Re: [Amps] AMPS

["Joe Subich, W4TV" <w4tv@subich.com>]

Rich writes: 

> >> K-202 looks like it's a grid shutoff.
> >
> > There is no K-202 on the schematic or parts list of the PA-374, PA-76
> > or PA-78 amplifiers on the BAMA site.  Those are the only amplifiers
> > produced by Alpha to use the 8874.  In all three cases the grids of
> > the 8874 are connected directly to the chassis.
> >
> > Which amplifier/schematic are you looking at?

Rich, where is K-202? 


> >> I was looking at Alpha's diagram.
> >
> > Apparently not the diagrams provided to BAMA by Alpha (W0UN 
> > and AE0Q).

Which diagram from Alpha? 

> Thanks. Since grid-current meters typically connect from the  
> cathode / neg-HV to gnd I missed this.
> 
> Does this circuit stop the flow of grid-current or just open the PTT  
> line?.

Rich, the manual clearly states if the grid-current overload occurs 
by itself the PTT is opened (which applies cutoff bias) since the 
likely cause is overdrive or mistuning.  If grid current overload 
occurs at the same time as a plate overload the HV is removed. This 
would deal with both an arc and parasitic oscillation.

In both cases the action is appropriate and will stop the flow of 
grid current by addressing the root cause. Pretty clear, well written
and easily understood. 

Now, what amplifier is it that uses a transistor to open a 50 A
grid circuit?   Specifics please - including URL to the schematic. 

73, 

   ... Joe, W4TV 
 
 

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