[AMPS] Help building mono band amp

[Mike Baker]

Hello,
    Get an ARRL handbook from say, 1965.  For several years there was an
article on building monoband KW amps using a pair of 813's.  I used these
articles as the basis for my very first amp in 1969.  813's are still
available via various sources including the internet and are quite
inexpensive.  I scrounged around for a year or so on e-bay and made a deal
with a fellow to buy 9 tubes and 4 sockets for $80 including the shipping.
7 tubes were carbon plates (the best ones IMHO) and 2 were the metal plates.
One broke in shipping (not carbon,no loss).  For any band up to 20 meters
they kick butt and love high voltage.  The book specs say 2500VDC max for
the plates but up to 3500VDC is commonly used in GG linear service.  4 tubes
will give you a comfortable KW out at 2.5 to 3KV.  For up to say 750 out you
could use two tubes and have an easier time finding the filament
transformer.  (10VAC at 10Amps for two tubes)  Used a surplus 150pf cap for
my tuning on 40M and made the coil out of copper tubing.  The power xfmr was
a surplus unit that ran 900VAC at 1A as a voltage doubler.
    Total cost back then (1969) was maybe $30 but you could still build one
today for less than a $100 with a little patience and scrounging. The best
part of building is you get to test and refine a bunch of talents.  Sheet
metal fabrication, wiring or harness making, parts recognition and purchase,
electronic design, metal finishing/painting, etc. just to name a few.
    A few caveat come to mind.  I mention these to anyone who is
contemplating building their first amp.
    1.    HIGH VOLTAGE is not just a sticker on the side of a cabinet.  It
is a seductive lover that will KILL you and bring you to room temperature if
not respected and the rules of working around it obeyed to the letter.  You
seldom get a second chance let alone a third to violate the rules.  I have
been blessed with having survived lethal shocks twice and figure that a
third is not likely so be aware.
    DO NOT put your hands inside a cabinet that has High Voltage (anything
above 24Volts AC or DC) present.  The AC power mains kill more people every
year than any other type of electrocution.
    Work with one hand in your pocket. NOT leaning on a grounded metal
cabinet or desk.
    Always disconnect the mains power and flag or wrap up the plug end so it
isn't accidentally reconnected by someone else.  (The old story about two
guys working on a transmitter together and as one guy has his hands inside
the cabinet, the other finds the plug pulled from the mains and plugs it
back in without thinking, saying something like, "OH, I found the problem,
it isn't plugged in; try it NOW!"  Room temperature.
    Use a "shorting" stick or discharge stick.  In days of old a large metal
loop shaped like a large fish hook with a wooden handle and a piece of braid
with and alligator clip on one end clipped to ground.  Today I would modify
that to be a probe type of stick with a non-conductive handle hooked to a
long string of 2 watt metal film resistors with a total value of about 100K
Ohms or so. Use it to check the discharged state of the HV caps before you
start working on the amp.
    Use a shorting clip across the HV to GND and remove it when you are
done.  IF, IF someone accidentally turns on the power while you are inside
the cabinet, it will/should blow the FUSE or Circuit Breakers and keep you
from being a dead fish.
    NEVER, NEVER build an amp without proper fusing of the mains.
    NEVER, NEVER bridge the safety devices (fuses or breakers).  They have a
purpose.
    NEVER, NEVER work on a project involving High Voltage while you are
exhausted or overly tired.  Falling asleep into your work can be deadly.
Too tired and you do stupid things you might never recover from.
    NEVER, NEVER work on a project involving High Voltage if you are
intoxicated.  Same result as the previous warning.  Save the 807's for the
celebration of a successful days work.
    All of these previous warnings are old hat and inevitable truths to
staying alive while working around High Voltage as I am sure most would
agree.  Let me add a couple of my own.
    Realizing that the Human nature of things is to do something as long as
you can so long as it doesn't hurt you, all of us at some time or another
have violated one of the rules listed above.  Some of us have survived the
experience.  Some of us had Help surviving the experience.
    If you don't know CPR go and learn it.  Once you do you will posses a
skill that you may never have to use (hopefully).  But the alternative to
not knowing it may cost someone their life and it just might be someone you
love.  My personal feeling is that it should be taught in junior high school
and a requirement for a drivers license. It could greatly reduce the risk of
death to thousands.  Remember, electrocution causes the heart to stop and
CPR applied immediately after the victim is clear of the danger can make the
difference in being back to normal or a "gomer".
    If you must work on a piece of equipment that involves high voltage do
NOT do it alone.  Be sure someone knows where you are and what you are
doing. Have a buddy give you a hand. (It can be more fun doing these things
as a "buddy" project.) There is nothing more unnerving than to have your
wife come home and find you "well done" and at room temperature out in your
garage or in your shack.  It ruins their day and yours!

    OK, I know this all seems like I am describing the obvious, but it is
worth repeating.
    It is sort of like meeting a beautiful woman in a club.  YOU ONLY GET
ONE CHANCE TO MAKE A GOOD FIRST IMPRESSION!  You will seldom get a second
chance.

    Good luck with your amp project.  READ, READ, READ, and if you still
have questions, at least you know where to ask.  In spite of all of the
banter and sniping at each other on occasion, this is still one of the best
resources for information on AMPS.  You could never say this group isn't
passionate about what they are doing.
    Again, good luck.
Mike Baker  K7DD
k7dd@qwest.net
----- Original Message -----
From: "Jean-Michel Bombar" <jmbombar@graphnet.fr>
To: <amps@contesting.com>
Sent: Wednesday, October 10, 2001 12:57 AM
Subject: [AMPS] Help building mono band amp


>
> Hello,
>
> I would like to built my first HF amp, I am thinking of a 1Kw mono band
amp
> for the 40M band.
> Does any of you have any idea of where I could gather informations to
start
> this project?
>
> Thanks.
>
> Jean-Michel, F5MMX
>
>
> --
> FAQ on WWW:               http://www.contesting.com/FAQ/amps
> Submissions:              amps@contesting.com
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> Problems:                 owner-amps@contesting.com
>
>


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