Step Recovery Diodes - a blast from the past...

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A colleague drops by my office toating a Tek R293 Programmable pulse genera
tor and power supply and asks "Can I use a power supply?"  followed by, I h
aven'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 l
ooking for the 'special' Tek parts, I see designations on a number of diode
s: 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 circ
uit design.  

It probably has a lot of bad parts, given the age, and while repair would b
e quite a learning experience, my basis questions are:
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, approximat
e current range, reverse blocking voltage, leakage, etc.  But determining t
he switch time would be critical in this application as that dictates the p
ulse 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 a
nd is due to finite lifetime of minority carriers in semiconductors."
Finite lifetime of minority carriers....I assume when switching from forwar
d conduction to reverse the minority carriers are quickly reversed in their
 flow given the abrupt change of voltage polarity?  
J



Re: Step Recovery Diodes - a blast from the past...
On 2019/06/11 7:56 a.m., three_jeeps wrote:
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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 :-#)#

--  
(Please post followups or tech inquiries to the USENET newsgroup)
                      John's Jukes Ltd.
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Re: Step Recovery Diodes - a blast from the past...
wrote:

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"Prototype "Blue2" talking ESR meter"
<
https://www.youtube.com/watch?v=kYbsDlQ8nPg
(1:23)


It might be more useful it also announced if the capacitor was good,
marginal, or bad.  

There are some talking multimeters available, mostly for the blind.  
<http://www.mastrogippo.it/2014/03/a-talking-multimeter/
I played with one such home built meter that was built around a
Speak-and-Spell toy.
<https://en.wikipedia.org/wiki/Speak_%26_Spell_ (toy)>
I found the talking feature most useful when I couldn't read the
multimeter LED display in bright sunlight, such as working under the
hood of my car.  I don't think there's a need for a talking ESR meter
that works in bright sunlight.



--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Step Recovery Diodes - a blast from the past...
Jeff Liebermann wrote:

....................
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** Or, in Aussie parlance that would be:
  
  "beauty", "dodgy" and "fucked".



....  Phil  


Re: Step Recovery Diodes - a blast from the past...
On 2019/06/11 4:41 p.m., Jeff Liebermann wrote:
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I use an ESR meter for things besides caps, this chatty one that goes  
down to 0.001 ohms is handy for finding shorts between traces, and other  
jobs, not just testing caps. Maximum is around 90 ohms.

Bob's newest ESR project (He didn't think the talking meter would sell)  
is an EasyESR which has three LEDs and three different tones depending  
on the result. So there is your point, however the value of the cap is  
taken into consideration so the middle LED if on is good if under  
1000ufd but questionable if over 1000ufd.

Here is the prototype:


https://www.youtube.com/watch?v=o25gLeakcbM


Send him a note if you want it built!

John :-#)#
--  
(Please post followups or tech inquiries to the USENET newsgroup)
                      John's Jukes Ltd.
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Re: Step Recovery Diodes - a blast from the past...
wrote:

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Yet another idea.  Most supercaps have an extremely low ESR.  For
example, Murata claims 40 to 300 milliohms (measured at 1KHz).  
<https://www.murata.com/~/media/webrenewal/products/capacitor/edlc/techguide/electrical/c2m1cxs-053.ashx
Ask Bob Parker if he can build something to test those.  I have no
clue how to build probes with that low a contact resistance.  Fat
copper wires with silver contacts?  I don't have an immediate
application or market, but I keep running into supercaps with no way
to test them for anything more than capacitance.
--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Step Recovery Diodes - a blast from the past...
On 2019-06-12 18:05, Jeff Liebermann wrote:
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One would use Kelvin connections - probe resistance is not a major issue  
then.
https://en.wikipedia.org/wiki/Four-terminal_sensing

Arie

Re: Step Recovery Diodes - a blast from the past...
On 2019/06/12 12:50 p.m., Arie de Muynck wrote:
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her

 For
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hguide/electrical/c2m1cxs-053.ashx>  
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e  
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I forgot to mention that Bob uses Kelvin connections to his probes on  
the Talking ESR meter prototype.

John :-#)#


Re: Step Recovery Diodes - a blast from the past...
On Tue, 11 Jun 2019 08:15:05 -0700, John Robertson wrote:
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Just the thing for a blind repair tech!  :-)

Jonesy

Re: Step Recovery Diodes - a blast from the past...
On 6/11/19 10:56 AM, three_jeeps wrote:
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SRDs have been used for aeons.  Besides pulsers, as in the 20-ps-class  
Tek SD24 TDR sampling head, SRDs are used as high-order frequency  
multipliers.   You can still get them from Microsemi and maybe  
elsewhere--Arrow has 433 Microsemi GC2510 devices in stock.

One of my first engineering tasks back in 1981 was to rebias an X-band  
waveguide frequency multiplier using an SRD--we were changing from a  
Microwave Associates device to a Gigahertz Devices one.

The SRD was self-biased with a thick-film conductive ink drop on the  
side of the ceramic package.  I used a soft pencil to make the resistive  
shunt on the new device, and  varied it till I found the value that  
produced the highest efficiency.

The job was complicated by the tendency of the graphite to ablate. ;)

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Step Recovery Diodes - a blast from the past...
On Tue, 11 Jun 2019 07:56:08 -0700 (PDT), three_jeeps

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

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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.

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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?




--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Step Recovery Diodes - a blast from the past...
On Tuesday, June 11, 2019 at 9:03:43 PM UTC-4, Jeff Liebermann wrote:
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d be quite a learning experience, my basis questions are:
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art?  
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covery-diodes>
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I don't know if anything is wrong with this thing.  I have degrees in Elect
rical Computer engineering and focus on CPU architecture and hardware desig
n, and control theory.  As an EE, yea, designed/built lots of digital and a
nalog 'stuff' but never dabbled with microwave 'stuff' and the SRD was some
thing I've never come across till I was looking at the schematics and tech  
manual for this device.  Personally, I have no use for it and lots of other
 things to devote my time to, but I thought I'd ask some questions about th
ese devices on the off chance I'd do something with it.  
I did go down the route of looking up the tek cross to commercial parts and
 found nothing, so I am even more inclined not to deal with this thing. Giv
en that is vintage 1965 and hasn't been turned on in 30+ years, chances are
 components are non-functional.
Thanks for all the insights.
J

Re: Step Recovery Diodes - a blast from the past...
On 6/11/2019 7:56 AM, three_jeeps wrote:
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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

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