Date   

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


Re: Failed Transistor with Low h(FE)?

Chuck Harris <cfharris@...>
 

When tektronix said a part was selected, they didn't usually
share with us why.

I would expect that the listing meant the technician was to
try out transistors from the bin until one worked... for whatever
reason. That is a short sighted self defeating process, as the
bin will become more and more concentrated with parts that won't
work...

Back in the 1960's, when most of the small signal transistors
were originally designed, the processes were not as tightly
controlled as they are today. It was not unusual to get a
whole run of parts that didn't quite make the grade.

They sorted those different grade parts out, and gave them
different numbers, like the 2N3903/3904, example I gave in my
earlier post... though I think those are different voltage
capabilities.

Usually, when a part got an "A" version, that meant a process
change occurred. Often a reduction in process size, or maybe
an enhancement in some aspect of the design.

Selection of parts is a particular bugaboo of mine.

I generally buy resistors in bulk, thousands of a value at a
time, usually 5%. Occasionally, I need a 1% value and have
tried to select such a part our of my 5% parts. 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%.

Pretty unlikely unless someone at the factory beat me to all
of the 1% parts.

-Chuck Harris

Roy Thistle wrote:

On Thu, Feb 18, 2021 at 10:08 PM, Chuck Harris wrote:


tektronix didn't ascribe so much to this
philosophy, but still, they graded bins of common transistors
and gave them different part numbers based on different
parameters.

From the: Replaceable Electrical Parts-DM501
Q152 151-0192-00 TRANSISTOR: SILICON:NPN,SEL FROM MPS6521 80009 151-0192-00,

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.)

I don't see a 2N2907 in the DM501 parts list.
But there are some 2N2907A ... which indeed has a significantly higher Hfe than the 2N2907 (according to the Motorola small signal databk) ... and so since they came from the same Motorola process? ... was it Motorola binning parts, in this case?






Re: Help replacing a resistor/inductor in SG503

Tom Lee
 

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.

Sent from my iThing, so please forgive brevity and typos

On Feb 19, 2021, at 12:47, 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

Ed Breya
 

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: 93 Ohm feed-thru terminators - Unobtanium? No, as it turns out.

Milan Trcka
 

It is not recommended to plug 50 ohm N connector (central pin) into 75 ohm connector (central socket). The larger diameter 50 ohm pin will stretch the smaller diameter 75 ohm socket. This may (will) cause reliability of contact to degrade. This is important in precision test equipment such as network analyzers and similar. Opposite situation will not destroy the connector but may lead to reduced contact reliability all the same. HP manuals caution against mixing 50/75 ohm connectors.


Re: Failed Transistor with Low h(FE)?

Roy Thistle
 

On Thu, Feb 18, 2021 at 10:08 PM, Chuck Harris wrote:


tektronix didn't ascribe so much to this
philosophy, but still, they graded bins of common transistors
and gave them different part numbers based on different
parameters.
From the: Replaceable Electrical Parts-DM501
Q152 151-0192-00 TRANSISTOR: SILICON:NPN,SEL FROM MPS6521 80009 151-0192-00,

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.)

I don't see a 2N2907 in the DM501 parts list.
But there are some 2N2907A ... which indeed has a significantly higher Hfe than the 2N2907 (according to the Motorola small signal databk) ... and so since they came from the same Motorola process? ... was it Motorola binning parts, in this case?


Re: Help replacing a resistor/inductor in SG503

Dave Seiter
 

$10K just to pull a new part number???  I guess it depends on what it is and where/how it's used and how inefficient the documentation system is.  I've created complete documentation packages, including all the compliance related items in less than10 minutes.  OTOH, I recall parts at a few companies that easily cost that much (mostly due to silo culture and subsidiaries that didn't want to play ball).  At one place I worked, they routinely created part numbers for the babies of employees (as a joke, of course).
-Dave

On Friday, February 19, 2021, 07:43:33 AM PST, Dave Wise <david_wise@phoenix.com> wrote:

?We were strongly encouraged to use parts already in the Common Design Parts Catalog.  ISTR a new part number cost something like $10,000 in administrative overhead.y


Dave Wise

Information Display, 1980-1994?

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Tom Lee via groups.io <tomlee=ee.stanford.edu@groups.io>
Sent: Thursday, February 18, 2021 11:02 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help replacing a resistor/inductor in SG503

Hi John,

Your speculation might  be reasonable for LR142 vs LR150, although I
think that it is more likely that Tek used LR combos that were already
in inventory, rather than endure the paperwork in specifying a new part.
The resistance value isn't too critical for either LR142 or LR150. As
for LR190, though, its resistance actually matters: LR190 participates
in a series stack of parallel LR sections to produce a broadband
collector load resistance that is shunted at DC to keep the collector
swing about VCC. A single parallel LR wouldn't get the job done, owing
to the low self-resonant frequency of a 2.5mH choke. As the frequency
increases past the self-resonance of one section, another section cuts
in to keep the resistance high.

