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?
In response to queries by members of the group, yes, I had already made Rich
Measures 110V bias mod.
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.
I must say that mods I have done have at least prevented widespread damage.
I'll see what the answers are regarding the resistor before I decide on
making some radical changes.
Walter - VE3EN
Walter Fairclough
wfairclo@netcom.ca
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