Date   

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!


Re: Help replacing a resistor/inductor in SG503

Jared Cabot
 

Hi all,
The resistor in question is definitely 47ohm, I was able to read the colour code on the resistor, so I assume it is required for damping or the like instead of just a former.
I think I'll try to replicate the original part as close as possible to avoid chasing my tail.

I wonder if lower value resistors in this application are critical enough that the usual carbon comp resistor value drift is a concern? Should I look at the other inductors of this construction type or avoid poking the bear? There are 5 or so of varying values around the place.


Re: Failed Transistor with Low h(FE)?

Chuck Harris <cfharris@...>
 

On hfe and other transistor parameters:

What Dennis says is 100% true. But there is a little
something that you must remember for early manufacture,
and early uses of transistors: They were very, very
expensive! I can remember paying $20 each for some of
the early silicon transistors in the 1960's.... Gas was
$0.20/gallon back then, to give you some perspective...

So, in the early days, companies that made transistors
hand selected the transistors coming off the line, and
binned them into different ranges for hfe, ft, or
leakage... all depending on what customers might want.

We used to see transistors of a given type with different
color paint dots on them, and later we saw "families"
of JEDEC numbered transistors, like 2N3903/2N3904, or,
2N3905/2N3906...

And, because they were expensive, designers tried their
level best to use as few transistors as they could get
away with in a given design... especially in consumer
equipment. So, they would often use the transistors a lot
closer to their hfe than one might wish, and use the
transistors that selected less good in less important
stages.

Companies like 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.

When all was said and done, and the best, the OK, and the
good enough transistors were all selected out and sold
into industry, there was PolyPaks and RadioShack.

So yes, it is common to use a part with an hfe range of
say 50 to 150 in a stage with feedback set to a gain of 10,
but it used to be quite common to use such a transistor
really close to the wall, with a gain of 100, and expect
to do some swapping when it didn't quite work out.

When you see a transistor, in a common emitter stage,
without an emitter resistor to ground, you can be pretty sure
that it is running full tilt... with as much hfe as it can
give.

-Chuck Harris

Dennis Tillman W7pF wrote:

Hi Jeff,
Transistors do not have a "specific" hFE. Look at the datasheets for the 2N3565 and the 2N2907 transistors. For that matter, you can look at the datasheet for ANY transistors. The datasheets always show a Min(imum), Nom(inal), and Max(imum), or at least two of these three values, for the transistor's hFE.

If you look a little closer at a transistor datasheet you will notice that those Min / Non / Max values are specified at a SPECIFIC collector current. The reason manufacturers specify the collector current they measured the hFE at is because the hFE can vary widely as the collector current is changed. They may also specify the temperature because hFE varies as the temperature of the transistor changes. Unless otherwise noted the temperature is usually room temperature (25C).

Circuit Design Engineers know all of this so they never design a circuit using the manufacturer's maximum hFE figures because there is always the chance they will turn out to be 1/5th of that value under actual operating conditions. Instead they use many different forms of feedback to insure the circuit is not dependent on a transistor's hFE, but on other more stable circuit components.

When you see an hFE over 100 in most cases it no longer matters whether it is 200, or 400, or 600. An hFE over 100 is excellent and no designer would design this circuit assuming all the transistors would have an hFE of at 400. The ONLY EXCEPTION is when transistors have to be hand selected to meet some specific criteria that a circuit requires.

The Fairchild 2N3565 datasheet specifies hFE as 120 min to 600 max. I will bet the circuit they are in will work just fine with any transistor with an hFE over 50.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jeff Dutky
Sent: Thursday, February 18, 2021 7:57 AM
To: TekScopes@groups.io
Subject: [TekScopes] Failed Transistor with Low h(FE)?

I'm trying to fix a DM501 that I damaged by plugging it into a faulty backplane. One of the display digits is stuck on and I think that I've narrowed the cause down to one of two transistors that drives the display chip select lines (Q348 or Q350). I removed both transistors, but when I checked them in my component tester neither one looks "blown". Q348 however (a 2N3565) has a lower hFE than the replacements I have in hand.

