Available Audio UJTs?

[phdinfunk]

Hi,

Years ago, I used 2N4853s for audio frequency UJT.  I got the basic design out of a book in the university library at the time.  It appears to be out of production by now.  Are there any similar good audio UJTs around?

I can build using other methods, but the oscillator with a UJT kind of sounded like a buzzsaw.  I'd like to play with that again.

--Winter

[edavid]

There are not any left in production, at least outside of China.  They are also pretty expensive on eBay.

Has anyone tried these "BT33"s?

https://www.aliexpress.com/item/20pcs-lot-BT33F-BT33-semiconductor-triode-unijunction-transistor-double-base-diode-gold-seal-new-original/32813580282.html

[T3sl4co1l]

You can make identical waveforms with PUTs, a comparator, 555 timer, etc.

Tim

[chris_leyson]

Complimentary feedback pair is sometimes used, http://www.4qdtec.com/putpr.html

[technix]

This will sound weird, but some MCU can even be cheaper or smaller than 555's like STC15W100 in SO-8... So code one up? With that 8051 chip you can let the timer to do the actual output, and after setting everything up just put the processor part into sleep.

[simmconn]

That part number brings fond memory. It was about 30 years ago when I was in grade school. I built an electronic organ board using two BT33s, one for the main tone generator and the other for modulator. After a couple of days' debugging I still couldn't get it to oscillate. One morning my dad asked me to double-check the pin out. Yep, B1 and B2 were swapped. I was so happy to hear the tone and was almost late for school that day.
At the time precision resistors were scarce, even metal film resistors were considered expensive. So all my tone-setting resistors were 'scratched to value' from carbon film resistors of a little lower resistance then covered with paint. As you can imagine, they drift a lot even with the paint cover.

[orolo]

Complimentary feedback pair is sometimes used, http://www.4qdtec.com/putpr.html

Great! I toyed with this configuration years ago, but I concluded it was a bit unpredictable. Lately, I've been thinking about a Halloween "flashing red eyes" kit, as a kid's introduction to electronics, and the complementary feedback pair is perfect. Works from a 3V button battery, the glow is satisfying, really easy to build soldering point to point, compact (you can put it in hanging cardboard bats and all that  ), and best of all, I don't have to touch my dwindling collection of UJTs!

Edit: My collection of UJTs isn't dwindling that fast. PM me and I'll gladly send you a few for experiments. They're 2N2646.

[phdinfunk]

Hey, thanks Orolo!

I hadn't logged on for a few weeks as I've been very busy building things.  I would have taken you up your offer, but I did find a few 4853s.  Thanks, though.

While I don't have a scope, I think the sawtooths are different from just regular relaxation oscillators with a diff. pair.  They sound different, maybe chopped off at one power rail or something.  I'll have to experiment a bit.