[HBR] Re: Another receiver project

[Bill Higgs]

Waltah and the group,

I was noting with interest the HBR-4, and also noting with interest the late W1KLK's design in Feb '72 QST (an experimental receiver for 75-meter DX work, p. 41). Doug used a low-gain RF stage with a grounded grid dual triode . . . the RF stage used dual tunable Cohn filters, so the point was only to make up the loss in the filters, about 5-6 dB. He used a 7044 "computer" tube; your beloved 6J6 might well work here also. Interesting; should be stable in grounded grid mode. Mixer is the venerable 7360, driven unbalanced by a series-tuned 6U8A VFO/buffer.

The design of the BFO is of interest, as it looks as though it might be modified a bit for push-pull output by using the buffer (tetrode) stage of the 6U8A as a phase splitter, replacing the RFC with a resistor and taking outputs from the plate and cathode. Probably would reduce the output by half, but you'd get it back in absolute voltage difference at the deflection plates. Dunno if you've biased the deflection plates in your mixer or not (the 7360 requires 25V or so bias, the 6JH8 allegedly does not) . . . I don't know if biasing the plates positive affects the overall conversion gain of these tubes. My NEXT project after the HBR-??(WAY ahead of myself here) will be a project using the 6JH8 as a mixer and a pair of 6EH7 frame grid tubes in the IF; probably for 20 meters with another 6EH7 as an RF stage.

Doug's IF is 455Kc with a Collins filter, followed by a Q Multiplier stage set up for notch mode. The rest of the set is fairly conventional.

Work on the HBR-?? is going to be suspended for several weeks, pending the relocation of my shop. The termites finally won.

Bill Higgs, NT4C