On Thu, 18 Mar 1999 10:31:43 -0500 "Walter Fairclough"
<wfairclo@netcom.ca> writes:
>
>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.
Are you sure that one or more of the bias diodes did not short? That is a
common failure mode.
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?
I prefer a 2 or 3W metal oxide which can handle momentary overloads
without opening and taking out the multimeter if it is on "Grid" at the
time of failure.
>
>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.
Only in dreams where the SB-220 is concerned Walter.
73 Carl KM1H
>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
>
>
>--
>FAQ on WWW: http://www.contesting.com/ampfaq.html
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>Search: http://www.contesting.com/km9p/search.htm
>
>
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|