[Amps] 3-500Z uses [TSPA]

[kenw2dtc]

K5PRO wrote:
"My coworkers and I maintain some five 'sockets' for 3-400Z at work, each 
used as an inverter/driver for a 4CX3000A which screen modulates a pair of 
4CW250,000B which are plate modulators for a Burle 7835 grounded grid 
triode."

Awesome.  Are the 4CW250,000B's really plate modulators or is it the stage 
where the actual modulation takes place?  It makes me think of modulation 
transformers and modulation reactors the size of a small shoe store.  As 
soon as you mentioned that the Burle is grounded grid it makes me think that 
the Burle stage is a linear amp rather than a stage to be plate modulated. 
Please add a little more information and straighten me out.
Thanks and 73,
Ken W2DTC