1. Home
  2. Electronics Repair
  3. Step Recovery Diodes - a blast from the past...

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

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

Reply to
three_jeeps
Loading thread data ...

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:

formatting link

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup) 
                      John's Jukes Ltd. 
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 
          (604)872-5757 (Pinballs, Jukes, Video Games) 
                      www.flippers.com 
        "Old pinballers never die, they just flip out."
Reply to
John Robertson

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 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

"Prototype "Blue2" talking ESR meter" (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. I played with one such home built meter that was built around a Speak-and-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     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

....................

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

.... Phil

Reply to
Phil Allison

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:

formatting link

Send him a note if you want it built!

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup) 
                      John's Jukes Ltd. 
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 
          (604)872-5757 (Pinballs, Jukes, Video Games) 
                      www.flippers.com 
        "Old pinballers never die, they just flip out."
Reply to
John Robertson

Just the thing for a blind repair tech! :-)

Jonesy

Reply to
Allodoxaphobia

Which diodes are you referring to? I checked the R293 manual at: 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.

I don't know. Start digging: Maybe more here:

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: etc. You probably don't need rise times suitable for generating microwave frequencies.

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     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

Yet another idea. Most supercaps have an extremely low ESR. For example, Murata claims 40 to 300 milliohms (measured at 1KHz). 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     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

d be quite a learning experience, my basis questions are:

art?

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

Reply to
three_jeeps

One would use Kelvin connections - probe resistance is not a major issue then.

formatting link

Arie

Reply to
Arie de Muynck

her

For

o

e

I forgot to mention that Bob uses Kelvin connections to his probes on the Talking ESR meter prototype.

John :-#)#

Reply to
John Robertson

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

Reply to
Paul Drahn

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.