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

["kenw2dtc" <kenw2dtc@comcast.net>]

Thank you for the explanation.  I jumped to conclusions thinking 'audio 
modulation' and was puzzled by tube line up.  That's a serious rig John. 
Again thanks.
73,
Ken W2DTC
----------------------------------


----- Original Message ----- 
From: "John T. M. Lyles" <jtml@lanl.gov>
To: "kenw2dtc" <kenw2dtc@comcast.net>; <amps@contesting.com>
Sent: Tuesday, February 01, 2005 2:36 PM
Subject: more on 3-500Z uses [TSPA]


> 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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