[Amps] SB 220 Exploding Resistor

[Carl]

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 at bellsouth.net>
To: <amps at 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 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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