27 Apr
2011
27 Apr
'11
12:50 p.m.
Chuck Guzis [cclist at sydex.com] wrote:
I was very common ito the transistor/IC era. OK, sometimes you used a
thermistor not a light bulb, but the principle was the same. A couple of
examples off the top of my head :
The Philips EE1003/1004 kits have a project ot make a Wien bridge
oscillator using a filament lamp to stabilise the gain. That was all
discrete transistors
There was a Heathkit analoge electronics trainer (in the same series as
the well-known 6800 computer one), which has a built-in signal generaotr.
It's a Wein bridge circuit using an op-amp for the ampliifer, agian with
a small filament lamp tocontrol the gain.
There was a very xommon small audio sig-gne used in schools and
university undergraduate labs over here. Yes, a Wein bridge (although
oddly the capitro, not the resistor, was the variable part), using a
thermisotr for gain control.
There must be many others....
-tony
It was common knowledge in the 1930s. I have a "Radio Engineering"
handbook from the late 30s that shows the consutruction of an audio
signal generator using a common panel lamp for temperature
compensation.
I saw the technique used once in a Practical Electronics article
sometime
in the 1980s (or thereabouts). So I don't think it was forgotten, just
not used very often.