[Amps] Glitch resistor

[Jim Thomson]

Date: Sun, 13 Nov 2016 01:52:21 +0000 (UTC)
From: Dick NY1E <dick at ny1e.com>
To: "amps at contesting.com" <amps at contesting.com>
Subject: [Amps] Glitch resistor

My SB220 stopped operating, with no plate current and pegging the grid meter after a bright light out of the rear fan grill. It seems an added glitch resistor opened, 10 ohm 10 watts doesn't seem big enough. did it do its job and sacrifice itself? The resistor looks fine no burns or anything. Should it be bigger or keep this size as a fuse?de Dick NY1E

##  Your glitch is not big enough.  Use a  50 ohm  /  50 watt  wire wound.  Your existing glitch resistor has gone open.   With no B+ present, and drive applied,  you will indeed peg the grid meter in any GG amp..and with just a few watts of drive.  
The electrons are now all attracted to the grid....instead of the anode...hence pegging the grid meter.  

##  for a real HV  B+ fuse, use either a single super fine strand of wire, taut between  2 x standoffs..... or a .82 ohm,  1/2 watt cc resistor.  

##  You can also wire in a simple grid current fuse.   Install a rear mount 3agc fuse holder, and use something like a  200-250 ma FAST rated 3agc fuse.  Wire the grid fuse between chassis and cold end of the oem grid meter shunt resistor.

##  next time you experience an event / glitch /burp/ etc,  the 50 ohm /50 watt ww  will LIMIT the fault current to a safe value.  3200 / 50 =  64 A fault current.   The B+ fuse will open off asap, with 64A flowing through it. 

##  with no B+ present, and full bore drive applied, the grid fuse will open up.   With grid fuse open, you no longer have any path for DC grid current.  Input swr rises to infinity...and xcvr shuts itself down. 
If B+ is present, and  grid fuse opens up for whatever reason, PO  drops to zero, and input swr rises to infinity.  Xcvr high swr protection kicks in asap, and PO of xcvr drops to nothing. 

##  3agc rear mount fuse takes a few seconds to replace.  The  50 ohm /50 watt  ww will never burn open. The hb  B+  fuse will require top cover removal to replace.   Wire any B+ fuse  before the glitch and not after it. Both are in series.

##  If you want it bomb proof,  you can also install a 2nd  HV fuse, between plate xfmr sec..and FWD.    In series with one leg , either leg, of xfmr sec. 

Jim  VE7RF