Date   

Re: 1L10 crystal needed (Newbie)

Kerry Burns
 

Hello Joel



Its probably worth trying the Czech company Krystaly – if you haven’t done so already.   Their website is http://www.krystaly.cz/en/

I have previously obtained a small batch of crystals from them and they were good to deal with and not too expensive.



Regards



Kerry



From: <TekScopes@groups.io> on behalf of Joel B Walker <joelandjoyce@esinc.net>
Reply to: <TekScopes@groups.io>
Date: Saturday, 20 February 2021 at 3:21 pm
To: <TekScopes@groups.io>
Subject: Re: [TekScopes] 1L10 crystal needed (Newbie)



Yes that was me. No luck there either. I ran a classified ad there and got several replies about both crystals, but no one had any. One member offered to sell me his 1L10 but wanted too much for it. And even if I had bought it I would still be looking for crystals for mine. Surely there is ONE 900.000 kHz out there somewhere.


Re: Help replacing a resistor/inductor in SG503

Tom Lee
 

Nice job, Tom. Sounds like a bit of work, but once you made the jig, I guess you were able to crank these out.

And yes, those LRs are indeed noise filters. Without the shunt L, there would be a dc drop across the resistor. The shunt L eliminates the drop, but above the R/L frequency (here, about 500kHz), the combo looks pretty much just like the plain old R.

--Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 2/19/2021 16:02, TomC wrote:
The 7A26 has 4 such LR components: LR1010, LR1014, LR1020, LR1024. They are 3.2uH wound on 10 ohm carbon comp. resistors. They are on the + and - 15 volt lines and are probably filtering noise going to the A2 board.

They feed 10 uf tantalums which when they go short burn up the LR components and produce a tremendous amount of smoke.

To fix, I took a closeup photo of one that hadn't been damaged and counted turns. There are 47 turns. Found the wire gauge with a micrometer on the wire from one that was destroyed. Then ordered wire and a supply of carbon comp 10 ohm resistors.

Made up a jig to wind the 47 turns on new 10 ohm resistors. Then soldered the ends and painted with dope.

Tom


On 2/18/2021 8:30 AM, Jared Cabot via groups.io wrote:
Hi all,
I recently got myself an SG503 Leveled Sine Wave generator for a good price and I am currently repairing it back to operational condition.

I found a few components in the oscillator section were damaged, from what I guess, is from some ham-fisted poking from someone's previous repair attempt.
Most parts were easy to replace, but I'm a bit stuck on one. LR140 is a 20nH inductor consisting of a couple turns of fine wire around a 1/8w 47ohm carbon composite resistor.
It looks like it has been poked at and one leg was broken off.
Below is linked a page from the schematics with the part highlighted in red.
https://groups.io/g/TekScopes/photo/260912/0/SG503%20Oscillators%20LR140%20Detail.jpg

My question is, How's the best way to recreate this sort of part? I tried winding a few turns on a 1/8 metal film resistor and didn't have much luck, I have a DE-5000 LCR meter and a HP 4276A etc but it's a little difficult to measure such small values reliably.
Should I get a carbon composite resistor from Digikey/Mouser to recreate the part more true to the original design instead of the metal film I used? Or is a plain 20nH axial inductor without the resistor ok to use? Any other ideas or suggestions?

Thanks!







Re: Cleaning Scratchy Bourns MOD pots

Michael A. Terrell
 

Dennis Tillman W7pF wrote:
Hi Ed,
I never thought about suction until you just mentioned it just now. Thank you for that intriguing new strategy for cleaning these sealed pots.

One idea I had (with no success) was to immerse the dual-pot/pull-switch assembly in cleaning solution in an ultrasonic cleaner. My hope was the ultrasonic bursting bubbles would be able to get some solution into the wipers through the shafts. I left the dual-pot/pull-switch assembly in the ultrasonic cleaner for a few hours to give it every chance to succeed. It had absolutely no effect :(

I did consider removing the rivets but decided against it since I was sure nobody sold 1 1/2" 2-56 screws. Reading your email made me realize that was a stupid assumption. McMaster-Carr sells 2-56 screws up to 1 3/4" long at very reasonable prices ($7 for 25 screws). There are even longer ones but they cost much more.

