[Amps] SB 220 Exploding Resistor

[Carl]

----- Original Message ----- 
From: "Jim Thomson" <jim.thom at telus.net>
To: <amps at 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 at cox.net>
> To: "'Tom Hellem'" <tom.hellem at gmail.com>, <Amps at 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