[Amps] more on 3-500Z uses [TSPA]

["John T. M. Lyles" <jtml@lanl.gov>]

The 4CW250,000Bs are used as DC coupled modulator, not an audio 
modulator. They are in parallel, not push pull, as they dissipate 
about 220 kW total in heat. They impose a linear control on the HV to 
the anode of the GG tube. The GG tube is driven hard into saturation 
(class B-C ish) so that the RF output linearly resonds to the 
modulation imposed. It is not linear amplification at all. Some 
people call this a totem pole amplifier, in that the modulators are 
in series with the HV from the power supply, and the RF tube is at 
the bottom of the totem, with the grid grounded. The RF drive comes 
into the filament of the tube, via a cavity structure.

Amplifier is pulsed so that it is only operating about 10% of the 
time, and this pulsing is also applied via the modulator, which 
switches off the HV to the final, and the Rf drive is also removed.
Power supply IS the size of a small show store. Actually the 
capacitor vault is.

The end result of all this is to drive linear accelerator cavities to 
accelerate protons.

PS, in a few years I am working to replace the modulators and GG 
amplifiers, and go to using a GG/GS tetrode final RF amp, which will 
be used as a linear amplifier alone. All modulation will then be 
applied at the milliwatt level in the predriver chain.

There are some more subtleties, in that the RF amplitude and phase 
are tightly controlled in real time. Hence the bandwidth of the big 
modulators is about 100 KHz.

73
John
K5PRO

> 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

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