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[GenePink]

Awwwww, the poor, maligned, misunderstood, and all but forgotten;  "Programmable Uni-junction Transistor".

Over the decades I have doodled with a circuit design to make a handy battery powered pocket tester. The premise was to make a free running oscillator, where the frequency of the oscillator would vary based on termination impedance.

Ideally it would provide recognizable frequency discrimination between 0-2-4-8 ohms, all the way up to 600 ohm-2k-10k-higher. Obviously a nonlinear scale.

The oscillator would make enough output to actually be audible (while not very loud) when connected to a speaker, while not so loud, that it would cream a mic input.

I planned to use a square wave, or some variant waveform, so even a LF pitch, could have MF and HF output to exercise all loudspeaker drivers.

John, or any else interested in building your own shit along these lines, this may be of interest:

http://talkingelectronics.com/projects/UJT/UJT_Page.html

Adjust component values to taste. Not quite an ergonomically pleasing result, as lower Z driver loads will result in higher pitched squeals. Meaning a 20K ohm amp input load would sound like a fat guy home brew beer fart, but still usable as a test source. Since for amp input "yes-no" testing you are not likely to give a shit about the exact input Z, a 1K or whatever resistor shunting the output to ground on this circuit will prevent the beer fart sound and turn it into a low tone. The sawtooth cap discharge pulse train is loaded with harmonics, and the circuit is sure simple enough to build and works well off of a 9V battery. Good enough for a "yes-no" test if the driver in question is right in front of you, although flown in a quiet arena you can still hear them, you just can't really tell which exact driver it is, just that it squalls. 

It'd probably run just fine off of an itty bitty little A-23 12V cell with a 47uF cap in parallel, to stiffen up the supply, if you want to try to make it tiny enough to try to cram it all into an XLR shell. Instead of fucking with all that, for this sort of thing, I usually just go with a male xlr connector and a few inches of Belden 8412 permanently connected to a 1X2X2" project box. Not slick looking, but I'm not trying to impress anyone with style, I just want it to work when I need it. And it fits in your pocket or ties to a belt loop.

My first phase popper was based on something like this and toward the end of building it, I realized that by switching in a much smaller capacitor to buzz at about 30Hz, it was also now a troubleshooting device. I have adapters for EP6, EP8, and later on, Neutrik 4 and 8 to check all the bins at loadout on the way to the truck. Just ran all the drivers at the same time per the adapter, put my ear close and listened to then one at a time: "Heeeee, Heeeee, Bsssss, Tzzzzz, Tzzzzz" (12", 12", 2", tweet, tweet). Yeah, good, load it out. It has one rotary switch for power and output attenuation, marked "Off, -30dB, -10dB, +4dB, SPKR". And the 0.3Hz or 30hz toggle switch for phase popping, per the original plan.

Anyway, food for thought.

Gene Pink

[John Roberts {JR}]

Pink... Wouldn't a programmable uni-junction transistor be a PUJT? and if it's a uni-junction why does it have two bases..? :-)

I remember those from back when,  but never used one in a design.   

I hope you are doing good, it's been a while.

JR

[Geoff Doane]

I use an original MR1 Minirator for tests like this.  I think it meets all the criteria except for being really small.  The LCD is also a failure point if you're not careful with it.  I think it cost about $200, ten or so years ago.  The original didn't connect pin 1 to anything, and since it's in a plastic case (isolated from the outside world), phantom power doesn't bother it, and it drives balanced inputs without a problem.

Unfortunately, the replacement doesn't have the built-in, swing-out male XLR, so you'll need a short cable, or you could "permanently" fasten a barrel adapter to its output XLR.

GTD

[GenePink]

Pink... Wouldn't a programmable uni-junction transistor be a PUJT? and if it's a uni-junction why does it have two bases..? :-)

I remember those from back when,  but never used one in a design.   

I hope you are doing good, it's been a while.

JR

"two bases?" Must be a ground rule double. Umpire said "take your base" so I did. Got stopped at the gate, they were pissed, had to go put it back. They should be more clear on these things.

I would guess a unijunction because it doesn't have a collector. I think the programmable idea came from that they were trying to come up with a variable threshold diac to drive triacs and such, and if you check out the link I posted, they call it a "UJT Transistor", aptly named by the Department Of Redundancy Department.

I still get on here and lurk every now and then, just don't really have the time these days. Speaking of those unheard from in awhile, whatever happened to Andy Peters?

PS: I'm a "newbie" 'round here?

Gene

[John Roberts {JR}]

I see Andy post on another forum from time to time but not as active as he was here, back in the day.

I'll PM you his email.

JR

[Martyn ferrit Rowe]

Hey Guys,
you could build this into a small bud-box powered from a 9v battery.
Either a captive cable or a turn-around xlr extension

http://www.vellemanusa.com/products/view/?id=350540

cheers
ferrit

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