[Boatanchors] regeneration and selectivity

[Drew P.]

Henry wrote:

"I brought up this idea a couple of years ago on one of the WS19 reflectors. About 30 years ago I added adjustable regeneration in the (first?) IF stage of a TCS and a Bendix RB-(?) aircraft receiver by running a high resistance rheostat between the grid and plate in series with a blocking cap.
It was very effective in both receivers, resulting in Q multiplier-like selectivty."



I have seen a somewhat similar scheme used in the Hallicrafters S-120 which
is a minimalist general coverage receiver. The tube lineup in this unit 
is the miniature tube "All American 4" - the 35W4 being replaced by 
selenium and a power resistor. The unit's 12BA6 I.F. amplifier stage's 
suppressor grid is connected to chassis ground via a pot and nothing more. The pot is the front panel control labelled "BFO".  Increasing this 
control's resistance initially provides regeneration; further advancing the 
control causes the I.F. stage to oscillate, providing a BFO function of sorts.

Drew