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December 16th 05, 05:09 AM posted to rec.radio.amateur.homebrew

On 15 Dec 2005 20:20:15 -0800, wrote:

A Tetrode
may be a good way to go, but I wonder if a 4146 driving into something
else might be a bit cheeper. Maybe a pair of 813s? As I said the 1965
ARRL handbook claims a kw out with a pair of 813s,but I have my doubts.
They are cheep enough - $55 ea at tubesandmore.com The Taylor 572B
can be had for about 200 bucks for 4 of em. Would this be a viable
option?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(I assume you meant 6146 in the above)

Remember, adding a driver stage complicates the design because you
will have to add bandswitching to the driver too, unless you can
figure out a way to broadband a tube amp, something not easily done.
If you grid-drive the 6146 you will have to add neutralizing as well.

A pair of 813s have only 250 watts plate dissipation. Getting 1kw out
of them is pushing it and their life will be short. For just a bit
more you can get a single 3-500Z and have twice the plate dissipation.
This is still not the best way to go, IMO. If you are really stuck at
the ten watt drive level, the class AB1 tetrode passive grid solution
would be the best approach.

Big, strong amplifiers are not cheap. Don't scrimp or you'll be sorry.
Are you aware a 1500 watt rated bandswitch will cost about as much as
a PAIR of 3-500Zs? And that's only the beginning. Plate transformer,
power diodes, filter capacitors, tune and load capacitors, chassis and
cabinet, blower, on and on.

Homebrewing a high power amp is a prestigious accomplishment, but in
terms of overall cost, buying commercial is cheaper in the long run.
The money you spend on a homebrew amp will likely never be recovered.
A commercial amp can retain a large percentage of it's price when the
time comes to sell. In fact, if you buy a quality used one you might
well be able to use it for years and sell it for more than you paid.
Something to keep in mind.

My wallet hurts just thinking about it. :-)

73, Bill W6WRT

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