Hi All,
Carl & Bob offer some sage advice herein to the newbie amplifier builder...!
Neophytes, take heed...
My own personal "route to redemption" in this regard went thusly:
(A) I started out building the 4x811A design featured in the ARRL's SSB
manual;
(B) I learned (the HARD way!) the importance of MATCHING tubes in such
multi-tube designs;
(C) I settled on using just a PAIR of 811As (my surplus supply ran out!);
(D) I elevated the power level by replacing the 811As with a pair of 572Bs,
and finally,
(E) Years of struggling with the above after-thoughts compelled me to dream
about my "ultimate" kilowatt---cheap tubes, ALL bands, tuned input,
removeable plate tuning cap, inductive tuning (as required), etc.---and so I
built a pair of 813s in parallel grounded-grid in 1990...and I continue to
use this outfit to this day.
Anyone with a backlog of the old "HAM RADIO" magazine could do no better
than to carefully read the 3 part series on HB linears written by the
venerable Bill Orr (W6SAI), which appeared in the late 1970's. It is surely
MUST reading for anyone & everyone contemplating taking the "homebrew
plunge" and rolling one's own...
~73~ de Eddy VE3CUI - VE3XZ
**********************************
----- Original Message -----
From: "Carl" <km1h@jeremy.mv.com>
To: "Robert Briggs" <vk3zl@bigpond.com>; <amps@contesting.com>
Sent: Saturday, January 30, 2010 9:08 AM
Subject: Re: [Amps] Good amp to buy maybe build..
> 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
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|