Date: Mon, 18 Jan 2016 14:13:10 -0700
From: John Lyles <jtml@losalamos.com>
To: amps@contesting.com
Subject: [Amps] SB 220 Exploding Resistor
Message-ID: <569D5566.3090503@losalamos.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
If you get a strong enough wirewound resistor, this can suffice as the
surge current limiting resistor for a spark over in a tube. With 250
amps at the beginning of the overcurrent (2500 V/10 ohms) spike, there
is enough magnetic field to break a wirewound R as the windings have
mechanical force between turns. I have always used bulk carbon for
series R, like Kanthal Globar makes. They are exactly the right part for
this.
http://www.globar.com/ec/bulk-ceramic-resistors/globar-bulk-ceramic-non-inductive-resistor-applications.html
http://www.globar.com/ec/bulk-ceramic-resistors/axial-leaded-resistors.html
Finding them through distribution might be a problem, though. Has anyone
else used these?
John
K5PRO
## The energy absorbing types are the AS series. The SP series is what
is used in dummy loads, etc.
I have used these real small globars back in the 70s... for the parasitic
suppressor in several amps, but
I don’t remember if they were type AS or SP. Dunno if Globar will
sell you just 1-2 of them ?
SP types are rated for 350 deg C.
AS types are good for 250 deg C
## There is no issue using wire wounds for a glitch R.... provided they
are sized correctly.
2500 /10 ohms = 250A.
3000 / 10 ohms = 300A
## 2500 / 50 ohms = 50A
3000 / 50 ohms = 60A
## A single 50 ohm @ 50 watt WW works quite well..and does not
implode. However, I use a HV
fuse in series with the 50 ohm glitch Resistor..... to interupt the peak
fault current...asap.
## I have also tried paralleled 100 ohm @ 50/100 watt wirewounds.
## Ameritron sells the globar type AS glitch resistor.... forget the
value they use. If its real low, like
10-15-20-25 ohms, you could always series 2-5 of them. But I believe
they are not cheap. I believe
they only sell one value.
## I have also tried the bigger, tubular type SP resistors for a glitch
R, and they work good. But these were obtained
surplus. I have also tried large tubular type AS, and they work very
well.
## But the wire wounds are cheap to buy new, and in any value and wattage
you want. Readily available.
50 ohms will limit fault current to a low value.... and is not high enough
to cause heat issues, when used on
high duty cycle modes. Also, the V drop across 50 ohms, with 500-1000
ma of plate current is not an issue either.
## You will not implode a 50 ohm @ 50 /100 watt WW any time soon.
## surplus globars show up on the market from time to time..and also
work good.
I bought several 50 ohm, 90 watt CCS type SP globars, same as used in
a heath dummy load, these also work
excellent for glitch use. I believe ameritron also sellls em.
Jim VE7RF