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Old June 12th 19, 02:03 AM posted to sci.electronics.repair
Jeff Liebermann Jeff Liebermann is offline
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Default Step Recovery Diodes - a blast from the past...

On Tue, 11 Jun 2019 07:56:08 -0700 (PDT), three_jeeps
wrote:

I never heard of one of these so google is my friend....(aka snap
off diode or charge-storage diode or memory varactor)


Which diodes are you referring to? I checked the R293 manual at:
http://w140.com/tekwiki/wiki/R293
http://w140.com/tek_r293.pdf
In the description, it refers to "avalanche diodes". In the parts
list, they are "Snap off, Checked" whatever that means.
D224, D240, D274, and D290.
http://w140.com/tekwiki/wiki/Step_recovery_diode

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?


I don't know. Start digging:
http://w140.com/tek_xref_free.pdf
http://w140.com/Tek_RPR_152-_Diodes.pdf
Maybe more he
http://w140.com/tekwiki/wiki/Reference_material

2) and what are the chances of finding a reasonable substitute?


Marginal. Finding an exact replacement, impossible.

The TEK part number in the manual for these "snap" diodes is
153-0023-00. Google doesn't seem to find anything. The Tek to vendor
cross reference lists the part number as a "selected part" and "Sig,
Snap off" with a vendor number of "Ref. only". That's not very useful
information. This rather smells of bin selected parts in matched
pairs, which is going to be difficult to substitute without know what
parameters are being matched.

When you remove the diodes for testing in the R293, be sure to mark
them with their original Rxxx reference designator so that the return
to the same location on the PCB.

Looks like some of the microwave semiconductor houses still make step
recovery diodes for use in comb generators, frequency multipliers,
sub-harmonic generators, and maybe pulse generators:
https://www.microsemi.com/product-directory/varactor-diodes/3150-step-recovery-diodes
https://www.macom.com/products/diodes/multiplier-step-recovery-diodes
https://www.semigen.net/step-recovery-diodes/
http://www.advancedsemiconductor.com/diodes/step_recovery.shtml
etc. You probably don't need rise times suitable for generating
microwave frequencies.

Assuming one of the snap diodes in the unit still functions, I
could use a curve tracer and get some general parameters...


Are you sure that there's something wrong with the original step
recovery diodes? They might all be good and no replacement is needed.
Maybe ask the same questions in one of the Tek specific Yahoo Groups?




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