On 6/11/2019 7:56 AM, three_jeeps wrote:
A colleague drops by my office toating a Tek R293 Programmable pulse generator and power supply and asks "Can I use a power supply?" followed by, I haven't turned it on in 35 years....
Having never seen one of these before (its circa 1966) and thought it might be an interesting thing to restore, even though I have never and probably will never have use for such a thing.

Looking through the manual scanning for the semiconductor parts list (and looking for the 'special' Tek parts, I see designations on a number of diodes: Snap Diode, Check. No number of any sort.

I never heard of one of these so google is my friend....(aka snap off diode or charge-storage diode or memory varactor) studied the schematics of the pulse generator a bit and realized what a neat device and interesting circuit design.

It probably has a lot of bad parts, given the age, and while repair would be quite a learning experience, my basis questions a
1) how to determine the snap diode characteristics for this unique tek part?
2) and what are the chances of finding a reasonable substitute?

Assuming one of the snap diodes in the unit still functions, I could use a curve tracer and get some general parameters: Breakover voltage, approximate current range, reverse blocking voltage, leakage, etc. But determining the switch time would be critical in this application as that dictates the pulse characteristics.

Another thing that is of interest is this statement from Wikipedia:
"The main phenomenon used in SRDs is the storage of electric charge during forward conduction, which is present in all semiconductor junction diodes and is due to finite lifetime of minority carriers in semiconductors."
Finite lifetime of minority carriers....I assume when switching from forward conduction to reverse the minority carriers are quickly reversed in their flow given the abrupt change of voltage polarity?
J


Back then, TEK made many of their own diodes and transistors because
they could not get the quality and specs they wanted. They later made
their own ICs. We use one of their stencil machines today to screen
solder paste on PC boards.

Paul