Re: [Amps] sb-220 non uniform grid current ??

[Dan Sawyer <dansawyer@earthlink.net>]

Thank you,

The exciter is a Heathkit 5400. In the last reading below it is driving 
the amp with about 30 watts. If I increase the input drive power from 
that point the grid current rises very rapidly and the output wattage 
flattens. Due to the cautions about grid current I have stopped there. 
(At that point plate HV has dropped to about 2KV) Is it feasible that if 
the amp were incrementally tuned it would return to a more linear 
relationship??

btw - ZSAC is about 100 ma on the CW/TUNE tap and about 150 on the SSB tap.

Dan

R. Measures wrote:

> **  Thanks.  These grid-I figures seem normal to me.  However, the ZSAC 
> (zero signal anode current) seems a bit low.   With the reduced anode 
> supply V on the CW tap, grid current is higher because the anode is less 
> attractive to electrons - so more of 'em go to the grid.  
> -   To fully drive a pair of 3-500Zs, it takes well over 100w.  
>
>  
>
> > Thanks,
> >
> > The following data was collected from an antenna with an SWR of about 1.5.
> >
> > Plate ma       Grid  ma
> > 100                0
> > 120                10
> > 140                20
> > 160                30
> > 180                40
> > 200                50
> > 300               100
> > 600               150
> >
> > These were obtained by carefully increasing the drive and incrementally 
> > tuning first load and then tune. These appear to be good results. 
> > Attempts to tune directly have to be approached very slowly and 
> > carefully. Is it possible the high grid current readings are a result of 
> > poor tuning skill on my part??
> >
> > Dan
> >
> >
> > R. Measures wrote:
> >
> >    
> >
> > > With 700 - 800mA key-down on the CW tap, what is the grid-I?  Tnx.  
> > >
> > >
> > >
> > >      
> > >
> > > > All,
> > > >
> > > > I have an sb-220 with non-uniform grid current. With low to medium drive 
> > > > grid current is linear (or apparently close to it) with plate current 
> > > > (minus about 100 ma base) and output power. However if input drive 
> > > > exceeds the medium level of 25 to 30 watts grid current starts to hockey 
> > > > stick "high". It is not a digital switch; but a very steep response.
> > > >
> > > > The components in the bias and grid meter side of the circuit have been 
> > > > checked in circuit. The grid bias coil has been replaced with an 1/8 
> > > > watt 33 Ohm resister.
> > > >
> > > > Thanks,
> > > > Dan
> > > >
> > > >
> > > >
> > > > _______________________________________________
> > > > Amps mailing list
> > > > Amps@contesting.com
> > > > http://lists.contesting.com/mailman/listinfo/amps
> > > >
> > > >   
> > > >
> > > >        
> > >
> > >
> > >      
>
>  
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