RadioBanter - View Single Post - QUESTION: Fun with Svetlanas or Staying alive with kV power supplies

July 14th 05, 02:29 AM

On Wed, 13 Jul 2005 wrote:

Date: 13 Jul 2005 14:05:17 -0700
From:
Newsgroups: rec.radio.amateur.homebrew
Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power supplies

My knowledge of vacuum tubes and kV power supplies is limited. I have
been reading an article in the ARRL Handbook detailing the construction
of a 1kW HF Linear. I'd like to try my hand at building something like
this. I found the article a little intimidating: Ceramic insulators,
parasitic suppressors, thermal and mechanical engineering etc. Is
there some book that details this type of thing with an explanation of
the whys as well as the whats and hows. My priorities a

1) Safety. I'd like to be alive to make my first 1kW QSO
2) Avoiding equipment destruction, arc overs, black smoke, explosions
etc
3) Safetly troubleshooting this kind of equipment, loading testing
etc.
4) How to deal with tubes: warm up, care, etc...
5) Avoiding TVI (ITV), parasitic oscillations etc.
6) Longevity and Duty Cycle issues etc.
7) Costs and sources.

Hope someone can help.

Thanks,

Tim

When I was a kid, I was building 10kV HV transformers, 100kV Tesla coils,
spark coils, discharging HV capacitors that make "bangs" about as loud as
medium sized firecrackers, smoked resistors, shorting outputs on 100 amp
transformers just to see the sparks fly, etc., and so I have an intuitive
feeling for various stuff. I've gotten shocks maybe a dozen or two times
in my life. Nasty. Most of the time these were from a finger to thumb and
not through my heart. When current was involved, I'd get a button of
burned flesh on my skin and that really hurts plus burnt flesh really
stinks like almost nothing else except dead flesh that has been dead long
enough at room temperatures to really stink. RF burns...you don't
feel the pain (which also really hurts) until after the burn and you get
that burnt flesh stink, too. Even from 50 watt rigs they can be bad.

My experience includes mechanical devices, electric drills, bolts and
nuts, threaders, chassis punches, electric drills, band saws for cutting
metal sheets, etc.

If you have never done anything "hands on" in your life, then your grand
plan dream may be an undertaking that you would be wise to avoid. On the
other hand, if you are mechanically inclined and practical and NOT a klutz
(definitely not a klutz), then I'd suggest starting with a smaller
and easier project and then move up.

At points where you start working with lethal voltages and currents, you
do need to be careful. Very very careful. They say when the power is on
and the cabinet is open, you need to keep one hand in one of your pockets.
Stand on a piece of dry wood at least 1/2" thick, etc. Yes, arcs and smoke
can be intimidating. Just the surprise from an arc can make you jump in an
unpredictable way and if not hurt yourself from the electrical shock, then
you'll bang your head or something else.

Parasitic oscillations and TVI: At least start with a KW level dummy load
and know what the book says about neutralization and how to test for it
and adjust it. Also, you cannot have enough meters to measure everything.
Even filament voltage and current. I'd have a meter for every circuit:
plate, screen grid, control grid, cathode current, and voltages on all of
them.

Weirdest discoveries: serious RF noise from solid-state diodes. Also,
serious RF noise from HV transformers (output connected to
absolutely nothing, but AC on primary and can hear the noise across the
SW band). Weirdest lightning effect: blew out a very big (1 kW) plate
transformer (2200-0-2200 v) and bypass capacitors to ground and nothing
else in the hamshack was affected (collins S line, Drake twins, ten tec
rig, etc.).

Key warning: know what you can and can't get away with using HV silicon
diodes.

Building your own gear: I have had no sense of pride, accomplishment, and
usefulness like building my own. Especially from junk in the junk box. My
biggest rigs were 500 watt linears using 4-400As, and a few others. Built
kits (Knight, Heath [too bad they are not around any more]), too.

W4PON