Greg Mayman wrote in a message to Roy J. Tellason:

 -=> Roy J. Tellason said to Greg Mayman
 -=> about "*BIG* TRANSISTORS" on 02-12-04  04:06.....

 RJT> No,  the data sheet specifically mentioned vcr and audio cassette
 RJT> applications. I can see reversibility being a good thing if you're
 RJT> running a tape cassette and have a bidirectional capability in the deck
 RJT> -- you'd have the mechanism switch capstans, but the motor would also
 RJT> need to spin in the other direction.  VCRs? Hm,  that's a little more
 RJT> difficult, I'm not that up on the mechanicals of those.

 GM> The only reversable cassette player I've looked inside has the
 GM> motor running one way all the time. The belt drive is arranged so
 GM> the two capstans are both turning at all times, but in opposite
 GM> directions. The pinch wheels and reel feeds are controlled by a
 GM> solenoid operated mechanical flip-flop.

I guess that'd be one way to do it...

 GM> The only place I can think where you'd need a reversable motor with
 GM> braking in a VCR is in the loading mechanism.

Yeah,  that'd be one place.  Maybe in the capstan too?  I don't know enough
about VCRs to be able to say,  but there are times when they do reverse
those, for those slow-motion functions and such.

 GM> Years ago I saw a cassette player that could load and change 
 GM> bewteen a stack of cassettes -- that would have needed a loading 
 GM> mechanism.

I've never seen such a thing,  though I keep hearing of such stuff from
time to time.  For magnetic cards,  floppy disks,  tape cartridges, 
whatever,  sooner or later somebody will try to build a "jukebox"
for them.

 GM> One intersting thing that the owner told me was that he could have
 GM> bought an add-on that would take each cassette as it was ejected,
 GM> and move it to the top of the stack, flipping it over on the way.
 GM> So you could have continuous playing of up to 10 cassettes, all 
 GM> the "A" sides first then all the "B" sides,
then repeat...

I have a fair amount of stuff on tape,  but don't listen to it much.  I
guess having CDs playable through any number of computers has rather
spoiled me for sequential access.

 GM> I remember them!

 RJT> Yeah,  weren't they nifty?  :-)

 GM> Yes. We don't seem to have any true analog displays these days.

Even real meters are too expensive,  it's cheaper to throw a chip and 3-4
LEDs at something.  :-(

 RJT> Vaseline?  First time I've heard of that being used for the purpose...

 GM> I heard of one couple that used it for sexual purposes... they
 GM> greased the bedroom doorknob to stop the kids from bursting in.

Heh.

 GM> I always keep a jar handy... for strictly technical purposes you
 GM> understand.

It's handy.

 RJT> I've used all sorts of assorted spray cleaners over the years.

 GM> They work for a while, but they tend to dry up. An inert grease is
 GM> the best as it will coat the track. The wiper can press the grease
 GM> aside (if it is not too thick) and the grease will reform the seal
 GM> behind the wiper.

 RJT> Transformers fall into the category of inductors,  a class of
 RJT> components that I've seldom gotten along with over the years.  :-)

 GM> They can be a real bugbear.

Yep.

 GM> I once salvaged a transformer that had burned out, only because it
 GM> had a low loss core. The laminations were made in one piece in the
 GM> usual [|] shape but the only break was across one end of the centre
 GM> leg where it met the outer ring. I cut the old windings out of the
 GM> former and rewound it to 7 turns/volt to suit the core area. but I
 GM> must have made a miscount somewhere as the secondary gave a lot
 GM> lower voltage than it should have.

 GM> When I did some tests I found it was closer to 10 turns/volt! 

 GM> I never could use it for the purpose I intended it for as there
 GM> wasn't enough room left to get the volts I needed and it was too
 GM> much trouble to remove the laminations, strip off the secondary,
 GM> strip some of the primary and rewind the secondary.

Winding transformer always struck me as rather too much trouble.  :-)

 GM> That was an interesting project -- an audio amplifier with a class
 GM> AB output driving a class C booster, using all discrete
 GM> transistors.

Hmm.  And transformer-coupled?

 GM> The performance was quite good. The distortion was surprisingly low
 GM> considering the output stage, but I can't remember the
 GM> figures now.

The figures probably wouldn't mean much to me anyhow,  I've never been one
for that particular numbers game.

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