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From: Tony Williams
Subject: Re: Amplifying stage with *negative* Voltage gain??
Date: Tue, 10 Dec 2002 13:52:56 +0000 (GMT)
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NNTP-Posting-Date: Tue, 10 Dec 2002 13:58:17 +0000 (UTC)
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In article ,
Paul Burridge wrote:
> opined thusly:
> > Which is still pointing to more load on the output
> > 1nF than you have so far discovered. It could be a
> > capacitance, or even something more absurd... any
> > chance that the scope is stuck on 50-ohm input-R?
> I've just checked on the scope input itself and it says "1M Ohm [in
> parallel with] 30pf" earlier someone said it should be nearer 10M.,
> but this is *definitely* just 1M (as opposed to the probe itself which
> is higher - certainly on X10).
> The only other source of capacitance would be two tracks of copper
> 2.5" long on the stripboard I've used to build this thing. They're
> certainly in parallel with the 1n, but since we're only talking of the
> low megahertz here, I wouldn't have thought that would be a problem.
Your reported "flattened bottom half" is suggestive
of a capacitive load on the emitter.... either the
1nF and a load outboard of it, or a direct capacitor
on the emitter.
Lift the emitter and the emitter resistor up off the
stripboard, join them together in mid-air. Connect
nothing else there. There is clearly then no load of
any sort on the joint. Look at it directly with the
scope only.... X1 and X10. See what you get.
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