[Elecraft] KX1: Replace R30 22 Ohms with 33 Ohms?

[Phil Wheeler]

Ron,

I see your point.  It's a bit academic at this point.  I made more 
progress yesterday than expected, so when I got to R30 I installed the 
default one (not having the alternate value on hand).  If I get the 
rated output, I will not do an R&R -- and I'm close to finding that out!

73, Phil

Ron D'Eau Claire wrote:

>R30 is a swamping resistor in the base of the final stage that holds the
>gain down and so keeps the stage from being over-driven and/or having enough
>gain to become unstable. It sounds like variations in the hFe of the output
>transistor are responsible for some of the power variations that are being
>reported, since increasing the drive by raising the value of R30 fixes the
>problem.
>
>Now, if the hFe of the final is low, then raising the value of the resistor
>shouldn't cause a problem. What I'd be concerned about is whether the stage
>remains unconditionally stable if the final has a high hFe and the value of
>that resistor is raised - allowing it to exhibit even greater gain. 
>
>My "guess" would be "yes", since the drive pot (R4) is in parallel with that
>resistor. So for a transistor with higher gain one would turn the pot so the
>wiper is closer to the ground end of the pot to reduce the drive and keep
>the output power at  the right level. Turning R4 to reduce the drive reduces
>the resistance to ground and improves the stability of the stage.
>
>The tricky part would be if someone tried to "QRO" their KX1 by
>reducing/removing that transistor in order to get more than the rated
>output. Not only would the stage have higher gain, the output matching
>circuit wouldn't be optimum any longer which promotes instability as well.
>
>My KX1 has rated output (with R30 at max where Wayne suggested putting it)
>and I don't have any spare finals around to try if it gets unstable, so I
>haven't tried it myself. 
>
>Ron AC7AC
>
>-----Original Message-----
>
>Since I'm still in the process of building, and will likely finish this 
>weekend, I am curious whether or not to do this replacement on my KX1.
>  
>