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G6Tanuki · 9th Oct 2019, 4:50 pm

The circuit with the anode-cathode capacitor makes more sense.

I also remember seeing a 50MHz-converter circuit in a 1950s US handbook which used the pentode of the ECF82 as an electron-coupled Colpitts xtal oscillator, extracting the 3rd harmonic of the xtal from a tuned-circuit in the anode of the pentode, then feeding this at high-level to the grid of the triode; RF input (preamplified by a common-cathode-connected 6AK5) was fed to the triode cathode in a circuit that looked at first rather like the classic cascode RF-amp, the oscillator drive to the triode was said to be so high that it basically operated as a switch rather than a traditional mixer so it had good mixing-linearity when faced with high adjacent signal-levels (US 50MHz hams have big issues with crossmodulation due to loads of TV stations in their equivalent of "Band 1").

9th Oct 2019, 4:50 pm	#14
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: ECF82 frequency changer The circuit with the anode-cathode capacitor makes more sense. I also remember seeing a 50MHz-converter circuit in a 1950s US handbook which used the pentode of the ECF82 as an electron-coupled Colpitts xtal oscillator, extracting the 3rd harmonic of the xtal from a tuned-circuit in the anode of the pentode, then feeding this at high-level to the grid of the triode; RF input (preamplified by a common-cathode-connected 6AK5) was fed to the triode cathode in a circuit that looked at first rather like the classic cascode RF-amp, the oscillator drive to the triode was said to be so high that it basically operated as a switch rather than a traditional mixer so it had good mixing-linearity when faced with high adjacent signal-levels (US 50MHz hams have big issues with crossmodulation due to loads of TV stations in their equivalent of "Band 1").