[Amps] SB 220 Exploding Resistor

George at6c at bellsouth.net
Tue Jan 19 10:33:34 EST 2016


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 at jeremy.qozzy.com>
>> To: "Tom Hellem" <tom.hellem at gmail.com>, <Amps at 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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