The particular dual-pot/pull-switch I desperately need to clean is the one that controls the output level and DC offset of an otherwise pristine late model FG 501A function generator. This is a very impressive plugin capable of 30Vp-p into 50 ohms from 0.2milliHz to several MHz. I would REALLY like to be able to adjust the DC offset (which goes from +15V to -15V) so I could set the square wave output to go from 0V to +30V into 50 ohms. That is more than 1/2A output!!!

My concern now is that if I remove ALL of the rivets I will have a very difficult time getting it all back together. Do you think I would be able to get cleaning solution into the assembly if I drilled out two of the rivets on opposite corners of the assembly?

I suppose if I was going to go that far it would be better to drill out one rivet at a time and replace it with a screw loosely tightened on the assembly. Once all 4 rivets were replaced with loosely tightened screws this way there should be sufficient room for cleaning solution to get in without altering the alignment and arrangement of the internal parts.

I think I just answered my own question. But once again I could not have done it without your help.
I'm ordering the 1/1/2" 2-56 screws I need from McMaster-Carr right now.

Microdyne used Accurate Screw Machine Company for electronics type hardware for our products. They have a very wide array of stock items, and can make special hardware for production runs. screws start on page 113. Some on the group my find it useful for items they build to sell and need quantities of oddball hardware. I have included a link to their catalog:

<https://dpk3n3gg92jwt.cloudfront.net/domains/asm/pdf/Accurate_Screw_Machine_Catalog.pdf>


Fastenal has them. I don't know about your area, but I have four branches near me or you can buy online. :

<https://www.fastenal.com/product/fasteners/screws/machine-screws/600059?categoryId=600059&level=3&isExpanded=true&Length=1-1/2%22&Dia/Thread%20Size=%232-56&showAll=Length&productFamilyId=21356>


Re: 1L10 crystal needed (Newbie)

Joel B Walker
 

Yes that was me. No luck there either. I ran a classified ad there and got several replies about both crystals, but no one had any. One member offered to sell me his 1L10 but wanted too much for it. And even if I had bought it I would still be looking for crystals for mine. Surely there is ONE 900.000 kHz out there somewhere.


Re: Help replacing a resistor/inductor in SG503

Harvey White
 

GIven that the recommendation of the manufacturers was to minimize the headroom between the working voltage and the rated voltage (to the point where things fail.....)

That's a good idea to replace with higher voltage ratings, but I'm dumping this in here in case someone only hits this thread and doesn't research the older (and similar) ones.

but I can't figure out how to shoehorn FOOM! in here.....

Harvey

On 2/19/2021 9:37 PM, TomC wrote:


On 2/19/2021 5:57 PM, Roy Thistle wrote:
On Fri, Feb 19, 2021 at 04:02 PM, TomC wrote:


To fix, I took a closeup photo of one that hadn't been damaged and counted
turns. There are 47 turns. Found the wire gauge with a micrometer on the wire
from one that was destroyed. Then ordered wire and a supply of carbon comp 10
ohm resistors.

Made up a jig to wind the 47 turns on new 10 ohm resistors. Then soldered the
ends and painted with dope.
As Stan Lee would say, "nuff said!"
Actually, what I failed to say was that I replaced those 4 tantalums, using a higher voltage rating, in every 7A26 I own. Both the ones that had failed short, and the ones that hadn't failed yet.  But that is probably obvious to the people here.






Re: Help replacing a resistor/inductor in SG503

TomC
 

On 2/19/2021 5:57 PM, Roy Thistle wrote:
On Fri, Feb 19, 2021 at 04:02 PM, TomC wrote:


To fix, I took a closeup photo of one that hadn't been damaged and counted
turns. There are 47 turns. Found the wire gauge with a micrometer on the wire
from one that was destroyed. Then ordered wire and a supply of carbon comp 10
ohm resistors.

Made up a jig to wind the 47 turns on new 10 ohm resistors. Then soldered the
ends and painted with dope.
As Stan Lee would say, "nuff said!"
Actually, what I failed to say was that I replaced those 4 tantalums, using a higher voltage rating, in every 7A26 I own. Both the ones that had failed short, and the ones that hadn't failed yet. But that is probably obvious to the people here.


Re: Help replacing a resistor/inductor in SG503

Roy Thistle
 

On Fri, Feb 19, 2021 at 04:02 PM, TomC wrote:


To fix, I took a closeup photo of one that hadn't been damaged and counted
turns. There are 47 turns. Found the wire gauge with a micrometer on the wire
from one that was destroyed. Then ordered wire and a supply of carbon comp 10
ohm resistors.

