My comment about seeing no voltage on Q7 was before I discovered that I had
wired the Trifilar wrongly. Since correct placement I now see voltages. however,
it seems my replacement pot is faulty, and I have to find another.
R20 is correct.
I’ll report back when I have a working R1 pot.
Thanks to you and William.
Patrick, you did write 2 days ago, that: No voltage seen on Q7 whatever the position of
That is not correct behaviour.
Also you say that R1 gets smoking. Not correct either, as R20 being 3.3K
Sounds like the slider of R1 is shorted to something, likely ground, as smoke
gets there when you turn the slide very close to +5V end. Also do check that R20
is 3K3 = orange-orange-black-BROWN-brown,
and not 330ohm.
Normal behaviour, and easy testing, is
Step1: Do measure total current to whole PA, and while current is below 100mA
try to raise R1 somewhat, like until max halfway.
Step2: Put R1 slider turned one fifth. (No smoke? Check) Now measure voltage
on slider. It is 1 Volt. Has to be about there, not zero, not 5V. And also
measure Gate voltage on Q7. Has to be exactly the same as on slider. That
is,both ends of R20 has 1Volt.
PS: Step2 can as well be done without Q7 mounted, just to check that the rest
of the wiring is correct.
73 Christen Fihl, OZ1AAB