With the summer coming I thought it would probably be a good idea to do a bit of portable working on the top of a nearby hill. I wanted to build something with valves that would deliver a useful 10 watts or so and that could be used to contact the stations on the Saturday morning VMARS net. The receiver section I decided was probably best built with solid state components to save space and to allow everything to run off 12 v. The HT for the transmitter would be sourced from 3 smallish rotary transformers which I had lying around in the shack.

To give it a vintage feel I built the transceiver to fit in an old wooden microscope box. The transmitter consists of 5763 as a driver/oscillator from a standard crystal for the main AM frequency here in the UK which is 3615 kHz. The PA is a 5B/254M operated in class C and plate modulated by a pair of EL84’s. The HT supplied by the dynomotors is about 360v for the PA and 300v for the modulator with this I get about 10w carrier and about 20-30w PEP so not quite 100% mod!

Above you can see the separate compartments for the PA and the modulator.

The receiver is based on the RAT5 design by Dave GW4GTE which uses an AM chip the TDA1072A which is a complete single conversion receiver in a single package. The finished rig with it’s power supply is pictured below:

For those that are interested here’s the schematic