Made up a jig to wind the 47 turns on new 10 ohm resistors. Then soldered the
ends and painted with dope.
As Stan Lee would say, "nuff said!"


Re: 1L10 crystal needed (Newbie)

Roy Thistle
 

Hi Joel:
I thought I'd seen something about 49.3 MHz crystal before.
Was it you on Antique radios, almost 8 years ago, and hundreds of crystals later?


Re: International Orders for Peter Keller's book were MAILED TODAY

 

Hi Dennis, didn't see this until now. I think the book might be lost
in transit - unfortunately it went through the UK and post Brexit a
lot of stuff just plain got lost in the mail unfortunately. Any way
you can request the courier looks into this? Either way sending over
the shipment that is due.

On Fri, Jan 8, 2021 at 6:24 AM Dennis Tillman W7pF <dennis@ridesoft.com> wrote:

I mailed all of the international orders for Peter Keller's book today with
the exception of the five going in one package to the United Kingdom via
UPS. Those will be mailed as soon as I get the paperwork.

I underestimated the shipping on all of your books by a few dollars. I
suspect this was because I did not yet have the corrugated mailer boxes when
the post office window clerk weighed the book and estimated what your
postage would be. If you would be so kind to send me the additional postage
I would appreciate it.

Listed alphabetically according to country. For privacy this only contains
your initials with your country, your tracking number, the estimated postage
you sent me, the actual postage I paid today, and the difference.
EP, AUSTRALIA, Tracking #: LH127121053US, Estimated Postage: $37.00, Actual
Postage: $43.00, POSTAGE DUE: $6.00
RL, AUSTRALIA, Tracking #: LH127121739US, Estimated Postage: $37.00, Actual
Postage: $43.00, POSTAGE DUE: $6.00
DM, AUSTRIA, Tracking #: UH032260245US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
VK, BULGARIA, Tracking #: UH032260452US, Estimated Postage: $37.00, Actual
Postage: $40.50, POSTAGE DUE: $3.50
AG, CANADA, Tracking #: LH127124103US, Estimated Postage: $28.00, Actual
Postage: $32.00, POSTAGE DUE: $4.00
DJ, CANADA, Tracking #: LH127125165US, Estimated Postage: $28.00, Actual
Postage: $32.00, POSTAGE DUE: $4.00
SM, CANADA, Tracking #: LH127125982US, Estimated Postage: $28.00, Actual
Postage: $32.00, POSTAGE DUE: $4.00
SA, CANADA, Tracking #: LH127126740US, Estimated Postage: $28.00, Actual
Postage: $32.00, POSTAGE DUE: $4.00
DG, CANADA, Tracking #: LH127128207US, Estimated Postage: $28.00, Actual
Postage: $32.00, POSTAGE DUE: $4.00
SS, FRANCE, Tracking #: LH127128895US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
SJ, FRANCE, Tracking #: LH127129777US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
CB, GERMANY, Tracking #: LH127130378US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
HB, GERMANY, Tracking #: LH127131339US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
JW, GERMANY, Tracking #: LH127132087US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
AV, ITALY, Tracking #: UH032263312US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
DG, ITALY, Tracking #: UH032263493US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
MG, ITALY, Tracking #: UH032263670US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
JC, JAPAN, Tracking #: LH127134834US, Estimated Postage: $37.00, Actual
Postage: $43.00, POSTAGE DUE: $6.00
LP, NETHERLANDS, Tracking #: LH127136027US, Estimated Postage: $37.00,
Actual Postage: $39.00, POSTAGE DUE: $2.00
RD, NETHERLANDS, Tracking #: LH127137186US, Estimated Postage: $37.00,
Actual Postage: $39.00, POSTAGE DUE: $2.00
TK, NORWAY, Tracking #: UH032264180US, Estimated Postage: $37.00, Actual
Postage: $39.00, POSTAGE DUE: $2.00
GL, SINGAPORE, Tracking #: LH127138120US, Estimated Postage: $37.00, Actual
Postage: $40.50, POSTAGE DUE: $3.50
JW, UNITED KINGDOM, Tracking #: LH127138986US, Estimated Postage: $37.00,
Actual Postage: $39.00, POSTAGE DUE: $2.00
PS, UNITED KINGDOM, Tracking #: LH127119647US, Estimated Postage: $37.00,
Actual Postage: $39.00, POSTAGE DUE: $2.00

Apologies to Esmond Pitt: Moments before the post office clerk printed my
receipt today he surprised me by asking if I wanted it emailed, printed, or
both. If I had known that last week I would have been able to include
tracking numbers for all the books going to the US in the email I sent to
TekScopes last Saturday.

