[Hallicrafters] Re: [Boatanchors] simple transmitter using the1625tube

[w7qho]

The 1625 and 807 are derivations of the 6L6 beam tetrode and as such do not have suppressor grids.  They do have a set of beam forming plates that are internally  connected to the cathodes, either inside the glass or in the bases of some examples as has been mentioned. Roughly equivalent  pentode types would be the 802, 837, RK-75, 2E22, 307A among others.  Pentodes can be suppressor grid modulated but beam power tubes cannot be successfully modulated by applying audio to the beam forming plates alone. 

I clearly remember the use of modified 1625s in GG amplifiers back in the 1950's.  837s were used in GG amps too but these tubes have half dissipation rating of the 1625s, which made performing surgery on the bases of certain brands worthwhile.  Don't remember ever reading just why this was necessary, i.e., just what happens if "ordinary" 1625s were used in these GG circuits (distortion, instability, what?)
--
Dennis D.  W7QHO
Glendale, CA
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