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
(https://i.postimg.cc/QFsFVNtS/IMG-0507.jpg) (https://postimg.cc/QFsFVNtS)
(https://i.postimg.cc/kBWVnRnB/IMG-0508.jpg) (https://postimg.cc/kBWVnRnB)
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.
(https://i.postimg.cc/gjSZ78zQ/allglas-trans-46.gif)
Yes, strong light will overwhelm bias and signal, this being the phototransistor version.
White stripe is Collector. Note the light sensitive area is on the side not the end.
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.
(https://i.postimg.cc/qh9XkX4J/clipimage.jpg) (https://postimg.cc/qh9XkX4J)
Quote from: amptramp on November 26, 2021, 07:10:36 AMThis 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.
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
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
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