wrote:
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

I built a homebrew KW about 15 years ago using a pair of 4-400 in
grounded grid. It worked fine on 80-20 but I never did get the tank
Q adjusted well enough for good output above that. Not that it couldn't
have been done with a bit more tinkering.

The power supply put out about 4000 volts no load. I used a time delay
circuit with a relay and a power resistor to limit the in-rush current
while the capacitor filter bank charged. It had a relay whose ac coil
was across the primary of the plate transformer that shorted out a power
resistor in series with the primary. As the caps charged and the input
current fell so did the voltage drop across the power resistor until the
primary voltage rose to the relay's pull in voltage shorting out the
resistor. (Idea from ARRL HB).

A second time delay circuit did the same thing for the filaments of the
4-400's. This relay also locked out a second relay that applied power
to the plate transformer. Result, the plate supply couldn't be turned
on until the 4-400 filaments were warm, that delay was about 1-2 seconds
during which a power resistor in the filament transformer primary
limited the 4-400 filaments to half voltage.

The filter caps were 10 330uf 450v computer grade units in series, each
cap bridged by a 50k 25W power resistor to even the voltage across the
caps and act as a bleeder resistor. A 1ma meter with a suitable
multiplier resistor in series served as a voltmeter across the
capacitors (I forget how many meg ohm it was). The meter case was
thick enough plastic to be insulated enough from the chassis (and
and besides the main plumbing was behind several meg ohms). The meter
read 5000v full scale.

I always assumed there was voltage across the caps when I worked on the
rig. First pull the plug(s). Wait till the voltmeter drops to zero.
THEN put a heavy screwdriver with a well insulated handle from ground
to the HV terminal to be sure! (I used to do that to picture tubes
when working on tv sets). Keep on hand in the pocket if you need to
adjust anything when it's hot. BTW an RF burn can be more deadly than
a DC jolt. (Think microwave oven).

HV isn't the only thing that can get you. High current can give you
a nasty surprise. Like the guy replacing some batteries on a golf cart.
He was using a ratchet wrench to tighten the battery clamps and he
ended on the most positive battery terminal. The handle of the wrench
hit the chassis of the golf cart putting it between 36 volts and ground
of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench
glow WHITE HOT? (and melt?)

Ken Scharf wrote:
The filter caps were 10 330uf 450v computer grade units in series, each

Probably dumb (and WAY off topic) question:

What's the *intended* purpose of a 450v "computer grade" capacitor?

--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Doug Smith W9WI wrote:

Ken Scharf wrote:
The filter caps were 10 330uf 450v computer grade units in series, each

Probably dumb (and WAY off topic) question:

What's the *intended* purpose of a 450v "computer grade" capacitor?

--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com


They were used on the input side of large switching supplies for
minicomputers, and some later mainframes. I pulled about 100 of them
from the multiple switching supplies in an Amdal mainframe about 10 or
12 years ago.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

What's the *intended* purpose of a 450v "computer grade" capacitor?
====================
Switch mode power suppplies ??


Frank GM0CSZ / KN6WH

"Highland Ham" ) writes:
What's the *intended* purpose of a 450v "computer grade" capacitor?
====================
Switch mode power suppplies ??


Frank GM0CSZ / KN6WH


I thought "computer grade" was either a marketing name, or at the
very most defined a certain design of capacitor.

In other words, they weren't designed for computers, but saw a lot of
use in them. They weren't cheap electrolytics of the type you'd
see in the average consumer equipment of thirty years ago.

You'd see them promoted in the surplus ads, and the ones I remember
were metal-cased, and had screw terminals for connections. I still
have one around I bought at a hamfest for a 12V power supply. It
was about 10,000uF (which was a fairly large size capacitor circa
1973 or so), had a voltage rating of about 16volts, and was the size
of a can of coke. Obviously a lot more impressive than the average
electrolytic of the day.