Dennis Tillman W7pF







Re: Failed Transistor with Low h(FE)?

shalopt
 

Yes and that is how you get the 10% values, two piles none will be with in the 5%, and a long while back the
+- 20%. It has always been this way. I have found if I buy a batch they will all be on either the + or - side but not both, seldom both sides. That old bell curve in play.


Re: Help replacing a resistor/inductor in SG503

TomC
 

The 7A26 has 4 such LR components: LR1010, LR1014, LR1020, LR1024. They are 3.2uH wound on 10 ohm carbon comp. resistors. They are on the + and - 15 volt lines and are probably filtering noise going to the A2 board.

They feed 10 uf tantalums which when they go short burn up the LR components and produce a tremendous amount of smoke.

To fix, I took a closeup photo of one that hadn't been damaged and counted turns. There are 47 turns. Found the wire gauge with a micrometer on the wire from one that was destroyed. Then ordered wire and a supply of carbon comp 10 ohm resistors.

Made up a jig to wind the 47 turns on new 10 ohm resistors. Then soldered the ends and painted with dope.

Tom

On 2/18/2021 8:30 AM, Jared Cabot via groups.io wrote:
Hi all,
I recently got myself an SG503 Leveled Sine Wave generator for a good price and I am currently repairing it back to operational condition.
I found a few components in the oscillator section were damaged, from what I guess, is from some ham-fisted poking from someone's previous repair attempt.
Most parts were easy to replace, but I'm a bit stuck on one. LR140 is a 20nH inductor consisting of a couple turns of fine wire around a 1/8w 47ohm carbon composite resistor.
It looks like it has been poked at and one leg was broken off.
Below is linked a page from the schematics with the part highlighted in red.
https://groups.io/g/TekScopes/photo/260912/0/SG503%20Oscillators%20LR140%20Detail.jpg
My question is, How's the best way to recreate this sort of part? I tried winding a few turns on a 1/8 metal film resistor and didn't have much luck, I have a DE-5000 LCR meter and a HP 4276A etc but it's a little difficult to measure such small values reliably.
Should I get a carbon composite resistor from Digikey/Mouser to recreate the part more true to the original design instead of the metal film I used? Or is a plain 20nH axial inductor without the resistor ok to use? Any other ideas or suggestions?
Thanks!


Re: Shipped They Are

Roy Thistle
 

On Fri, Feb 19, 2021 at 06:50 AM, Michael W. Lynch wrote:


just an observation
Chamfer isn't in Eagle (et. al.)... usually, PCB design packages, just have just drilling and routing (Chamfering is mechanical design).
Chamfering edge connectors is usually a 'full-featured' custom PCB quote... as is gold plating on edge connectors (though some Asian fabs now routinely have drop down boxes for gold plating, on their Webquote pages): chamfering and plating always used to be fab notes.
Even though several people (whom I consider to be experts) have said (I think) that chamfering doesn't matter for TM500 insertions... chamfered edge connectors have been an IPC standard, probably, for the better part of 5 decades.
I'd be surprised if Tektronix didn't follow that, and the manufacturers of the edge connectors that Tektronix used in TM500 designs didn't call for it too.


Re: 1L10 crystal needed (Newbie)

Joel B Walker
 

Hello all,
Since posting here last I have tried a few places. Quartslab, which is in Great Britain, advertised that they will make custom one-off crystals, and the price list they showed seemed reasonable. There was a guy named Dave that I corresponded with. He was very helpful. The normal range of frequencies they deal with bottoms out at 1.5 MHz. He stated they could make me one anyway for about $100.00 including shipping as an estimate. That was a lot, but I said go ahead and do an official quote. Well, the quote ended up being $195.00!! Not worth it. The other place that specialized in low frequency crystals never responded to 4 emails from me. I contacted Walter Shawlee of Sphere and he didn't have the 900 kHz one, but he DID have a new Tektronix 49.3 MHz crystal for $5, which I ordered. Thanks, Walter! So I'll ask again, PLEASE look in all y'all's junk boxes or where ever and find me a 900 kHz crystal. Thanks.


