[Hallicrafters] HA-1 keyer

[k2wh at optonline.net]

Thanks to all on the explanation and I should have known it is possible.  The comparison of a typical NE-2 bulb in a relaxation oscillator circuit is a very good analogy.

As a matter of fact, the side tone in the HA-1 uses a NE-2 in a relaxation oscillator.  So, the answer was right under my nose.

P.S.  I have (2) of the HA-1 keyers.  They both work fine.

K2WH