Hi JIM.

27-Dec-02 08:20:00, JIM HOLSONBACK wrote to JASEN BETTS


 JH> Hello, Jasen.  Thanks for responding.

 JH>> I ended up blowing it up - - I'll tell about that later.  Took it
 JH>> apart, and the only thing in there which could possibly be a
 JH>> rectifier is this lightbulb-looking thing, with 2 bare leads out
 JH>> of the bottom of the glass, and wired to the circuit board.

 JB>> Circuit board, I guess that means it's not old enough to have a
 JB>> metal-oxide rectifier stack in it   (looks like a buinch of metal
 JB>> plates with a brass rivet throught them and 4 wires attached)

 JH> Nope, and actually there isn't really a circuit board.  all the
 JH> components, what few there are, connect to an old fashioned
 JH> terminal strip.

 JB>> That one wasprobably a real light bulb.  they make a handy
 JB>> current limiter for trickle chargers.

 JH> Nope, in that case also, the bulb-thingie was the only thing there
 JH> which could have been a rectifier.

 JH>> My questions - -1.  What the heck are these bulb things, and how
 JH>> much would a replacement for the unit at hand cost?

 JB>> the cost is small, the trick is getting the right one....

 JH> I expect they're hard to find now, having been superseded in the
 JH> market by the selenium type by about 1960.

 JH>> 2.  How can a rectifier with only 2 leads give good enough DC to
 JH>> run an auto stereo back in the home, without a lot of hum.

 JB>> I don't think it can, keep lookimg. trace the transformer
 JB>> secondary circuit, it's gotta go to the rectifier or possibly the
 JB>> on/off switch of fuse)

 JH> Done, and I'll have to make up a little graphic of the schematic
 JH> and post it later - - going out of town for a week, to check out
 JH> new grandson in Alabama.  :-).

 JH>> 3. Should I pitch the thing, or could maybe some large diode or
 JH>> diodes be added, which would make it useable again?

 JB>> if it's got a dead lightbulb it needs a new one,  check the one
 JB>> you have for clues. for low voltage ones the colour of the glass
 JB>> bead on the filament supports indicatees the voltage.

 JH> This is not a standard lightbulb.

 JH>> FWIW, in desperation, after probs with the riding mower, I used
 JH>> this unit for a battery charger.  It worked OK, and put some
 JH>> charge on that there lead acid battery, but I blew it up and 'let
 JH>> some smoke out" when I tried to crank the mower while this
 JH>> makeshift "charger" was still attached.

 JB>> you could have cooked the transformer primary, (I reecently did
 JB>> that by accidentallt to tow of my plug packs)

 JH> Transformer still OK - has 15-0-15 VAC at the secondary.

anything connected to the centre tap?
(a transformer like that is typically used for a push-pull rectifier)
(especially if you want about 14V out of it rather than about 30V )

 JH> I'll post diagram later.  There are two small parts there which
 JH> are clearly cooked.  The bulb think looks to be OK.  The secondary
 JH> side just has those two small parts (now blown), the bulb thing,
 JH> and a 4000 mfd capacitor.

blown things couldn't have been bead-shaped diodes?
what resistance do you get for the bulb thing?
could it be a bimetalic cutout?

I saw an al-chepo slot-car powersuply that used bead diodes and a
glass-encased bimetalic cutout. purchased in 1982 iirc.

 circuit omething like this:
          __  |||  ___---|>|---------  +ve
  _______/ _) ||| (_                                ><
           _) ||| (___.  ><                       __||__
  _______  _) ||| (_  |__||__--------- -ve        my symbol
         \__) ||| (___                           for the cutout
              |||     ~---|>|--------- +ve

 it had two half-wave positive outputs (to run 2 cars) but yiu could hook
 them together and get a full-wave recitfied output

 -=> Bye <=-

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