[Amps] Glitch resistor + fuse?

[gudguyham at aol.com]

I doubt that.  I want to emphasize that the " special "  resistor we are speaking of is NOT a garden variety carbon composition resistor.  It doesn't necessarily explode but it will crack and break in pieces.  It has the ability to take a surge and once it dampens the surge it may open depending on the severity of the surge.  Obviously it is meant to be sacrificial like a fuse is.  Drake used it in the L4/7 power supply B+ and Heathkit used it in the B- and doubled as the grid shunt resistor.  For the class and B+ voltages in these amps, this special resistor is sufficient protection. Many add additional gizmos as well but I believe this resistor will be the one that handles the job if left in circuit.  Larger amps need additional protection once B+ goes much over what these amps  have.  Unknowing hams who don't realize that Heath used this special resistor as the grid shunt needlessly add additional gizmos.  Bottom line is they don't hurt but this grid shunt resistor/fuse will probably be the limiting factor anyway which eliminates the need of anything else.  It's too late to undo all the fallacies created by the Internet.

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-----Original Message-----
From: Jim W7RY <jimw7ry at gmail.com>
To: Jim Thomson <jim.thom at telus.net>; amps <amps at contesting.com>
Sent: Wed, Nov 15, 2017 11:14 PM
Subject: Re: [Amps] Glitch resistor + fuse?


I'm pretty sure they are .82 Ohms at 2 watts. There are lots of them on EBay 
for free shipping and small quantities.

73
Jim W7RY


-----Original Message----- 
From: Jim Thomson
Sent: Wednesday, November 15, 2017 1:15 PM
To: <a href="mailto:amps at contesting.com">amps at contesting.com</a>
Subject: [Amps] Glitch resistor + fuse?

Date: Wed, 15 Nov 2017 09:49:54 -0600
From: "Doug Renwick" <<a href="mailto:ve5ra at sasktel.net">ve5ra at sasktel.net</a>>
To: <<a href="mailto:amps at contesting.com">amps at contesting.com</a>>
Subject: [Amps]  Glitch resistor + fuse?


<The Tentec Titan amp uses a single 10 ohm 25watt ohmite.

<Doug

##  with say 1.5 A of plate current, that amounts to 22.5 watts diss, so it 
will work ok.
But 10 ohms doesnt limit the fault current to a low value.  2600 divided by 
10 = 260 A fault current,
which is still a bunch.   2600  divided by 50 ohms = 52 A fault 
current..which is a lot less obviously.
Anything is better than nothing of course.

##  Forgot to mention in my previous posts, re protection diodes.  I use 
several 6A10 s in parallel, to
make one big diode.   3 or 4 of the 6A10s, each with a 400A  surge rating, 
albeit only for 8.3 msecs,
is then good for  1200-1600A.   With out any HV fuse in there to interurpt 
the fault current, it can take
a while for the breaker in the 240 vac line  to open up.   The HV filter C, 
plus the value of the glitch Resistor,
form a simple  RC network.

##  eg.  25uf  and  10 ohms  =  .00025 secs.   = .25 msec
25 uf and 50 ohms =  .00125 secs     = 1.25 msecs
100 uf  and  50 ohms =  .005 secs     = 5 msecs

## and thats just the time it takes to partially discharge the filter cap 
down to just 36.8 % of the original B+ voltage.

Jim  VE7RF
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