An introduction:
I found a box full of old radio valves when cleaning my house under coming Christmas. I desided to make a valve receiver. Some of tubes were brand new. I had european types like ECL83, ECL84, ECL82, EH90, ECH83, EF95, some 6BE6 tubes, 5MHz xtals and a big tuning capacitor with three sections.
Bases:
In a PA unit I used a line transformer. A separate main supply gave about +80V anode voltage and 6V heating voltage. I made all connections without printed circuits like in old radios. I haven't done a RF state yet, but I do it later. Power line resistances and capacitors are big ones to handle enough power and high voltages. My chassis was a thin folded copper plate, a bad one but enough for the first experiment.
Coils:
A wire in all coils is about 0,3mm thin. L2 and L4 are toroids. I had white toroids but I think violets might be better. L3 has been salvaged from an old radio and made new windings, primary 40 turns and secondary 8 turns on a 5mm body. L1 was from same old radio. L1 = 40 turns, tapped 8 turns from ground, 7,5mm body L2 = 20 turns, inductance about 27uH, toroid L3 = 40 turns primary, 8 turns secondary, 5mm body L4 = 16 turns, 3 twisted wires, the first wire's end to the second wire's begining...
BFO:
You might need to change a BFO frecuency. Increase a serial inductance or capacitance or change 47pF and 150pF capacitancies. My version seems to work without modifications.
Tuning:
Find good limits to VFO with TR1 and Cx. I use first a trimmer in a place of Cx, measured it and repaced with a solid capacitor. A Vfo range is 8.5MHz - 8.8MHz, so a receiving range is 3.5MHz - 3.8MHz. Connect an antenna, a trimmer to Cy's place and find a good signal strength in both ends of frequencies, repeat this several times. Measure Cy and replace with a solid capacitor.
Future developments:
A better body for this radio with a power supply on it and a box for it. A RF state for example with EF95, AGC, DDS tuning and maybe a valve transmitter.
Olavi Parkka OH6KWV
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