So once you had that style, it wasn't whether they were used in
computers or not, so of course you could have high voltage "computer
grade" capacitors.

I have no idea if it was a marketing ploy, "hey those are used in
computers [which were still uncommon at the time, and usually big
and very expensive], they must be good capacitors", or if there
was something about their design that made them better than the
average electrolytic of the time.

Michael VE2BVW

In article ,
Ken Scharf wrote:

I always assumed there was voltage across the caps when I worked on the
rig. First pull the plug(s). Wait till the voltmeter drops to zero.

A trick, courtesy of Bob Pease: whenever you build a power supply
circuit which carries line voltage or higher, stick an NE-2 neon bulb
and a suitable dropping resistor across the caps, and place the bulb
where it's clearly visible when the case is opened.

If the bulb is lit (at all) the caps have enough voltage in them to
give you a nasty bite.

THEN put a heavy screwdriver with a well insulated handle from ground
to the HV terminal to be sure!

I've heard cautionary notes about this... if you do this prematurely,
the arc can be scary (and dangerous in some cases - "arc flash" burns
can be severe) and I believe it's possible to damage or wreck some
caps as a side effect of a catastrophic high-current discharge.

A heavy grounding wire, with alligator clips, and with a
current-limiting resistor is another possible solution. You want a
low enough impedance to drain away any charge which may come out of
the cap's dielectric "soakage", but high enough to avoid a dangerous
arc flash when you first hook it up.


Keep on hand in the pocket if you need to
adjust anything when it's hot.

That's one of the best single pieces of advice around! Also, be aware
of what sort of grounded metal is around your workbench. Doesn't help
much to keep one hand in your pocket, if you lean your belly against a
grounded metal bench!


HV isn't the only thing that can get you. High current can give you
a nasty surprise. Like the guy replacing some batteries on a golf cart.
He was using a ratchet wrench to tighten the battery clamps and he
ended on the most positive battery terminal. The handle of the wrench
hit the chassis of the golf cart putting it between 36 volts and ground
of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench
glow WHITE HOT? (and melt?)

Haven't seen that myself, but I've heard of people who have had
screwdrivers, etc. literally vaporized under such circumstances.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:
In article ,
Ken Scharf wrote:
snip
HV isn't the only thing that can get you. High current can give you
a nasty surprise. Like the guy replacing some batteries on a golf cart.
He was using a ratchet wrench to tighten the battery clamps and he
ended on the most positive battery terminal. The handle of the wrench
hit the chassis of the golf cart putting it between 36 volts and ground
of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench
glow WHITE HOT? (and melt?)


Haven't seen that myself, but I've heard of people who have had
screwdrivers, etc. literally vaporized under such circumstances.

My brother came home from a business trip once with a scar on his wrist
5/8 inches wide and all the way around -- the truck was having
electrical problems & he shorted his metal watch band through the 12V
battery (there was a wrench involved in there somehow, of course).

I felt for him, but I was very glad that _he_ was the one to learn this
first hand, rather than me...

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

On Thu, 14 Jul 2005 11:32:47 -0700, Tim Wescott wrote:
Dave Platt wrote:
In article ,
Ken Scharf wrote:
snip
HV isn't the only thing that can get you. High current can give you
a nasty surprise. Like the guy replacing some batteries on a golf cart.
He was using a ratchet wrench to tighten the battery clamps and he
ended on the most positive battery terminal. The handle of the wrench
hit the chassis of the golf cart putting it between 36 volts and ground
of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench
glow WHITE HOT? (and melt?)


Haven't seen that myself, but I've heard of people who have had
screwdrivers, etc. literally vaporized under such circumstances.

My brother came home from a business trip once with a scar on his wrist
5/8 inches wide and all the way around -- the truck was having
electrical problems & he shorted his metal watch band through the 12V
battery (there was a wrench involved in there somehow, of course).

