[Amps] Re: more on 3-500Z uses [TSPA]
kenw2dtc
kenw2dtc at comcast.net
Tue Feb 1 15:05:41 EST 2005
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 at lanl.gov>
To: "kenw2dtc" <kenw2dtc at comcast.net>; <amps at 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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