[ETO_Alpha] 91B Load Settings on 160M

[Dr. James C. Garland]

Dennis, 

If grid current is excessive, then that's usually a sign of too much loading
capacitance, not too little. You'll need to reduce the loading capacitance
in order to drive the amplifier to higher power output without incurring
excessive grid current.  You should pull the lid off the amplifier to see if
a "0" on the load control corresponds to minimum or maximum capacitance. If
it is minimum capacitance, then there's nothing easy you can do to decrease
the capacitance more. If it's maximum capacitance, then you just need to
turn the control up a little and drive the amplifier harder. 

73,

Jim W8ZR 

> -----Original Message-----
> From: eto_alpha-bounces at mailman.qth.net [mailto:eto_alpha-
> bounces at mailman.qth.net] On Behalf Of Dennis Ashworth
> Sent: Thursday, December 27, 2007 9:32 PM
> To: eto_alpha at mailman.qth.net
> Subject: [ETO_Alpha] 91B Load Settings on 160M
> 
> My 91B loading capacitor setting for maximum output on 160M occurs at
> a setting of zero, which I suspect is maximum capacitance. At this
> point, there is more grid current than I would expect to see so I
> must reduce to drive to prevent excessive grid current levels.
> Maximum power output is around 800W at reduced exciter drive. The
> load control setting at zero correlates with the final QC checklist
> which accompanied the amplifier from Alpha. Measurement are into a 50
> ohm dummy load.
> 
> Model 91B S/N983110748 shipped 12/08/98
> 
> I suspect additional capacitance is required to properly load the
> amplifier. Is this a reasonable assumption? Anyone else experience this
> issue?
> 
> Many thanks
> Dennis Ashworth, K7FL
> 503.706.8551 (cell)
> 
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