unijunction needed

I can't seem to find a spec on that part? Maybe if you knew some more information on it, like the Peak Voltage, valley etc on the emitter one could be dropped in.

I have some unijunctions in my drawers and as far as know, they didn't make to many different types.

Jamie

As someone else pointed out there's no spec coming up for that part #, but it has the look of the type of number you might find on a PUT.

If that's the case and you only want 1, its easy to re-construct the same effect as the 4-layer device with a cross coupled complimentary pair of BJTs.

If you can put a schematic somewhere like A.B.S.E it may be possible to work out whether the circuit for a conventional unijunction can be modified for a PUT (or 2-BJT equivalent).

There's a few links here might be helpful:

I don't know anything about the device. I have a delay timer/relay that is supposed to activate a cryogenic compressor after a roughing pump has run for about one minute. It suddenly stopped working. I opened the timer/ relay.

It is a Potter Brumfield CUF-41-30120.

It has very few components wired up between 8 contacts or so. I have replaced the capacitors (two of them) and the diode checked out fine, but I put a new one in anyway. The resistors look fine, I have not tested them yet nor did I plan to. I believe the coil is fine, but I will have to unsolder a few parts to make sure I am not reading this wrong. The prime suspect right now is the MSU 112-2, which I have been told is a UJT, perhaps a PUJT (PUT). I wouldn't know where or how to measure the peak voltages/current..... I would be poking around inside a relay with

240 v and several amps behind it. Not something I want to do with the part installed on the device and the device running.

Ian, thanks for the links. If I study hard and long enough I will be able to come up with a replacement of my own manufacture. I doubt I have long enough to live however (I joke, but in reality my capacity to learn new stuff has dropped off significantly over the last couple of years). They should at least get me pointed in the right direction if I have to try (and don't wish to pay the 200-300 bucks for a new timer/relay).

Thanks all.

Alp

If this is just a stock delay relay module, why don't you just replace it with a new stock relay? Much easier than trying to source a part that has been obsolete for 40 years! If there's another reason that you have to repair this module, why not put a 555 or similar timer in there?

Jon

COST!!!!

Jamie

Yes, Jamie is correct, the cost of the device is ridiculous.

I would be able to build something (hack) if I could figure out how this circuit works. With all the pdf links I got from the other newsgroup posting I should be able to figure something out.

Thanks again ! Alp

Yep, >$200 is horrible. If you know the function(s) the relay must deliver, you can build a circuit to do it using current parts.

Some issues to determine concerning the function(s): You say that the relay must operate after the roughing pump has run for about 1 minute.

• What is the relay supposed to do if the roughing pump runs for less than 1 minute?

• Once the relay activates, how/when is it supposed to de-activate?

• How much current at what voltage must the relay switch?

• How many poles must the relay switch?

If you have room in the machine, and are willing to re-wire a bit if necessary, delivering the functions you need with an external circuit is a piece of cake, provided of course that you know those functions. OTOH, if you must create a drop-in replacement for (or repair of) the bad part, that can be a PITA.

Ed

The PUT was much touted as being more stable and better for long delays than the old style 2-base unijunction.

You stand a better chance of getting hold of a PUT these days - and if you can't, its easy to do the same thing with a complementary pair of transistors.

The circuit is easier to design as well, while the old style unijunction has a set trigger point (subject to inevitable device tolerance) the PUT is basically a thyristor with the gate at the anode end instead of the cathode end.

Basically you set the trigger point where you want it to be (within reason) by connecting the gate to a potential divider across the supply, the anode goes to the C/R as did the "emitter" of the old style unijunction.

As the C charges up to the trigger point; the anode becomes positive wrt the gate and the PUT fires and develops a pulse across the cathode resistor.

Thanks for taking the effort to explain. I managed to download a bunch of files explaining this sort of thing as well, but my main background is chemistry, not electronics. I know what the words mean, but they don't make much sense right now. Maybe I'll get lucky and find out it was the tantalum capacitor that went bad.

Alp

Tantalum caps can throw the odd curveball!

Any reverse voltage applied can make them go leaky, so apparently can rapid DV/Dt that can occur in some SMPSU applications.

Tants attract their share of discussion in these groups.

If the capacitance isn't very high - say 10 to 15uF; you can get multilayer ceramic chip capacitors that far exceed the quality of tants, readily available as SMD parts but if you search for them they can be found as resin dipped leaded types.