----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Tuesday, January 19, 2016 2:50 AM
Subject: [Amps] SB 220 Exploding Resistor
Date: Sun, 17 Jan 2016 19:48:16 -0600
From: "Dale LeStourgeon" <dlestourgeon@cox.net>
To: "'Tom Hellem'" <tom.hellem@gmail.com>, <Amps@contesting.com>
Subject: Re: [Amps] SB 220 Exploding Resistor
Tom, go to Harbach and buy a pack of their .82ohm resistors 2W ( $6).
Your
resistor did its job as it acts like a fuse in case there is a tube or
other
b+ short. Many amps used something like this. I had this issue with my L4B
recently when a tube failed. Glad Harbach has the resistors since
otherwise there are hard to find.
73
Dale K5AJZ
## No, the glitch resistor is not there to explode, nor is it intended to
be a HV fuse.
The glitch resistor is there to LIMIT the FAULT current to a safe value.
The function
of the HV fuse..( or a .82 ohm 1/2 watt carbon comp resistor) is to
INTERRUPT the
fault current.
## 3000 / 50 ohm @ 50 watt ww resistor = 60 A peak fault current.
The HV fuse
will blow open in a split second. You need both items.
## RL drake used a .82 ohm 1/2 watt CC resistor, in series with the
B+...used as a fuse.
Local store had loads of em, so stock piled years ago. A 2 watt is a bit
too big imo.
## The BUSS HVU series of HV fuses will open off in < 2 msecs.
## A 25 ohm @ 25 watt WW will also work as a glitch resistor, but
fault current will
be double. 3 kv / 25 ohms = 120 A. If a 50 ohm @ 50 watt wont fit,
another option is to
use TWO 25 ohm @ 25 watt in series. They can be miles apart, as long
as they are wired in series.
Jim VE7RF
Dentron used a pair of 1 Ohm 1/2W carbon comp in parallel as a fuse at the
base of the plate choke and it was useless for an arc. They did blow when
572B's went in a run away oscillation and melted the glass.
A film resistor will self destruct a lot faster; I just replace with a
regular glitch type..
Ameritron went with the type mentioned by John Lyles in their big amps, kind
of expensive, and of questionable use over a vitreous enamel type. Prior to
that they used nothing .......from zero to overkill IMO.
Carl
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|