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 wi
ll 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.
Sent from AOL Mobile Mail
-----Original Message-----
From: Jim W7RY <jimw7ry@gmail.com>
To: Jim Thomson <jim.thom@telus.net>; amps <amps@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@contesting.com";>amps@contesting.com</a>
Subject: [Amps] Glitch resistor + fuse?
Date: Wed, 15 Nov 2017 09:49:54 -0600
From: "Doug Renwick" <<a href="mailto:ve5ra@sasktel.net";>ve5ra@sasktel.net</a>>
To: <<a href="mailto:amps@contesting.com";>amps@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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