[AMPS] Re: Parasitics

Tom Rauch w8ji.tom@MCIONE.com
Wed, 13 May 1998 23:23:33 +0000

> Date:          Wed, 13 May 1998 16:07:51 -0400
> From:          Pete Smith <n4zr@contesting.com>
> Subject:       Re: [AMPS] Re: Parasitics
> To:            amps@contesting.com

> At 11:40 AM 5/13/98 -0800, Rich Measures wrote:
> >Underloading will not cause a Tune-C arc in my SB-220 or TL-922.  The 
> >breakdown potential of a SB-220 Tune-C is c. 3600v, and for the TL-922,  
> >c. 5900v. 

and N4ZR Pete replied:
> I have repeatably (not repeatedly, or at least not very often) demonstrated
> tune-C arcing in my SB-220 in the SSB position.  It's an earlier unit, with
> the narrower-spaced tune-C. In all cases, the arcing happened as a result
> of underloading, or antenna selection error.  I have never experienced
> arcing when the right antenna was connected and the loading was set just
> past maximum output.  The amplifier is well-constructed and stock except
> for the Harbach metering/bias board and KM1H's parasitic suppressors.
> The same errors also produced arcing in a TL-922 I used years ago at 4U1WB,
> but I can't swear that it was the Tune cap, because you can't see into a
> TL-922 as well as an SB-220. The amp ran fine throughout an entire WPX CW
> once I worked out the procedural issues, with never a wiggle.

Rich claimed a K5 had parasitics in his 922 because "mistuning and 
misloading can not cause excess tank voltage or arcs. The K5 showed up 
and correct Rich, and said the nichrome Rich sent him was never 
installed. It turned out the cause of the arc was a bad gas discharge 
tube in his lightning arrester.

I think most people understand  mistuning or load faults are 
the most common source of arcs in PA's. It is a measurable and 
repeatable event.
73, Tom W8JI

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