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

To: "kenw2dtc" <kenw2dtc@comcast.net>, amps@contesting.com
Subject: [Amps] more on 3-500Z uses [TSPA]
From: "John T. M. Lyles" <jtml@lanl.gov>
Date: Tue, 1 Feb 2005 12:36:01 -0700
List-post: <mailto:amps@contesting.com>
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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