[Lowfer] LF: PA problem

[David Stinson]

-----Original Message-----
From: N1BUG
Subject: [Lowfer] LF: PA problem

I wonder if anyone can help me with this.

I built one of these:

http://qrp-labs.com/ultimate3/u3mods/lfamp.html

...I am only guessing but it seems like maybe the
PA is not properly 
decoupled from the power supply? Or perhaps it is
just unstable. Any 
suggestions? I need to make this work if I am
going to be on 2200 
meters this winter. I have one more FET and will
order a couple more 
but I would like to have some idea what to try
with the next one.
======

I'm not the expert, Paul, but IIRC, there should
be a ferrite bead
on the Gate and a resistor, about 15K, from the
Gate to ground.
Both of these are to "tame" the Gate and prevent
parasitic 
oscillations; those at VHF may not show on the
average ham's scope.
Again- I'm no expert, but that's what we used to
do long ago
when we first started using FETS on 160-190 KC.  I
do remember
building a FET PA without the 15K Gate-loading and
it self-destructed
in short order.  The 15K got it working.  That was
a long time ago
and perhaps newer FETs don't need it.   Someone
here smarter 
than I will know.

73 Dave S.