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[Amps] A general question about why anodes get hot

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Subject: [Amps] A general question about why anodes get hot
From: i4jmy@iol.it (Maurizio Panicara)
Date: Wed, 18 Sep 2002 20:20:36 +0200
>
> Tube-type amplifiers dissipate roughly half as much heat as the amount of
> RF they produce.

In my experience with broadcast FM transmitters, solid state mosfet
amplifier are not so much better than a tube PA plate efficiency already
when the device is alone, I mean a single pushpull unit.
Actually a 300W mosfet module is better in terms of efficiency if compared
with the equivalent level vacuum, but as the power is increased the story
becomes different with solid state.
A number of modules and coulpers (typically wilkinsons if one doesn't want
to see often all the mosfets dead in case of failure) are required to obtain
large power and, as well extra modules are added some extra loss arise and
in spite of (claimed) "super efficient" switching PS and super efficient PA.
The claimed broadband units (untuned) are a compromise and the solid state
PA effiiciency may vary (decrease) noticeably varying the frequency.
When lab measures are taken seriously, beyond a certain power the real
overall efficiency of a solid state PA is not different than a tube
amplifier.
Not rarely I mesured is worst.

73,
Mauri I4JMY

> -  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
> www.vcnet.com/measures.
> end
>
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