Here are the measured hFE for the suspect and replacement parts:

old 2N3565 (Q348): hFE=287, Vf=683
old 2N2907 (Q350): hFE=227, Vf=667

new 2N3565 (two tested): hFE=(443, 343), Vf=(673, 645) new 2N2907 (one tested): hFE=288, Vf=673

I was expected to find the failed part as a short or open. Could a failed transistor simply have a decreased gain?

-- Jeff Dutky







Re: tunnel diodes retrace lines in curve tracer

Jim Ford
 

No, not grin, Brad, groan!

I never did understand the "sock it to me" chorus in Aretha Franklin's "RESPECT". I guess I'm too young (born 1965) to get it....

Jim Ford

------ Original Message ------
From: "Brad Thompson" <brad.thompsonaa1ip@gmail.com>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 2/18/2021 8:10:22 PM
Subject: Re: [TekScopes] tunnel diodes retrace lines in curve tracer

Dennis Tillman W7pF wrote on 2/18/2021 7:14 PM:

Hi Rik,

Tunnel (Esaki) diodes rely on quantum tunneling.
<snip>

Hello--

Does anyone recall "Laugh In" (a satirical TV series of the 1960s which
featured certain repetitive routines-- one called "sock it to me" in particular).

I give you the following: "It may be a tunnel diode to you, but it's an Esaki to me...Esaki to me...."

<grin>

73--

Brad AA1IP






Re: Stan Griffiths estate sale

Jim Ford
 

I for one am so glad Tek aficionados are taking the time to sort through what must be a mountain of great old Tek gear! Even if I can't get up to Oregon to help out.

God bless you guys!

Jim Ford
Laguna Hills, California

------ Original Message ------
From: "Ryan Scott via groups.io" <tweeker42000=yahoo.com@groups.io>
To: "tekscopes@groups.io" <tekscopes@groups.io>; "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 2/18/2021 6:18:57 PM
Subject: Re: [TekScopes] Stan Griffiths estate sale

Greetings all,
Thanks for the kind Comments Dennis.
Tom Kelly and myself went over to Stan's last night and were with about 7 other people who were there.
I think Valerie and Paul want to keep it small due to Covid. Plus, I get the feeling they are a bit overwhelmed, which is understandable given Stan's impressive shop and collection. But I'm glad they are doing something. Valerie mentioned it was the right thing to do for her Dad.
Stan's shop is pretty much the same as it was the last time myself and a few others were at the weekend sales (Jan 2020) run by a family friend (Bryce I think).
Several of the 500 series scopes are still there, as well as plug ins. Note, assume that tubes were pulled from all items remaining as that is what we found with what we took home. The tube thieves struck early unfortunately. Lot's of parts / pieces, etc.
Valerie is very reasonable on the prices of the stuff remaining. I think I filled my pickup for my initial offer to Valerie of $400 and she said she was thinking $250, so we settled on $350. Tom's experience was similar.
Ultimately, I get the feeling that she wants to have her Dad's stuff end up in the hands of people like us to keep the love of Tek going.
The next sale is Saturday, but I am not sure of the time. Valerie is insistent that it does not become a 'super spreader event' so is keeping it small.
All sales appointments are being handled by Valerie's friend, Paul, who is also a good guy. But he's surprised and overwhelmed at the response thus far.
Interested parties can reach Paul via Next door, or Facebook, as per his initial ad. (Not the ideal form of communication, but he does respond)
As far as the deadline of end of next week, it appears that Valerie may have received an extension.
Tom, Tim Pierce, and Myself all agreed we will do whatever we can to save the stuff from the scrappers. We are just waiting to hear from Valerie, and we did let her know we would surely help when the time came.
I'll post more probably after this weekend.
Thanks and Regards,Ryan Scott
On Thursday, February 18, 2021, 11:47:21 AM PST, n4buq <n4buq@knology.net> wrote:

Okay, Walter, thanks for that info. I think I looked up what I could find on those model numbers back then and I don't remember whether I found that was an indication or not. Good to know.

This is for a Hameg scope which apparently uses the same CRT. I'll contact you off-list for more details.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "walter shawlee" <walter2@sphere.bc.ca>
To: TekScopes@groups.io
Sent: Thursday, February 18, 2021 1:17:59 PM
Subject: Re: [TekScopes] Stan Griffiths estate sale

Barry, the /123 means it has a graticule in the CRT part number. These are
all for Philips scopes.

regards,
walter.