-- 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<http://www-smirc.stanford.edu>

On 2/18/2021 22:17, John Kolb wrote:

Looking at the schematic, there are a number of LR's and they are
wound on different value resistors. Noting that LR142 and LR150 are
both 0.25uH/51 ohms and LR135 and LR19? are both 2.5uH/2560 ohms, it
may be that Tek was only using the resistor value to identify the
component. Nevertheless you should duplicate the broken part as
exactly as possible. With the bad part intact except for the broken
lead, with even a cheap vernier caliper, you should be able to match
the part very well.

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 Oscillators LR140 Detail.jpg<https://groups.io/g/TekScopes/photo/260912/0/SG503 Oscillators LR140 Detail.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: Help replacing a resistor/inductor in SG503

Jared Cabot
 

And now resistors are ordered from Hi-Fi Collective.
I found they have a large stock of Allen Bradley resistors for a decent price and good shipping rates, so once they arrive, I'll be able to get some fine wire and wind some inductors while holding my tongue at the right angle to get them hopefully close to 20nH.....


Re: 93 Ohm feed-thru terminators - Unobtanium? No, as it turns out.

Glenn Little
 

In the 75 Ohm vs 50 Ohm world, the two are completely interchangeable as far as mating is concerned.
The 75 Ohm BNC connector is missing dielectric between the center pin and the shield.
Based on this I would suspect that this is the same with the 93 Ohm BNC connector.
But, I cannot guarantee this.
I have hear rumors that there was a difference in center pin as in the Type-N connector in early BNC connectors.
I have never seen this.
I have been working with radio for 50 plus years and am a retired TV chief engineer.
It was in the TV work that I saw the differences in connectors.
The clamp nut or crimp ferrule will be different in the different connectors.


Glenn

On 2/19/2021 9:35 AM, Dave Wright wrote:
Yes, I have a number of RG-62 with BNC jumpers, about a meter or so long, in my pile. Wondered what they could have been for... As I recall the BNCs mated OK with my 50 ohm stuff, but now I am inclined to look closer and see if there are dimensional differences...
Dave KC6UPS
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI, FRA, NRA-LM ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"


Re: Cleaning Scratchy Bourns MOD pots

John Griessen
 

On 2/19/21 1:22 AM, Ed Breya via groups.io wrote:
I think #14 or #12 solid wire is close enough in diameter to fill the corner holes, and stout enough to just fold over and hold the assembly together quite securely. I've done that before, on a temporary basis - ugly, but functional.
I love it! I have lots of 12 AWG 14 AWG for tying, mini rivets occasionally, better than baling wire, and now for pots it will hold tight when folded over and clamped/crimped some. Temporary-permanent is becoming a thing...for me at age 63 I'm less and less perfectionist.


Re: Cleaning Scratchy Bourns MOD pots

Renée
 

do be careful on bending the wire as it may break out a corner, usually upon removal when putting in the correct/ more correct screw..do not ask how I know...but it was eons ago on another project long forgotten but the lesson remained.
Renée

On 2/18/21 11:22 PM, Ed Breya via groups.io wrote:
Hi Dennis,

I don't recall how the Bourns pots look inside, but with the A-B ones, you almost can't go wrong. Once you figure out how they did the modular construction, you don't have to fear taking them apart and rebuilding - especially if you have others to salvage sub-parts from, even if they're not the in quite same arrangement. I've recently been building some multi-section A-B ones from a collection of others (most salvaged from Tek stuff), but have been stymied by not having quite the right items (special couplings) from single-section ones, to gang them together for multi-section use. If you're just doing a clean and rebuild, you don't have to worry about finding different pieces to modify them. The main thing is, don't break the original guts, and keep track of the them and the order of assembly. The screws or rivets to hold it all together are secondary.Actually, if worse comes to worse, you can use wire. I think #14 or #12 solid wire is close enough in diameter to fill the corner holes, and stout enough to just fold over and hold the assembly together quite securely. I've done that before, on a temporary basis - ugly, but functional.

Ed




Re: Help replacing a resistor/inductor in SG503

Jared Cabot
 

My next step is finding a 1/8W 47ohm carbon comp resistor or two... Tiny things, about 4mm long..

I don't think I'd even be able to find one in Akihabara here in Tokyo... seems 1/4W and up are far more common around the place.


Re: Help replacing a resistor/inductor in SG503

Dave Wise
 

?We were strongly encouraged to use parts already in the Common Design Parts Catalog. ISTR a new part number cost something like $10,000 in administrative overhead.


Dave Wise

Information Display, 1980-1994?

