25 Nov
2011
25 Nov
'11
12:59 p.m.
On 24 Nov 2011 at 21:02, Tony Duell wrote:
I think that's right. A simple-ish demonstration of this (which I have
done) is to take a mild steel bar, wind a couil on it and connect said
coil to the input of an audio amplifier. Then magnetise the bar in the
traditional way by stronking it with one pole of a permanent magnet. You
get the Barkhausen noise as you stroke the magnet until the bar is fully
magnetised. Of course if you tehn remagnetise it the opposit way (by
strokign it with the other pole of the magnet) you can get the noise again.
For some reason the term 'Barkhausen
effect' is coming to mind. But
that may be a collision ib my hash tables.
Isn't that a magnetically-induced thing related to crystal
dislocations under a changing magnetic field? i.e., Barkhausen
noise.
I also think of early HF oscillators produced by placing the grid of
a triode at a positive potential relative to the cathode and the
plate at a negative potential. Called "Barkhausen" or "electron
orbit" oscillators.
I wnder if that's the effect. The metal film depositied on the inside of
the glass could become negatively charged due to electronics hitting it.
Also related are oddball oscillations in tetrode HF
power amplifiers,
I think.
There's the dynatron oscilalator (nothign to do with the UK radio company
of that name AFAIK) which depends on the negative resistance part of the
Ia .vs. Va curve for a normal tetrode. The beam tetrode was sometimes
called a 'kinkles tetrode' over here, because it doesn't have this dip in
the chracteristic curve, and the 'KT' in valve numebrs like KT66 and KT88
stands for 'Kinklrss Tetrode'.Needless to say those can't be used as
dynstron oscillators.
-tony