Re: Help replacing a resistor/inductor in SG503

Dave Seiter
 

I've been in many, many meetings where the merits of various part number systems have been argued.  I personally prefer a smart system, so you can tell more or less what an item is without seeing a description, but it's easy to run out of options, especially for resistors if it's not designed carefully.  One company I worked for ran out of prefixes (the original format was xx-xxxxx), and they up adding a 4 digit suffix to everything, most of which was just "-0000".  It was a mess because they decided to suppress the suffix unless it was needed. The assembly houses hated it!
The worst component engineering fiasco I ever had to deal with was a client that had been through a string of CEs, then given up and made the buyers wear the CE hat for their commodities.  That only made things worse, and I spent months recreating the documentation for every part, along with verifying part numbers, usage, etc. (All hard copy)
-Dave

On Friday, February 19, 2021, 01:55:05 PM PST, Michael A. Terrell <terrell.michael.a@gmail.com> wrote:

Tom Lee wrote:
And we mustn’t forget that database and documentation technology in 1975 (or whenever it was that the SG503 debuted) involved much more manual labor than today’s technology. “I just want to add a new part” triggers a cascade of activity that puts an avalanche sampling switch to shame.
I was interviewed for component engineer at my last company. The head of
engineering wanted a whole new part number system. for resistors, he
wanted to use the resistance . He got mad when I pointed out that we had
over 30 different 10Kohm resistors in inventory He also didn't like my
idea of assigning a block of numbers for an entire series, with the
unused values marked as reserved for future use, Our MRP/Inventory
software could flag and not display these numbers, but keep values and
series grouped together. In the end, I didn't get the job, because I had
no college degree. He hired a woman with a Philosophy degree who threw
out over 1000 data books to give her a bigger office. Then she had the
nerve to ask me to create item masters and do failure analysis for her.
I told her no, so she would just photocopy a catalog page and scribble a
part number on it. Sometimes she even underlined the actual part. No
datasheet, or having a component qualified. She didn't last long, then
he was fired but not until they left a hell of a mess for others to
clean up. I had about 75 older data books at my workbench, to track down
long term manufacturing problems that had been ignored. Some were really
stupid things, like the prototype used an NMOS MPU, but by the time it
was in production, only CMOS were available and no one changed the pair
of capacitors on the time base crystal. Even though I was assigned to
production, I got a lot of work from Engineering about component
problems. Some that shut down a product line. They knew that I wouldn't
put up with any BS from any department, and that I never failed to solve
the problems.


Re: Failed Transistor with Low h(FE)?

Roy Thistle
 

On Thu, Feb 18, 2021 at 07:56 AM, Jeff Dutky wrote:


I was expected to find the failed part as a short or open. Could a failed
transistor simply have a decreased gain?
If the design is pushing the transistor into saturation... to make sure switching occurs under different operating conditions... then since under saturation, the beta drops to a fraction. Then yes... since a minimum beta is usually assumed, for reliable switch design. And if the beta of the "failed" transistor is less than (or around) that assumed minimum, there could be problems.
It's interesting to note... that research shows silicon epitaxial transistors do start to diminish in performance, with age and with operation. The thin silicon layer between the base and emitter, tends to degrade with time or operation.


Re: Help replacing a resistor/inductor in SG503

Roy Thistle
 


If you can't obtain exactly the same gauge wire wound to the exact same pitch, don't worry.
Well... if one uses too small a gauge wire... then, one might be winding a slo-blow fuse (or a fast-blow).
If one understands why Tek added this "choke" to the circuit (and, I'm not saying people don't)... then ...
But, then how hard can it be to "duplicate" a simple part, like this?


Re: Help replacing a resistor/inductor in SG503

Dave Seiter
 

I guess it depends on the type of part.  At most companies, we strictly dealt with OTS items, which have a much lower initial cost than custom fabrications.  OTOH, even custom parts, long established, can be handful.  My worst case story was a small rf module (I forget exactly what it was, maybe a notch filter) that we purchased from a small company on the east coast that did mostly military work.  My company had been buying these things on and off for years, but never more than about 4-5 per year (they were used on an assembly that was a rarely sold option).  After spending years gathering full substance-level compliance data for 66K parts, this item was on my short list of "problems"- we couldn't even get a generic RoHS declaration for it.  It became a VP level issue, but the manufacturer refused to spend time on a part we *maybe* spent $500/year on.  Since we purchased so few, it made no sense to farm it out to another company (I'm not sure we could have anyway, I think the company we bought it from had designed it for us)  I ended up doing a tear down and XRFing the pieces just to ensure nothing too nasty was going on.  
-Dave

On Friday, February 19, 2021, 12:47:51 PM PST, Ed Breya via groups.io <edbreya=yahoo.com@groups.io> wrote:

Dave wrote: "$10K just to pull a new part number???"