Re: tunnel diodes retrace lines in curve tracer

Brad Thompson
 

Dennis Tillman W7pF wrote on 2/18/2021 7:14 PM:

Hi Rik,

Tunnel (Esaki) diodes rely on quantum tunneling.
<snip>

Hello--

Does anyone recall "Laugh In" (a satirical TV series of the 1960s which
featured certain repetitive routines-- one called "sock it to me" in particular).

I give you the following: "It may be a tunnel diode to you, but it's an Esaki to me...Esaki to me...."

<grin>

73--

Brad  AA1IP


Re: Shipped They Are

-
 

Mine haven't arrived yet and I'm starting to feel left out!

Dash -

On Thu, Feb 18, 2021 at 8:37 PM Mac Perkins <macp@whidbey.com> wrote:

My boards arrived yesterday. They look great. Many thanks to Jared for
the design and layout and to Larry for making the group buy happen and
distributing all the sets. Started assembling only to find one of the
switches was backordered. On to metalwork for the front panel.

-Mac






Re: Stan Griffiths estate sale

Ryan Scott
 

Greetings all,
Thanks for the kind Comments Dennis.
Tom Kelly and myself went over to Stan's last night and were with about 7 other people who were there.  
I think Valerie and Paul want to keep it small due to Covid.  Plus, I get the feeling they are a bit overwhelmed, which is understandable given Stan's impressive shop and collection.  But I'm glad they are doing something.  Valerie mentioned it was the right thing to do for her Dad.
Stan's shop is pretty much the same as it was the last time myself and a few others were at the weekend sales (Jan 2020) run by a family friend (Bryce I think).  
Several of the 500 series scopes are still there, as well as plug ins.  Note, assume that tubes were pulled from all items remaining as that is what we found with what we took home.  The tube thieves struck early unfortunately.   Lot's of parts / pieces, etc.  
Valerie is very reasonable on the prices of the stuff remaining.  I think I filled my pickup for my initial offer to Valerie of $400 and she said she was thinking $250, so we settled on $350.  Tom's experience was similar.
Ultimately, I get the feeling that she wants to have her Dad's stuff end up in the hands of people like us to keep the love of Tek going.  
The next sale is Saturday, but I am not sure of the time.  Valerie is insistent that it does not become a 'super spreader event' so is keeping it small.  
All sales appointments are being handled by Valerie's friend, Paul, who is also a good guy.  But he's surprised and overwhelmed at the response thus far.
Interested parties can reach Paul via Next door, or Facebook, as per his initial ad.  (Not the ideal form of communication, but he does respond)
As far as the deadline of end of next week, it appears that Valerie may have received an extension.  
Tom, Tim Pierce, and Myself all agreed we will do whatever we can to save the stuff from the scrappers.  We are just waiting to hear from Valerie, and we did let her know we would surely help when the time came.  
I'll post more probably after this weekend.  
Thanks and Regards,Ryan Scott

On Thursday, February 18, 2021, 11:47:21 AM PST, n4buq <n4buq@knology.net> wrote:

Okay, Walter, thanks for that info.  I think I looked up what I could find on those model numbers back then and I don't remember whether I found that was an indication or not.  Good to know.

This is for a Hameg scope which apparently uses the same CRT.  I'll contact you off-list for more details.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "walter shawlee" <walter2@sphere.bc.ca>
To: TekScopes@groups.io
Sent: Thursday, February 18, 2021 1:17:59 PM
Subject: Re: [TekScopes] Stan Griffiths estate sale

Barry, the /123 means it has a graticule in the CRT part number. These are
all for Philips scopes.

regards,
walter.






Re: Semtech HV multipliers + more....

n4buq
 

Hi Walter,

Did you receive my direct email today regarding the CRT from the Stuff page?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "walter shawlee" <walter2@sphere.bc.ca>
To: TekScopes@groups.io
Sent: Thursday, February 18, 2021 6:58:47 PM
Subject: [TekScopes] Semtech HV multipliers + more....

