Hi Carl,
Your right I looked up the momentary overload and it is only 1.5 times
the rated power.
73, George
W2GS
On 1/20/2016 4:49 PM, Carl wrote:
And how well does it hand a surge manybe 10X its rating?
Not very well I'll guarantee
Carl
KM1H
----- Original Message ----- From: "George" <at6c@bellsouth.net>
To: <amps@contesting.com>
Sent: Tuesday, January 19, 2016 10:33 AM
Subject: Re: [Amps] SB 220 Exploding Resistor
John,
Have you ever looked at Surface Mount Power Film Resistors? A 25
ohm/ 25 watt is available from Mouser at around $6. I used one of
these as the input resistor on a tetrode amp several years ago and it
has work without any issues.
http://www.mouser.com/ds/2/62/MP725-2439.pdf
73, George
W2GS
On 1/18/2016 3:13 PM, John Lyles wrote:
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
Date: Sun, 17 Jan 2016 13:19:20 -0500
From: "Carl" <km1h@jeremy.qozzy.com>
To: "Tom Hellem" <tom.hellem@gmail.com>, <Amps@contesting.com>
That blown resistor may have been underated and blew during a tube
arc. The
idea of a surge suppressor is to not fail and allow the
milliseconds for a
fuse/breaker to open.
A 10-15 Ohm 20-25W Real wirewound resistor will cure that problem.
Look for
Vitreous Enamel in the description.
Carl
KM1H
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