> 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
> 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.
The 813 is one of my favorites even if the 4-400's just look nicer <:-))
The 813's were my second amp project, right after the 6C21 back in the
old days. Speaking of IM and old tech. When I put the second 6C21 on
(after vaporizing the plate in the first) a ham about 4 doors down and
across the street called and asked what I was running. Guess it durn
near blew his receiver off the desk as I was only about 5 KHz above him
on 40. Although less power, the 813 amp was much cleaner. Much cleaner
on the air and construction too.<:-)) Of course my first transmitter was
a pair of 6L6's build up on the corner of an old TV chassis. I used the
power supply from the TV. Man that thing was big and ugly for 75 watts.
> 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.
I have a number of those cabinets I might use some day... As well as
several SX101 incarnations, and several (3 I think HT-32 incarnations
that I might rebuild some day.
> 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.
Yup, the sub chassis is a great idea and it also makes the construction
easier as the builder can tackle one part of the project at a time. I've
never seen a large project yet that couldn't be broken down into steps.
> The above just skimmed the subject but its easy to see that complicated and
> budget busting isnt a requirement.
Some good points.
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