> 

> 

> 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