31 May
2008
31 May
'08
2:26 p.m.
Tony, that would be Jim Williams, Linear Technology.
Randy
From: ard at p850ug1.demon.co.uk
To: cctalk at classiccmp.org
Date: Sat, 31 May 2008 03:02:37 +0100
Subject: Re: Transformer repairs
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It is probably possible to build a current
limiter that provides
immediate visual feedback. I challenge you, or anyone for that matter,
to come up with such a design that is as cheap, easy, simple, and
foolproof as an incandescent bulb. (Well, not cheap once the ban hits,
which is the problem.)
Actually, this reminds me of another application... the audio oscillator.
As is well-known, it's very difficult to make an adjustable LC oscillator
at audio frequencies. An RC oscillaotr is possible, but stabilising it
(so you get a reasonably non-distorted sine wave output) is the problem.
Now many yeats ago, a guy working for Prof Terman (you do know who I
mean, right...) solved this problem. He used a Wien bridge circuit as the
'resonant element', in the feedback loop of a *3 amplifier. The gain of
the latter was stabilised by a light bulb as a non-linera resistor with
just about the right time constant.
Anyway, I read somewhere (possibly in one of Bob Pease's columns) that
somebody had tried to improve upon this circuit using a more modern
approach, an FET to cotnrol the gain, a carefully-designed control loop,
etc. The result was a an oscillator with a more distorted output than the
simple light-ulb-stailised one...
-tony