IF NOT HANDLED WITH RESPECT! This is a given for most any ham radio transmitter.
Schematics are available for most of my radios, which you can find on my other listings.