[AMPS] More on the SB220

[Jon Ogden]

>Checked out the SB-220 this morning for damage. The only component that blew
>was the 0.82 ohm resistor. I noticed that the resistor is of the metal film
>type with a 2W rating, manufactured by Phillips. Heath manual calls for a
>wirewound resistor rated at 2W.  When the original big blow happened last
>year, I had replaced Harbach's .82 ohm 3W WW with the 2W metal film type. Is
>this significant?

Don't know why a 2W wirewound would have more dissipation capability than 
a 2W metal film.  I'd put in a bigger wattage value anyhow if that's what 
keeps blowing.

>
>In all the years that I spent working on high power transmitters, I have
>never witnessed a failure caused by a parasitic when the transmitter was
>powered but unkeyed. That's why I'm having a hard time accepting that the
>fault was caused by a parasitic. But, of course, that's not to say that its
>not possible.

Agreed.  Everything bad that happens in amplifiers is not due solely to 
parasitics.  I belive this is NOT your problem, but rather that it sounds 
like you just might need a higher wattage resistor.

73,

Jon
KE9NA


--------------------------------------------------------------------------
Jon Ogden

jono@enteract.com
www.qsl.net/ke9na

"A life lived in fear is a life half lived."


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