2N2646 UniJunction transistor - what is it and how does it work?

KL7AJ

Joined Nov 4, 2008
2,229
It's commonly used as a trigger for an SCR or as a relaxation oscillator (which is it's purpose in your application).
Here's an explanation of the device.
In my vast component archives, I have precisely one 2N2646. Trying to figure out what I want to do with it. Probably make a code practice oscillator. :)
 

KL7AJ

Joined Nov 4, 2008
2,229

ian field

Joined Oct 27, 2012
6,536
I was just looking at PUT's. But what has me confused is the "Programmable" part in the description. And I'm assuming the lead pin-out is the same as the UJT.

OR maybe I could replace it with an SCR. What'cha all think?
The Programmable" bit is the voltage divider you take the anode gate to. As the capacitor charges, the anode rises above the gate and the device triggers.

The complementary asymmetry means that you can build a circuit that works on the same principle with a TO92 SCR like the 2N5061 etc - you pretty much turn everything upside down.
 

AnalogKid

Joined Aug 1, 2013
10,986
Not quite as rare as that, but out of production,
OK, as long as the geezers are wagging and bragging, I'll chip in. No only do I have a tunnel diode, but I actually got the tunnel diode FM wireless mic circuit in the GE Transistor Manual to work - exactly once. Post #12, p. 357.

ak
 

OBW0549

Joined Mar 2, 2015
3,566
OK, as long as the geezers are wagging and bragging, I'll chip in. No only do I have a tunnel diode, but I actually got the tunnel diode FM wireless mic circuit in the GE Transistor Manual to work - exactly once. Post #12, p. 357.
Just think: you're probably the only person in Ohio to own a tunnel diode...
 

AnalogKid

Joined Aug 1, 2013
10,986
Just think: you're probably the only person in Ohio to own a tunnel diode...
Along with some other "classics". My inventory ... has personality ... is well seasoned ... has an eclectic flair ... is aged like fine wine ...

One of my bench supplies is based on a 2N2480 and an LM399.

ak
 

Bernard

Joined Aug 7, 2008
5,784
How did we get off to TDs- AH, I think that I still have a few- even used one back in 1965 to digitize return radar echo of ECHO satellite.
 

RichardO

Joined May 4, 2013
2,270
OK, as long as the geezers are wagging and bragging, I'll chip in. No only do I have a tunnel diode, but I actually got the tunnel diode FM wireless mic circuit in the GE Transistor Manual to work - exactly once. Post #12, p. 357.
ak
When I got my Tek475 scope I wanted to check the calibration. To test the risetime I built a tunnel diode oscillator. I was real disappointed in the results. I expected it to be a lot faster than it was. (Might have been my problem and not the tunnel diode's...)

I built a avalanche pulser using a 2N2369. It worked a lot better than the tunnel diode. I was able to see a 1.2ns risetime. Tek spec's 1.4ns. :D
 
Top