Author Topic: OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?  (Read 293 times)

Toy Sun

OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?
« on: November 25, 2021, 07:14:48 PM »
Hi,
I'm building a Hudson Broadcast (PedalPCB) and bought an OCP71 from eBay. I can't identify the pinout, but my guess is that the white stripe (sorry, blurry photo and ignore the "V") is the collector. The pins seem to be evenly spaced, so I can't figure it out by grouping. Any insights? I've installed a socket, so if I install incorrectly, it won't damage the component, will it?

2nd question - should I paint this transistor black to block out light? It will be inside an enclosure, of course....

Thanks,
John
 




PRR

Re: OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?
« Reply #1 on: November 26, 2021, 01:09:07 AM »
https://www.radiomuseum.org/tubes/tube_ocp71.html

One pin is further out, surely? Yeah, it is a 4-hole base with 3 legs inserted.


Yes, strong light will overwhelm bias and signal, this being the phototransistor version.
« Last Edit: November 26, 2021, 01:11:08 AM by PRR »
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tonyharker

Re: OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?
« Reply #2 on: November 26, 2021, 07:02:57 AM »
White stripe is Collector. Note the light sensitive area is on the side not the end.

amptramp

Re: OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?
« Reply #3 on: November 26, 2021, 07:10:36 AM »
This presents the possibility that the device characteristics could be controlled by a light source made from a LED and a variable resistor or the LED could be fed from the amplified signal giving a distortion that is programmable.  Lots of fun to play with this.

tonyharker

Re: OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?
« Reply #4 on: November 26, 2021, 07:18:13 AM »



PRR

Re: OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?
« Reply #5 on: November 26, 2021, 01:00:54 PM »
This presents the possibility that the device characteristics could be controlled by...

Does about the same thing as a current into the Base. Without the inefficiency of a light source.
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iainpunk

Re: OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?
« Reply #6 on: November 26, 2021, 05:25:21 PM »
you can actually inject signal into the light sensitive spot using an LED, or just use light as its bias. i decapped a (already damaged) ASY29 Ge transistor once to experiment with light injection. i suggest not paining the transistor, but packing it in paper and electricians tape to block out the light without devaluing this transistor (nor monetary value, but historic).

cheers
half man - half snail - 6 feet to scale - Snail man's - not frail - He's been - to jail - snail man is fuccing real
『snailpilled』

Toy Sun

Re: OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?
« Reply #7 on: November 27, 2021, 04:19:18 AM »
Thanks all, good advice. I ended up finding a gutshot on the PedalPCB forum where someone did a clean build with one of these and I could confirm the orientation. It is running and sounds great.

Best,
J

iainpunk

Re: OCP71 (OC71) Identify Pinout and Use in "Transparent" Form?
« Reply #8 on: November 28, 2021, 09:23:33 AM »
ow, i just now see that i forgot to write this in my last post.

lots of transistors are somewhat reversible, but what happens differs per type. a lot of older OC series Ge transistors lose about 10% to 30% of their Hfe, most Si transistors lose a whole lot more, the 2n2222A i tested lost about 65%-ish of its gain.
some Ge transistors stop working altogether tho, like the OC171, and other have so much leakage that the Hfe gets dwarfed in comparison...
i think the OC71 would work within spec when you flip E and C pins. also if you put it in a socket, you can choose forward or backward based on your own taste

cheers
half man - half snail - 6 feet to scale - Snail man's - not frail - He's been - to jail - snail man is fuccing real
『snailpilled』