That's way on the low side, when you consider the overhead, to administer a part number, and the physical logistics involved, for a very long time - possibly decades. So yes, the processing of a single PPIF (Purchased Part Initiation Form) didn't take much up front - it's what comes afterward that counts. Just think about what happens when everyone else gets involved, to make it a reality. It ripples through the entire business process - purchasing, quality control, documentation, inventory control, distribution, and so on - so you can grab one from a bin and stick it in a circuit. New parts are essential, in order to use newer and better technologies, or where nothing else will do. I did a few PPIFs in my day, but never for common items for which there were easy to find, similar, existing part numbers. You can often tweak the design anyway, to accommodate what's available, rather than demanding a new part just to make it work.

When I was in MBA school, I learned of a fairly new (at the time) approach to really figuring out how much things cost in overhead. I totally "got" it, and was zealous about it, and considered it when applicable, in all financial and cost analysis I did. It goes way beyond just managing parts, to pretty much anything.

Just like in designing electronics or anything else, if you can't measure it, you can't improve it. This method is called "Activity-Based Costing" or something like that. It is now well known and used extensively. You can look it up and see the principles and processes involved. I think the professor of that accounting class may have written one of the many books on the subject. I can't remember for sure, but vaguely recall something about it.

Ed


Re: Help replacing a resistor/inductor in SG503

Michael A. Terrell
 

Tom Lee wrote:
And we mustn’t forget that database and documentation technology in 1975 (or whenever it was that the SG503 debuted) involved much more manual labor than today’s technology. “I just want to add a new part” triggers a cascade of activity that puts an avalanche sampling switch to shame.
I was interviewed for component engineer at my last company. The head of engineering wanted a whole new part number system. for resistors, he wanted to use the resistance . He got mad when I pointed out that we had over 30 different 10Kohm resistors in inventory He also didn't like my idea of assigning a block of numbers for an entire series, with the unused values marked as reserved for future use, Our MRP/Inventory software could flag and not display these numbers, but keep values and series grouped together. In the end, I didn't get the job, because I had no college degree. He hired a woman with a Philosophy degree who threw out over 1000 data books to give her a bigger office. Then she had the nerve to ask me to create item masters and do failure analysis for her. I told her no, so she would just photocopy a catalog page and scribble a part number on it. Sometimes she even underlined the actual part. No datasheet, or having a component qualified. She didn't last long, then he was fired but not until they left a hell of a mess for others to clean up. I had about 75 older data books at my workbench, to track down long term manufacturing problems that had been ignored. Some were really stupid things, like the prototype used an NMOS MPU, but by the time it was in production, only CMOS were available and no one changed the pair of capacitors on the time base crystal. Even though I was assigned to production, I got a lot of work from Engineering about component problems. Some that shut down a product line. They knew that I wouldn't put up with any BS from any department, and that I never failed to solve the problems.


Re: Failed Transistor with Low h(FE)?

Siggi
 

On Fri, Feb 19, 2021 at 2:26 PM Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

This says for Q153, "SEL FROM MPS6521," ... which means to me ... select
the "right" MPS6521, from a pile of MPS6521.
The MPS6521 had a maximum Hfe of 600 (according to the Fairchild Discrete
databk) ... so did/could that mean that Tektronix sorted the MPS6521 they
got from Fairchild? ... for, the best gain? ( It's 80009, or a Tek part.)
If you look on page 6-4 of the Common Parts Catalog, I believe it gives you
the selection criteria. I think hFE_MIN = 300 is possibly the most salient
selection criteria for this part.
Note that there are also 151-0192-01 etc parts in the catalog. Perhaps
those were selected for the same criteria?


Re: Failed Transistor with Low h(FE)?

Ed Breya
 

Chuck wrote: " What I generally
find is that out of 1000's of 5% resistors, not a single one
was within 1% of its nominal value. But, all were within 5%."

These two-lobed distributions are common. The ones that fell in the middle range near 1% were likely separated out and sold as a better grade part, leaving the rest of the distribution (which should be normal) with a hole in the middle.

Ed

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