I noticed we had a bunch of these new military HV multiplier assemblies, They
may prove useful for fixing
one that has tanked in your scope. the part number is SCMA 10139, and they
are at the end of this stuff section:
https://www.sphere.bc.ca/test/stuffday.html#power2

Sorry, I don't have any specs, and my goog-fu was not able to turn anything
up even with the federal stock number.
Maybe Dennis can do a better job. Judging by the size, it would have thought
at least 4-5X.
Hopefully they may be useful to somebody.

I am starting to fill up the Tektronix portion of the page, and there's some
very sexy items in there today. My thanks to my son for the incredible
number of hours he has spent photographing all the items. Now you can really
see what everything looks like.

all the best,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.






Re: Shipped They Are

Mac Perkins
 

My boards arrived yesterday. They look great. Many thanks to Jared for the design and layout and to Larry for making the group buy happen and distributing all the sets. Started assembling only to find one of the switches was backordered. On to metalwork for the front panel.

-Mac


Re: Semtech HV multipliers + more....

-
 

Walter,

I can tell you that it's made by General Electric.

On Thu, Feb 18, 2021 at 7:59 PM walter shawlee <walter2@sphere.bc.ca> wrote:

I noticed we had a bunch of these new military HV multiplier assemblies,
They may prove useful for fixing
one that has tanked in your scope. the part number is SCMA 10139, and they
are at the end of this stuff section:
https://www.sphere.bc.ca/test/stuffday.html#power2

Sorry, I don't have any specs, and my goog-fu was not able to turn
anything up even with the federal stock number.
Maybe Dennis can do a better job. Judging by the size, it would have
thought at least 4-5X.
Hopefully they may be useful to somebody.

I am starting to fill up the Tektronix portion of the page, and there's
some very sexy items in there today. My thanks to my son for the incredible
number of hours he has spent photographing all the items. Now you can
really see what everything looks like.

all the best,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.






Semtech HV multipliers + more....

 

I noticed we had a bunch of these new military HV multiplier assemblies, They may prove useful for fixing
one that has tanked in your scope. the part number is SCMA 10139, and they are at the end of this stuff section: https://www.sphere.bc.ca/test/stuffday.html#power2

Sorry, I don't have any specs, and my goog-fu was not able to turn anything up even with the federal stock number.
Maybe Dennis can do a better job. Judging by the size, it would have thought at least 4-5X.
Hopefully they may be useful to somebody.

I am starting to fill up the Tektronix portion of the page, and there's some very sexy items in there today. My thanks to my son for the incredible number of hours he has spent photographing all the items. Now you can really see what everything looks like.

all the best,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.


Re: Cleaning Scratchy Bourns MOD pots

Renée
 

Check at the hobby shops especially train and plane builders....I have obtained brass ones
Renée

On 2/18/21 4:06 PM, - wrote:
Dennis,

Skycraft surplus store in Orlando has 2-56 and smaller screws. They
even have 0-80 screws in there. IIRC the price was about 10c each.

On Thu, Feb 18, 2021 at 7:01 PM Dennis Tillman W7pF <dennis@ridesoft.com>
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.

Thank you Ed!!!

Dennis

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Ed
Breya via groups.io
Sent: Monday, February 15, 2021 8:06 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Cleaning Scratchy Bourns MOD pots

A safer approach may be the more drastic measure of drilling out the
rivets, then you can take it apart for full access. You can replace the
rivets with long screws, about 2-56 here, or metric equivalent. I think
these and the Allen-Bradley mod-pots (that are screwed together) have been
discussed recently too. I just restored a single section A-B one recently -
a bad level control on a Wavetek 3000, that was totally intermittent. I
figured I could do it without unhooking from the wires, just long enough to
get the pot accessible. I managed to get it apart and hit it with D100,
right from the back of the rotor, which is the closest access to the
resistance element. It went back together OK, but took quite a few
rotations before it cleaned up and smoothed out. If you try to just spray
cleaners from the outside or shaft bushing, it's a long trip to expect
anything to soak in and reach the wiper and element. So, drilling a
strategically located access hole, or disassembly are the "simple" ways to
go. I think I've mentioned vacuum methods here too, recently, where you put
suction on the pot and use that in various ways to pull lots of cleaner
inside.

