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Tuesday, 5 June 2012

6C4 valves

At FDIM 2012 / Dayton HamVention I picked up a dozen 6C4 triode valves.
A conversation with a few including Hans Summers G0UPL who has been most helpful and the suggestion is a superhet receiver, for 80 and 20m. The front end band-pass filter determines 20m or 80m, all you need is to switch that front end filter, to select which band. No problem, 2 bands :-)

One possible line-up to aim for might be built from these modules, each could practically be built and tested on its own:

1. Switched Bandpass filters for 20m and 80m. I have some interesting variable capacitors that will make these a little special.
2. RF amplifier (V1), typical triode RF Amp.
3. Dual-triode mixer - Google "Pullen mixer" (V2, V3) plus oscillator input from:
4. Franklin VFO at 5.0-5.5MHz (V4, V5) W2LYH QST, October 1961. Hans recent low drift VFO using dual valves is inspirational. I have an old Mecanno worm drive that I will investigate.
5. 9MHz tuned circuit - perhaps something like a T50-6 and a trimmer capacitor. A secondary winding to match impedance to the crystal filter
6. 9MHz G-QRP club CW filter (I have the SSB one too)
7. Two IF amplifier stages (V6, V7)
8. "Infinite impedance detector" as per G3VA book (V8) + oscillator input from:
9. BFO, single valve crystal oscillator - There are multiple options Pierce, Colpitts usually work nicely too (V9)
10. AF amplifier (V10)

I will also try to make a TX.

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