HEP722 - never more trouble finding a datasheet

[zjokka]

found mention of this SI N type bipolar transistor, but cannot find the datasheet at alldatasheet.com or nte.
how do I know if it is a valid part number at all?

only found this - should i register?

http://www.eca.de/html/HEP/HEP722.html

the circuit works fine with other NPNs, so that's not the problem.
just curious about the HEP series? I believe is manufactured by Toshiba

[zjokka]

did find some items, but th HEP16xx or HEP8xx are not even transistors!

sortof a desperate bump because  Google is even at a loss suggesting me a bulk order

I'll keep looking though

[R.G.]

HEP is not a Toshiba product, unless they have started recently. In fact, HEP parts are not and never were manufactured.

Back in the days when dinosaurs roamed the earth and I was getting my undergraduate degree, Motorola had become a preeminent manufacturer of transistors. Motorola got its start in car radios - Motorola - and shifted into making other electronics, then semiconductors. Back then there was a market for replacement transistors and such, much what NTE does today. Motorola competed by relabeling their own transistors with "HEP" number. I think "HEP" stood for "Hobbist... (something or other)... (Parts or Package)" but that's quite a dim memory.

HEP products were designed into some DIY magazine cirucits because they made finding a suitable part easy for beginners. They were too high priced to be used in production electronics. They got used in some repair shops, and so if you find them in commercial electronics, the part is a replacement.

And this is the reason you can't find datasheets - there weren't any, or at least I never saw any, and I looked. The datasheets all were for the basic devices Moto made, and the info on the HEP parts was a condensed form, only the barest "Vceo/Vbe/Icmax" kind of thing printed on the packages and selection guides. HEP was discontinued decades before there was an internet, and what little info there was never made the jump.

It is possible that someone somewhere has done a labor of love and scanned the old info they might have accidentally still had, but it would be chance if that has happened.

[zjokka]

thanks so much for putting me out of my misery, RG.

then these circuits got dumped on and disseminated on the internet. Luckily the file name hints us at a 2n4401 which doesn't really make me happy.

[dxm1]

"Funk Box". Heh. Might be interesting to simulate this one. Wait... is that a BMP tone stack I see???

[R.G.]

No, it's not a BMP tone stack. It's an oddly drawn Twin T feedback network. That gives a notch in the feedback at the network resonance and so a hump in the forward response. It's a fixed-frequency wah circuit, frequency set by the pot.

[kx50002]

Hello, I've lurked here for awhile and recently began to experiment with some of the knowledge obtained.  I've built the effect mentioned here and it doesn't seem to do anything, neither the 2K trim pot nor the 10K range pot have much effect. I could not find an hep722, so replsced it with a 2n4401, also tried every NPN in my assorted boxes of parts.

Any help?

[PRR]

> I've built the effect mentioned here and it doesn't seem to do anything

Nothing? Does not smoke? Does not eat power? Does not pass signal at all?

> hep722, so replsced it with a 2n4401, also tried every NPN

Barking up the wrong wild goose.

> I've lurked here for awhile

Welcome!

And after lurking, you know that "doesn't do anything" is NOT enough clues for anybody to help you.

Read the DEBUGGING sticky-post at the top of the forum.

This one is so simple and so tolerant that I've even marked the expected voltages for you.



What parts-values did you change? (0.05u is out of style; in this case 0.047u or 47n will work the same, but there may be other parts which matter.)

How's your wiring and soldering? No offense intended, but "most" problems (even with skilled builders) are wrong or bad connections.

S1 has to be open. Omit it for now.