[BC] FM Grounded Grid Triodes & FM Tetrodes

[Dave Hultsman]

You are corrrect early tetrode stages had touchy neutralization or they could become squirrley.
That is why Lloyd Winter at Collins and Eimac engineers came up with the grounded screen idea which elimated the screen capacitors. In the early tetrode stages the screen bypass capacitors were distributed around the base of the screen ring on the tube socket. They were prone to mechanical failure at the screw base.  Usually when that would happen the neutralization would change.  I have heard many of the ITA's and Collins' built by ITA,  arc over and blow the rest of the capacitors usually when I was  trying to retune to get rid of the spurious.  Of course later on, one of my favorite higher powered transmitters would ocassionally get squirrley and burn up the entire tube shelf and socket.
 
In a message dated 11/11/2010 9:32:34 A.M. Central Standard Time, mark3xy at gmail.com writes:
>I quickly learned to be careful when tuning the ITA, otherwise it
>would go into "spread spectrum" mode with spurs every 350 kHz across
>most of the educational band.  I'll have to say the 3CX series used by
>CCA was a much more stable approach to grounded grid.

>Mark