Tio Pedro wrote:
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


Early SSB exciters used the 7360 tube as a mixer / vfo so I know this
type of tube will work as a self excited converter. As far as pulling
is concerned this would depend on the difference between the oscillator
and IF frequencies, or the oscillator and signal frequencies. But
pulling shouldn't be any worse than with the pentode mixers that
couplied the oscillator to the same grid as the signal input. At least
the 7360 isolates the signal and oscillator to different electrodes.
Also the signal input is balanced and shielded by the screen grid.
OTHO I don't know how good (stable) an oscillator this tube is.
Probably better as a crystal oscillator than a vfo.