Ed







--
Dennis Tillman W7pF
TekScopes Moderator







Re: tunnel diodes retrace lines in curve tracer

 

Hi Rik,

Tunnel (Esaki) diodes rely on quantum tunneling. That is probably beyond the expertise of most electronics engineers to model in the way I think you mean. On the other hand it is not that hard to come up with a polynomial equation that models the shape of the I/V curve of the tunnel diode. I have done this myself. Excel can even automatically calculate a halfway decent polynomial from a spreadsheet you fill with about 20 or 30 I versus V points you plot off of a curve tracer. A really good curve fit requires about 12 or 13 polynomial terms.

The answer to your 2nd question has a lot to do with biasing. With only two leads you are stuck with very simple biasing schemes and options. That severely limits what you can do with a Tunnel Diode and achieve CONSISTENT results. Without consistency it is hard to make reliable products.
When they were first developed their simplicity and their speed were seen as big plusses. When it turned out that simplicity and consistency were not compatible that left their speed as their most interesting features. Gradually over time the semiconductor industry has learned how to make faster and faster semiconductors and that makes TDs less valuable as a circuit component.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of garp66
Sent: Thursday, February 18, 2021 10:59 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] tunnel diodes retrace lines in curve tracer


OT: Fig. 1 of the Tektronix Jack Rogers doc....

Tunnel Diodes and the stock market ??
{ apologies ... really }

I was looking at Fig. 1 in the Jack Rogers doc that Dennis graciously posted,

.. and was immediately struck, ...had just been doing an introductory "Stock Market 101 tutorial" for dummies, the other day,
simply because I know nothing about the market.

The first graph discussed in that SM 101 tutorial was called a "cup and handle" which sort-of looks like the TD Fig.1, in the Rogers Tek doc,
- but the SM graph is reversed along the horizontal axis, compared to the TD graph.

Which brings me to a question that must be obvious, and studied:
-- Have TD's been modelled mathematically in efforts to better understand TD's non-linear behaviour and to produce better units ?
Presumably there are (many ?) EE theses in this area.
and
-- Why have TD's become less of a produced and explored area of semiconductors ?
Is there something that better replaces them now ?

Rik







--
Dennis Tillman W7pF
TekScopes Moderator


Re: Cleaning Scratchy Bourns MOD pots

-
 

Dennis,

Skycraft surplus store in Orlando has 2-56 and smaller screws. They
even have 0-80 screws in there. IIRC the price was about 10c each.

On Thu, Feb 18, 2021 at 7:01 PM Dennis Tillman W7pF <dennis@ridesoft.com>
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.

Thank you Ed!!!

Dennis

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Ed
Breya via groups.io
Sent: Monday, February 15, 2021 8:06 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Cleaning Scratchy Bourns MOD pots

A safer approach may be the more drastic measure of drilling out the
rivets, then you can take it apart for full access. You can replace the
rivets with long screws, about 2-56 here, or metric equivalent. I think
these and the Allen-Bradley mod-pots (that are screwed together) have been
discussed recently too. I just restored a single section A-B one recently -
a bad level control on a Wavetek 3000, that was totally intermittent. I
figured I could do it without unhooking from the wires, just long enough to
get the pot accessible. I managed to get it apart and hit it with D100,
right from the back of the rotor, which is the closest access to the
resistance element. It went back together OK, but took quite a few
rotations before it cleaned up and smoothed out. If you try to just spray
cleaners from the outside or shaft bushing, it's a long trip to expect
anything to soak in and reach the wiper and element. So, drilling a
strategically located access hole, or disassembly are the "simple" ways to
go. I think I've mentioned vacuum methods here too, recently, where you put
suction on the pot and use that in various ways to pull lots of cleaner
inside.

Ed







--
Dennis Tillman W7pF
TekScopes Moderator






Re: Cleaning Scratchy Bourns MOD pots

 

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.

Thank you Ed!!!

