One of the very first Czech radio sets, made 1954. It belongs to the, so called, "0th generation" of the Czech public service radios. This piece was made for The Czech energetic company, České Budějovice, Southern Bohemia. The set is in excellent state, so far not tested, but looks very promising to work flawlessly.
The radio runs from 1,5V filament battery and 120V anode battery. The concept is an simple anode modulated transmitter (3L31), excited by multiplier chain and crystal oscillator (2x1F33, 3L31). Multiplication factor is 6, thus, the quartz frequency is somewhere about 13MHz. At reception, the XO and multipliers remain running, but the crystal is switched - to the second one of frequency, different of 76kHz exactly. After multiplication, there is a first heterodyne frequency for IF of 456kHz available at the end of exciter. For now, the PA tube works as a mixer (anode voltage deep lowered), there is no RF input amplifier, only three stage IF (3x1F33). AF amplifier works both as a modulator and as an RX AF - single 3L31 does it all. Very interesting is the mechanically modified standard relay for crystal switching. Full schematic diagram is available for swap at an email request. Thanks to OK3ZM for additional info.
Maybe inspiration?
Prototype of Amos as exhibited at Leipziger Frühjahrmesse 1958