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Tom Lee via groups.io <tomlee=ee.stanford.edu@groups.io>
Sent: Thursday, February 18, 2021 11:02 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help replacing a resistor/inductor in SG503

Hi John,

Your speculation might be reasonable for LR142 vs LR150, although I
think that it is more likely that Tek used LR combos that were already
in inventory, rather than endure the paperwork in specifying a new part.
The resistance value isn't too critical for either LR142 or LR150. As
for LR190, though, its resistance actually matters: LR190 participates
in a series stack of parallel LR sections to produce a broadband
collector load resistance that is shunted at DC to keep the collector
swing about VCC. A single parallel LR wouldn't get the job done, owing
to the low self-resonant frequency of a 2.5mH choke. As the frequency
increases past the self-resonance of one section, another section cuts
in to keep the resistance high.

-- 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<http://www-smirc.stanford.edu>

On 2/18/2021 22:17, John Kolb wrote:

Looking at the schematic, there are a number of LR's and they are
wound on different value resistors. Noting that LR142 and LR150 are
both 0.25uH/51 ohms and LR135 and LR19? are both 2.5uH/2560 ohms, it
may be that Tek was only using the resistor value to identify the
component. Nevertheless you should duplicate the broken part as
exactly as possible. With the bad part intact except for the broken
lead, with even a cheap vernier caliper, you should be able to match
the part very well.

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 Oscillators LR140 Detail.jpg<https://groups.io/g/TekScopes/photo/260912/0/SG503 Oscillators LR140 Detail.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: 93 Ohm feed-thru terminators - Unobtanium? No, as it turns out.

Dave Wright
 

Yes, I have a number of RG-62 with BNC jumpers, about a meter or so long, in my pile. Wondered what they could have been for... As I recall the BNCs mated OK with my 50 ohm stuff, but now I am inclined to look closer and see if there are dimensional differences...

Dave KC6UPS


Re: Failed Transistor with Low h(FE)?

 

Dennis, Chuck, et-al,

thank you for the input and elucidation, it has been quite helpful. Unfortunately it appears that my display board, not the transistors that drive the select lines, that is the damaged component, and the damage affects all three low order digits.

-- Jeff Dutky


Re: Cleaning Scratchy Bourns MOD pots

Ed Breya
 

Hi Dennis,

I don't recall how the Bourns pots look inside, but with the A-B ones, you almost can't go wrong. Once you figure out how they did the modular construction, you don't have to fear taking them apart and rebuilding - especially if you have others to salvage sub-parts from, even if they're not the in quite same arrangement. I've recently been building some multi-section A-B ones from a collection of others (most salvaged from Tek stuff), but have been stymied by not having quite the right items (special couplings) from single-section ones, to gang them together for multi-section use. If you're just doing a clean and rebuild, you don't have to worry about finding different pieces to modify them. The main thing is, don't break the original guts, and keep track of the them and the order of assembly. The screws or rivets to hold it all together are secondary.Actually, if worse comes to worse, you can use wire. I think #14 or #12 solid wire is close enough in diameter to fill the corner holes, and stout enough to just fold over and hold the assembly together quite securely. I've done that before, on a temporary basis - ugly, but functional.

Ed


Re: Help replacing a resistor/inductor in SG503

Tom Lee
 

Hi John,

Your speculation might  be reasonable for LR142 vs LR150, although I think that it is more likely that Tek used LR combos that were already in inventory, rather than endure the paperwork in specifying a new part. The resistance value isn't too critical for either LR142 or LR150. As for LR190, though, its resistance actually matters: LR190 participates in a series stack of parallel LR sections to produce a broadband collector load resistance that is shunted at DC to keep the collector swing about VCC. A single parallel LR wouldn't get the job done, owing to the low self-resonant frequency of a 2.5mH choke. As the frequency increases past the self-resonance of one section, another section cuts in to keep the resistance high.

-- 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 2/18/2021 22:17, John Kolb wrote:

Looking at the schematic, there are a number of LR's and they are wound on different value resistors. Noting that LR142 and LR150 are both 0.25uH/51 ohms and LR135 and LR19? are both 2.5uH/2560 ohms, it may be that Tek was only using the resistor value to identify the component. Nevertheless you should duplicate the broken part as exactly as possible. With the bad part intact except for the broken lead, with even a cheap vernier caliper, you should be able to match the part very well.

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: Help replacing a resistor/inductor in SG503

John Kolb
 

Looking at the schematic, there are a number of LR's and they are wound on different value resistors. Noting that LR142 and LR150 are both 0.25uH/51 ohms and LR135 and LR19? are both 2.5uH/2560 ohms, it may be that Tek was only using the resistor value to identify the component. Nevertheless you should duplicate the broken part as exactly as possible. With the bad part intact except for the broken lead, with even a cheap vernier caliper, you should be able to match the part very well.

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!

14321 - 14340 of 193046