Dennis

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Ed Breya via groups.io
Sent: Monday, February 15, 2021 8:06 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Cleaning Scratchy Bourns MOD pots

A safer approach may be the more drastic measure of drilling out the rivets, then you can take it apart for full access. You can replace the rivets with long screws, about 2-56 here, or metric equivalent. I think these and the Allen-Bradley mod-pots (that are screwed together) have been discussed recently too. I just restored a single section A-B one recently - a bad level control on a Wavetek 3000, that was totally intermittent. I figured I could do it without unhooking from the wires, just long enough to get the pot accessible. I managed to get it apart and hit it with D100, right from the back of the rotor, which is the closest access to the resistance element. It went back together OK, but took quite a few rotations before it cleaned up and smoothed out. If you try to just spray cleaners from the outside or shaft bushing, it's a long trip to expect anything to soak in and reach the wiper and element. So, drilling a strategically located access hole, or disassembly are the "simple" ways to go. I think I've mentioned vacuum methods here too, recently, where you put suction on the pot and use that in various ways to pull lots of cleaner inside.

Ed







--
Dennis Tillman W7pF
TekScopes Moderator


Re: tunnel diodes retrace lines in curve tracer

 

Hi Brad,
RCA made them. They came in a 1" wide stud mounted case. The stud's threads were 3/8" - 24.
The RCA 40079 had an Ip of 180 to 220 AMPS!
The RCA 40070 was rated at 90 to 110 AMPS Ip.
Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Brad Thompson
Sent: Thursday, February 18, 2021 2:22 PM

I dimly recall a mention of 100-ampere tunnel diodes, likely lab curiosities that never saw production in any meaningful quantities. One possible application might have served as switches in a DC-to-DC convertor fed by power from low-voltage sources (thermopiles?).

73--

Brad AA1IP







--
Dennis Tillman W7pF
TekScopes Moderator


Re: Failed Transistor with Low h(FE)?

 

Hi Jeff,
Transistors do not have a "specific" hFE. Look at the datasheets for the 2N3565 and the 2N2907 transistors. For that matter, you can look at the datasheet for ANY transistors. The datasheets always show a Min(imum), Nom(inal), and Max(imum), or at least two of these three values, for the transistor's hFE.

If you look a little closer at a transistor datasheet you will notice that those Min / Non / Max values are specified at a SPECIFIC collector current. The reason manufacturers specify the collector current they measured the hFE at is because the hFE can vary widely as the collector current is changed. They may also specify the temperature because hFE varies as the temperature of the transistor changes. Unless otherwise noted the temperature is usually room temperature (25C).

Circuit Design Engineers know all of this so they never design a circuit using the manufacturer's maximum hFE figures because there is always the chance they will turn out to be 1/5th of that value under actual operating conditions. Instead they use many different forms of feedback to insure the circuit is not dependent on a transistor's hFE, but on other more stable circuit components.

When you see an hFE over 100 in most cases it no longer matters whether it is 200, or 400, or 600. An hFE over 100 is excellent and no designer would design this circuit assuming all the transistors would have an hFE of at 400. The ONLY EXCEPTION is when transistors have to be hand selected to meet some specific criteria that a circuit requires.

The Fairchild 2N3565 datasheet specifies hFE as 120 min to 600 max. I will bet the circuit they are in will work just fine with any transistor with an hFE over 50.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jeff Dutky
Sent: Thursday, February 18, 2021 7:57 AM
To: TekScopes@groups.io
Subject: [TekScopes] Failed Transistor with Low h(FE)?

I'm trying to fix a DM501 that I damaged by plugging it into a faulty backplane. One of the display digits is stuck on and I think that I've narrowed the cause down to one of two transistors that drives the display chip select lines (Q348 or Q350). I removed both transistors, but when I checked them in my component tester neither one looks "blown". Q348 however (a 2N3565) has a lower hFE than the replacements I have in hand.

Here are the measured hFE for the suspect and replacement parts:

old 2N3565 (Q348): hFE=287, Vf=683
old 2N2907 (Q350): hFE=227, Vf=667

new 2N3565 (two tested): hFE=(443, 343), Vf=(673, 645) new 2N2907 (one tested): hFE=288, Vf=673

I was expected to find the failed part as a short or open. Could a failed transistor simply have a decreased gain?

-- Jeff Dutky







--
Dennis Tillman W7pF
TekScopes Moderator

4961 - 4980 of 183669