SE topology
On Oct 10, 5:40*pm, Big Bad Bob BigBadBob-at-mrp3-
wrote:
On 10/07/10 04:21, GRe so witilly quipped:
Has anybody tried or seen a SE topology as shown below?
hmm...
has anyone ever considered a rotating 'phase selector' switch that
clicks over each time you power up the unit? *The idea would be to swap
the phases on both primary and secondary each time you power up the amp,
thereby (to some extent) 'equalizing' the magnetization of the core in
both directions to prevent it from building up in one particular
direction (and killing your output). *OK, so you'd have to make sure it
was a "one shot on power up" switch, but something like that isn't
impossible to make, like a solenoid that rotates the switch whenever the
unit energizes (you'd do this during warm-up so there's no arcing in the
switch).
I've seen the effects of magnetization before, having once 'flipped'
both output transformer windings (both pri and sec) on an ancient stereo
system that had a dual SE pentode output stage. *Prior to the flip, max
volume was barely audible. *After the flip, worked perfectly. *The
stereo had a nice cabinet, hinge top with turntable (built some time in
the early 1960's I think). *Lost track of it years ago, so I don't know
if it still works.
You have raised an interesting issue of core behaviour. What you are
saying is that SE OPT cores gradually become magnetized in one
direction, and the core mysteriously inhibits signal passage by means
of presumably core saturation or collapse of primary inductance in a
way similar to that caused by a group of shorted turns somewhere.
After working in hi-fi repair industry for 16 years I have never
encountered the phenomena you speak of. I have dealt with very many SE
amplifiers and old radios with SE OP stages and found none to have
core materials requiring phase reversing to "re-juvenate" audio
performance. While my electronics was a hobby when I was a teenager
in the 1960s I never found any of the many SE OPTs I fiddled with
needed reverse phasing to improve audio. A friend and I often used a
6V6 and SE OPT from some old radio to modulate the RF cathode current
of another 6V6 used for an SE RF output stage. With cystal mic and
headphones we made our own radio telephone, albeit on an illegal
frequency band - until the fad wore off and we discovered girls, jobs,
and Life.
One would think I might have noticed misbehaving core materials but
afaik all core materials never become permanently magntized in one
direction.
Patrick Turner.
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