On 2019/06/11 7:56 a.m., 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
Not sure about the Snap Diodes - you might want to check archive.org or
bitsaver.org for the Master Electronics Catalogs from that time for
specs. Sound like fast recovery diodes to me...
However in most cases running an ESR meter (Like Bob Parker's Blue ESR
meter kit) over the various capacitors will find a few bad ones at which
point the power supply may well work. Caps and electrical connections
are the weak link in electronics...
Just was playing with one of Bob's latest prototype ESR meter designs
yesterday which is a talking ESR meter and working on a sound board with
low volume. Having the meter talk to me (Bob's voice) was handy in that
I didn't have to take my eyes off the job and things went very quickly.
The meter going down to 0.001 ohms is handy too...
Nag Bob if you want to see these in production, he isn't sure there is a
market for a talking ESR meter...
He is currently working on this version of a simple ESR meter kit:
https://www.youtube.com/watch?v=o25gLeakcbM
John :-#)#
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