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Self-excited Beam Deflection mixers?? Opinions???
Still mulling over some RX design changes for a HBR receiver project that I
am considering building. It is going to be an updated version of the HBR receiver projects that W6TC, Ted Crosby, penned for QST in the late 50s and early 60s. I've decided to go with 6EH7 semi-remote pentodes for the RF and IF stages (overload resistant), meaning my filament current requirements are going out of sight.. 4.7 amps so far, so I want to cut back on the number of stages. To cut my tube count and heater energy, I'm looking for opinions on using 6JH8s with self excited injection. The 2nd mixer requires 1515kc injection, and I'm considering using the 6JH8 as a self-excited crystal oscillator to eliminate using a separate oscillator stage. Original plan was either a 6BH6 oscillator, or 6U8 combined osc/buffer. Second branstorm is to use a self-excited 6JH8 for the Product Detector and 85kc BFO, eliminating a separate tube and buffer stage that I had originally planned on using (another 6U8). Will osc. pulling be a problem? Any other drawbacks? First mixer will be a 6ES8 Pullen, with a 6U8 used for the tunable LO and buffer isolation. AGC will be via a 12AU7 plate detector, 12AU7 infinite impedance AM detector, 12AX7 Q-multiplier, 12AU7 first AFA and S-meter amp, and a 6AK6 AFA. First IF is 1600kc using cascaded modified ARC-5 IF transformers. 2nd IF is 85kc, using cascaded R-23 command RX IFTs. Pete |
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