EMRFD Message Archive 906
Message Date From Subject 906 2007-07-21 07:01:01 wbdmxbaileybobbut... power amp need some help:
I am working on a power amp circuit in the DC40A qrp transciver.
the output stage is similar to the fig 2.10.
the problem I am having is that I have a good display on my scope at
the gate showing a good drive signal.
but I cannot see any display at the output at all.
I also have the same problem with the hands on circuit that was in qst
a short time ago that uses a 40 meter xtal and a buffer amp going to a
final amp that uses the feadback toriod transformer in a similar
circuit, I cannot see the output in that one eather.
I feel that if my scope can see the input, it should also be able to
see the output, or am I missing something here.
907 2007-07-22 08:36:24 Allison Parent Re: power amp 908 2007-07-22 08:38:38 w4zcb77 Re: power amp I also have the same problem with the hands on circuit that was in
> a short time ago that uses a 40 meter xtal and a buffer amp goingto a
> final amp that uses the feadback toriod transformer in a similarto
> circuit, I cannot see the output in that one eather.
> I feel that if my scope can see the input, it should also be able
> see the output, or am I missing something here.GM Bob. It may well be that there is a DC voltage on your output
that offsets the scope trace to a point where the trace cannot be
seen. You can determine that. Does your scope have both a DC and an
AC input? If so, be sure it's on AC or decouple the output of your
amplifier with a series capacitor.
Secondly, are you certain that the trace is NOT there but simply of
an amplitude that the screen cannot display? Again, the trace being
MUCH "taller" than the screen and you're getting a very dim display
due to the speed of the trace in amplitude?
Is the amplifier well behaved? Do not overlook the possibility that
it may be unstable and your scope is telling you that there is a
large output signal with or without input.
And one last thought, if the scope is a triggered scope, can you
obtain an image by changing the trigger control?
909 2007-07-22 08:57:25 Leon Re: power amp ----- Original Message -----
910 2007-07-22 14:43:57 wbdmxbaileybobbut... Re: power amp 912 2007-07-26 22:55:14 Bill Noyce Re: power amp When you say
> but I cannot see any display at the output at all.I interpret that as an oscilloscope trace that's a straight line,
though others seem to interpret it as a blank display. Which do you
Is there any chance you've confused the pinout of your FET, so you're
putting the input on the drain and looking for output on the gate (for
What are the actual input and output voltages you're seeing?
-- Bill, AB1AV
913 2007-07-29 17:00:08 wbdmxbaileybobbut... Re: power amp