I felt for him, but I was very glad that _he_ was the one to learn this
first hand, rather than me...

My dad (the first W3DHJ) told me a similar story.

It was in the late 20's. He was working on _his_ dad's Ford utility
truck. (Grandpa owned a dairy in Big Bear, Calif.) Six volts here.
The truck was parked in the driveway -- just outside the garage.
When my dad caught his ring between the positive terminal and the truck
frame, my Grandpa picked him up bodily -- ran him over to the rain barrel
at the corner of the garage -- and stuffed my dad's entire left arm (and
much of his upper torso) into the barrel.

( *The worst* thing you could do in a situation like that is try to _pull_
the ring off.)

My dad was a 90-day wonder in WW II. He then spent 25+ years in the
U.S. Army Corps of Engineers (we traveled the planet....) Most of his
duty assignments were as Post Engineer -- with the added responsibity
as Post Safety Officer. I always knew him to be evangelically anal
about safety. I'm sure that incident with the old Ford truck had a
wee bit to do with it.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
Pueblo, Colorado | @ | Jonesy | OS/2 __
38.24N 104.55W | config.com | DM78rf | SK

On Thu, 14 Jul 2005, Tim Wescott wrote:

Date: Thu, 14 Jul 2005 11:32:47 -0700
From: Tim Wescott
Newsgroups: rec.radio.amateur.homebrew
Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power
supplies

Dave Platt wrote:
In article ,
Ken Scharf wrote:
snip
HV isn't the only thing that can get you. High current can give you
a nasty surprise. Like the guy replacing some batteries on a golf cart.
He was using a ratchet wrench to tighten the battery clamps and he
ended on the most positive battery terminal. The handle of the wrench hit
the chassis of the golf cart putting it between 36 volts and ground
of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench
glow WHITE HOT? (and melt?)


Haven't seen that myself, but I've heard of people who have had
screwdrivers, etc. literally vaporized under such circumstances.

My brother came home from a business trip once with a scar on his wrist 5/8
inches wide and all the way around -- the truck was having electrical
problems & he shorted his metal watch band through the 12V battery (there was
a wrench involved in there somehow, of course).

I felt for him, but I was very glad that _he_ was the one to learn this first
hand, rather than me...

I've got a related story to tell: I saw many years ago two guys try to
jump start another guy in the winter time. I only saw a few seconds and
surmised the following. These guys must have used the jumper cables to
connect the two twelve volt batteries in series, not parallel. Why? The
jumper cables were, themselves, literally smoking and not just a little
bit. Figure 24 volt power at, what, something like 500 amps(?) split
between heating up the interior of the two batteries and those jumper
cables (that are usually like #4 or #6 gauge?). How many seconds would it
take for on the order of 5000 watts to cause jumper cables to get up to
200-300+ degrees Farenheit? Those guys scrambled to tear those cables off
the batteries and I could tell by how they were handling the cable that it
had to be hot. They could have warped the lead plates.


--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Dave Platt wrote:
In article ,
Ken Scharf wrote:

HV isn't the only thing that can get you. High current can give you
a nasty surprise. Like the guy replacing some batteries on a golf cart.
He was using a ratchet wrench to tighten the battery clamps and he
ended on the most positive battery terminal. The handle of the wrench
hit the chassis of the golf cart putting it between 36 volts and ground
of some VERY HEAVY DUTY batteries. Ever see a Sears ratchet wrench
glow WHITE HOT? (and melt?)

Haven't seen that myself, but I've heard of people who have had
screwdrivers, etc. literally vaporized under such circumstances.

The canonical "Take-Your-Rings-Off" reminder in our electronics shop
in Japan, back when I was in the AF, was a color image, taken at our
base hospital, of a finger burnt to the bone all the way around: one of
the techs had got his wedding ring between ground and a high-current
low-voltage supply.

--
Mike Andrews W5EGO 5WPM
Extra
Tired old sysadmin working on his code speed