Ameritron/MFJ sells a Globar they use for a glitch in their "senior" amps.
Overpriced and uneeded IMO at those power levels. A plasma isnt going to
even get started before the fuse blows anyway...this aint a 250KW
application!
Carl
KM1H
----- Original Message -----
From: "John Lyles" <jtml@losalamos.com>
To: <amps@contesting.com>
Sent: Wednesday, April 17, 2013 4:24 PM
Subject: [Amps] HV Resistor Source
The "industry standard" for such a resistor is a pulse rated R like a
Kanthal Globar. The company has changed names a lot recently, so search
for them. These are carborundum bulk resistors, non inductive. You can
live with inductance of a WW, of course, but in a dead short, you might
find your resistor flashing over with plasma. Then it isn't such a good
resistor. Globar isn't cheap, but they are excellent in this application,
as well as for dummy loads. You have to study their literature, type AS
and SP material. One is better for continuous dissipation and the other is
best for very high peak voltages but low dissipation. They make them with
clip in connectors or wires.
73
John
K5PRO
Message: 8
Date: Wed, 17 Apr 2013 00:58:47 -0500
From: donroden@hiwaay.net
To: Amps@contesting.com
Subject: Re: [Amps] HV resistor source
Message-ID: <20130417005847.27844mn5ynlr261j@webmail.hiwaay.net>
Content-Type: text/plain; charset=ISO-8859-1; DelSp="Yes";
format="flowed"
Quoting Jim Garland <4cx250b@miamioh.edu>:
> That's going to be quite a resistor, inasmuch as 4KV across a 30 ohm
> resistor amounts to a half million watts of dissipation! A 4KV pulse
> 50uS
> wide, once per second, would dissipate 25W.
> 73,
> Jim W8ZR
The resistor isn't to ground..... it's in series with the tube(s) that
may draw 1 amp intermittently ... therefore 1 amp squared through 30
ohms is 30 watts.
If the tube draws more amps ... a short or a bad load... maybe a two
amp spike... that is 120 watts which will hopefully burn out the
resistor
( acting like a fuse ) before the transformer or diode stack goes up in
smoke.
Don W4DNR
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