When I do the math I get different numbers. At the 66% plate
efficiency that is often quoted as typical for class B linear
operation,
which frankly isn't pie-in-the-sky considering that 50% of the drive
power feeds through to the antenna, the slide rule says that it will
take 1212 watts input to get 800 watts output. That's 312 watts
dissipated -- only a paper thin margin above the ratings.
Don't even talk about class C where 80% efficiency would
mean that the tube dissipates 200 watts.
----- Original Message -----
From: "Joe Subich, K4IK" <k4ik@subich.com>
To: <n8de@thepoint.net>; "'Amps Reflector'" <amps@contesting.com>
Sent: Wednesday, December 01, 2004 8:56 PM
Subject: RE: [Amps] Dx pedition amp ???
>
>
> N8DE writes:
>
> > IF you can find one, the Dentron MLA-1200 fits your needs
> > quite nicely at 800 w CW output using a single 8875 tube
> > and a separate power supply with total weight of about 45
> > pounds [most of the weight is in the PS].
>
> At 800 Watts CW output, you are seriously abusing that tube.
> The 8875 is rated for 300 watts plate dissipation, 800 W CW
> even in class C would be almost 400 watts of dissipation.
> Considering that the 8875 is difficult to find, and very
> expensive if available, I would not push it nearly that hard.
>
> The MLA-1200 does not include any kind of grid trip circuit
> to protect against over drive ... a real problem with a grid
> rated for 5 watts! Further, the amplifier lacks a tuned
> input which could represent additional problems for many
> current transceivers.
>
> Further, the MLA-1200 does not include 160 meters - a serious
> shortfall for a Dxpedition amplifier.
>
> 73,
>
> ... Joe, K4IK
>
>
>
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