For the amp builder with little or no experience start off simple. Dont
waste money on expensive and fragile tubes such as the 8877 at this stage.
Stay away from apparent bargains in Class C designed Russian military
surplus that have been hyped by sellers for SSB use only to dump on the
unsuspecting; IMD is in the range of some of the worse US 50-60's
technology.
Contrary to an opinion or two there is nothing wrong with GG versions of the
813 and 4-400A. IMD is in the mid -30's if you quit trying to get super
power out of a pair. Go for 700-750W from 2 x 813 and 1000-1200W from 2 x
4-400A. Up to 4 x 813's can be used and they can be mounted horizontal in
similar alignment as 572B's and 811A's. They are dirt cheap as well as
sockets, easy to cool and very tolerant of mistuning. The fancy protective
circuitry is a line fuse.
At those voltages (2000-2500) and power, air variables are fine as are the
common hamfest/fleabay ceramic bandswitches which are easily reconfigurable
in many cases.
Start the metal by mocking up dimensions to figure what is needed. The PS
can be included or seperate depending on the size of the iron you scrounge.
Cheap cabinets are all over hamfests and Fleabay. Be it a generic Bud style,
from an old Hallicrafters RX/TX/Amp or 50-60's HP test equipment. Or have a
local sheet metal house bend up a clamshell style as used in most commercial
amps. Hint: make the base from steel and the top aluminum if the tank
circuit will be close to any metal.
Stay away from a full size chassis if possible as it wastes a lot of space.
Hammond has a wide range of chassis and prices are reasonable especially for
smaller sizes. READ a lot. Check out how all the commercial outfuts stuff
everything together and you will find its far more efficient and cost
effective than any ARRL or other ham published amp. Those tend to be mostly
ego builders to see how cute and complicated the authors can make it.
The above just skimmed the subject but its easy to see that complicated and
budget busting isnt a requirement.
Carl
KM1H
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