Electronics prototyping PCB

Was it a OC71 with the paint scratched off making it a phototransitor OCP71

Reply to
whisky-dave
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Which I learned recently was actually only possible with the OC71s that were actually rebadged OCP71s that had failed the opto transistor test, and hence were passed onto the "normal" OC test line to see if they would still pass as a 70, 71 or 72.

The ones made as normal transistors in the first place were potted in an opaque insulator before being put into the glass envelope and painted, so those ones would never work as a photo transistor.

Reply to
John Rumm

that's different to the usual story, fwiw.

NT

Reply to
tabbypurr

That wasn't my experience at the time - all and any could be scraped - things might well have changed over the years.

Andrew

Reply to
Andrew Mawson

No.

Originally OC 71s were in black glass, OCP71 in clerr. Then they started filling the OC71s with blue gunk, probably to help them stay cool, as much as opaque.

Reply to
The Natural Philosopher

The ones I hacked had an opaque jelly in them. I filed round the base, lifted the tube off, washed it in alcohol and glued the base back on.

Reply to
Bob Eager

Indeed, but I seem to recall that an ex Mullard employee had a somewhat more detailed and plausible account somewhere. Let me see if I can find it...

Ah, try:

"Like other manufacturers, Mullard produced a phototransistor, the OCP71 shown on the left. This is a very early type, available commercially from 1956. It is well-known that semiconductor junctions can be light-sensitive, and there is a widely repeated story that the OCP71 was just an ordinary OC71 without the black paint ('dope'). Because the OCP71 was more expensive, some people just scraped the paint off an OC71, to create an equivalent to the OCP71. The story then claims that Mullard changed the filler in the capsules from clear to opaque, to prevent this practice.

Thanks to correspondence with an ex-Mullard employee from the Mitcham works, I now know that this story is entirely wrong. "

you can read the rest here:

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Reply to
John Rumm

Crikey. Just how bad did they have to get to be only a red spot?

Reply to
Dave Plowman (News)

Yup that sounds more reliable than just taking the black off since the putty and alundum filling would be opaque otherwise.

Reply to
John Rumm

I didn't do anything clever with them - I think I just used them as on/ off. I had a copious source of OC71s at the time, so it was cheaper than buying an OCP71, or even an ORP12.

Reply to
Bob Eager

No, the blue gunge had originally been a by product of some chemical process and had the interesting property that it was highly elastic if squashed suddenly, but flowed if gently squeezed. So easy to get in the encapsulation, but an excellent shock absorber. It was actually a poor heat conductor. Later is was marketed as 'Potty Putty' - you could roll a bit in your hand into a sphere then use it as a very bouncy ball!

Andrew

Reply to
Andrew Mawson

A "non Newtonian" fluid by the sounds of it.

That would be why the man from Mullard called it "bouncing putty" I guess ;-)

Presumably why they added the alox / silicon oil to fill the rest of the enclosure.

Reply to
John Rumm

Not seen that but VERO used to make a development board .. used these a fair bit:

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I still have my Phillips Electronics Engineer sets .. they had a peg-board style sheet - you overlaid cct diag and springs pushed through holes, into which you slotted component leads. Remember making radio etc.

Still have both sets in original boxes with all components - maybe I should put them on eBay

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Reply to
rick

Good God. I got started with one of those.

Reply to
Bob Eager
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I owned one. Although I built all the projects, for some reason it didn't "stick", and I still have a blind spot with electronics to this day.

Reply to
Huge

More and more stuff is being made in just surface mount rather than dip/dil.

sometimes we have to buy these sorts of things :-

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Reply to
whisky-dave

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