Command Receiver - Frequency Convertor

This is a handbuilt combined power supply and RF signal frequency changer to suit the R26 command receiver.
I have built it from oddment parts I had lying around.
The basic frequency coverage of the R26 command receiver is 3 to 6 MHz.
With a 2 MHz crystal in the convertor; tuning range will become 5MHz to 8 MHz.
With a 5 MHz crystal in the convertor; tuning range will become 8MHz to 11 MHz.
When using the convertor (to extend frequency coverage),
an external aerial is connected to the convertor,
and the "converted" o/p is fed into the receiver aerial terminal.
The set-up could now be described as a dual-conversion system, with the R26 acting as a "tuneable I.F."
The One tube HF converter 80/40 mtrs design, is from Bob W9RAS His Youtube video about it, is here




May 1966 pg 83 Electronics Australia magazine article (3 band S/W convertor)
describing the efficiency of a 6BL8 triode/pentode when used as an oscillator-mixer circuit.
Injection from oscillator anode to mixer grid seems to occur
because of stray capacitance between adjacent pin connections 1 & 2 inside valve!



Constructed using recycled componentry.
The power transformer(s) I've used had a 32 volt and 140 volt secondary windings.
The 6BL8 filament current of 450 mA is the same as the command receiver filament drain (@ 24V)
Therefore I connected the two in series and fed from the 32 volt tfmr winding.
Works OK, and obviates the need for another 6.3 V winding just to supply the 6BL8 heater!
The 140 volt is full-wave rectified/filtered to give 225 volt DC B+ voltage.
Power switch:
STBY warms up the filaments,
REC gives B+ to the receiver,
CONV' gives B+ to receiver and convertor.