Date   

Are all 177 test fixtures created equal

DW
 

A simple question, can any 177 test fixture fit into any 577 curve tracer regardless of its build date / serial number? Thanks


Re: Need a 376-0144-00

Michael W. Lynch
 

On Wed, Dec 2, 2020 at 02:28 PM, Eric wrote:


Does anyone have or know how to duplication a 376-0144-00 This is a mechanical
shaft coupler used in the 177 fixture. It needs to be insulated up to 1600 Vdc
from the collector supply. This is one of the last pieces I need to get a 577
up and running again. I currently do not have a 3d printer so this is not an
option for me at the moment.
Eric,

I went to my 177 (JAN/1983) Fixture Mechanical parts manual and I do not see a part listed by that number. Is that extension a part of the switch? Are you sure about that Part #? I see "384-1305-00 EXTENSION SHAFT: 0.494" x 1.2" LONG. W/SHLDR". Perhaps I am overlooking this in the list?

Do you have a dimensional drawing, 3D model, STL File, etc.? One would need to make sure that the 3D printing materials used had the Dielectric strength to insulate 1600V. I can print it if we can determine that the materials that I use have the proper insulation properties.

.
Michael Lynch
Dardanelle, AR


Re: Gauging interest in a run of reproduction knob tips

thespin@...
 

I'm only considering one single part at the moment. Injection molds are extremely expensive, and I'm a mere postdoc. I only have one lecroy scope and it's relatively modern, and this project is mostly motivated by my love for my 556 and 547. I have a few options for how to make the parts -- have a mold made, or make it myself and make the parts on a friend's press. The former is expensive, and the second is labor intensive. I want to make sure I break even on the money invested or am appropriately compensated for the labor.


Re: 2710 mpu lockup on start. Help!!

 

On Wed, Dec 2, 2020 at 08:27 PM, Raymond Domp Frank wrote:


If any TTL logic is fed by this "VDD" (usually a MOS supply voltage), it'd be
on the low side (Vccmin=4.75V).
... and not just TTL, I should have said. Things like EPROMs also have a +/- 5% voltage spec.

Raymond.


Re: 2710 mpu lockup on start. Help!!

WB6GHK
 

Just a thought Rod...

I don't know where you are located but if someone in your area has a 271x you could borrow the A10 microprocessor board from, you could try subbing it to see if that corrects or impacts your 2710's problem(s). If you do swap boards, make sure you also use your original EPROMS in the substitute board since different EPROMS may not match options in your 2710.


Re: Gauging interest in a run of reproduction knob tips

Terry Gray
 

Don't think the original knob is made from bakelite. Bakelite is a "thermosetting" material and it would not be likely that it would ever crack like plastic.  It is definitely a type of plastic (melts with heat applied). Anyway, I am very happy that Evan is considering reproducing them. Should be a lot of interest in this.
    How about also reproducing the LeCroy 9300 series (you might also consider the LeCroy LA314 and similar scopes in that LA300 series--originally designed by Iwatsu) front panel knobs >>I definitely know that these would be VERY popular. The plastic shaft on the encoders break off with the knobs and both pieces end up lost. In my experience you can often repair the encoder and I think that the encoders themselves are still available (part numbers are available in the LeCroy blog history) but the knobs seem to be unobtainable. Have never seen a source for the knobs and have looked for years. You can sometimes find a knob that will work or can be modified to work but they don't match the others.  And these older LeCroy oscilloscopes are fantastic (digital scopes over 1GHz, analog up to 470MHz) and unbelievably cheap compared to original cost (for instance the LA314H originally listed for $14,000 in the 90's)>>> I picked my first LA314H up on Ebay for $99.00 BUT it had CONSIDERABLE problems in the out-sourced power supply). Reply to me if you are interested in any or all of the problems experienced. But most of the problems can be rectified easily IF you catch them early enough. It really gets bad if you wait until disaster occurs (like my first one). These SMPS are great until they fail catastrophically.      Terry

On Wednesday, December 2, 2020, 11:27:46 AM CST, thespin@gmail.com <thespin@gmail.com> wrote:


Hey all,

I've noticed that a lot of the lever knob tips have cracked due to the combination of being made of bakelite and the internal st

resses of the leaf spring. I'd like to do a short run of replacement knobs. I've tried several different 3D printing processes and haven't been totally happy with any of them. In particular, FDM tends to have pronounced layer lines, and small enough nozzles require extremely high melt flow rates restricting the choice of materials and thus colors. I also have an SLA printer, but these resins result in parts that last a few months before cracking due to UV exposure. Thus, urethane casting and injection molding are seemingly the best options. MJF or SLS may be ok but I'm not a huge fan of the texture.

If you'd be interested, I'd appreciate a response to the following survey.

https://forms.gle/U4LUT8LiVHhDk911A

Best wishes,
Evan


Re: Resistor in series

Roy Thistle
 

On Wed, Dec 2, 2020 at 11:12 AM, Dan G wrote:


Allen-Bradley fixed resistors catalog
Finally someone (Dan) took the time to opine based on the "literature."
Everyone ought to... as they say.. slam that like icon.


Re: Resistor in series

Roy Thistle
 

On Wed, Dec 2, 2020 at 08:28 AM, Jeff Dutky wrote:


I always thought of as the second simplest element of any electronic circuit.
Resistance is a parameter, in a model of order n... and how that resistance is instantiated into the World, and what the World has to "say" about it... matters... a lot.
"fixed" carbon composition resistors (fccr) are but one way to do it... they are not used much anymore, since being replaced by newer technologies... starting decades ago. They still, however, have their appropriate uses.
That said... the flaws, failures, and appropriate uses of fccr were well known over 50 years ago. A lot of that information was coded into standards (often without explanations.) A lot of the information, that was coded, was proprietary, and is now probably lost.
fccr are a kind of thing, but not a single kind of thing, and that is a distinction that matters... that distinction according to the technology that manufactured them.
The ccfr technology I've been quoting is "hot moulded," using a thermo-setting phenolic based resin, a ceramic binder, and carbon... but the devil is in the details of the properties of the materials, and the process that any one manufacturer used.
For example: there are many allotropes of solid carbon (some now known that weren't known 50 years ago)... who knows what effect that phenomenon might of had on the manufacturability of fccr?
Resistance supplied by fccr is not futile; but, it can be complicated.


Need a 376-0144-00

Eric
 

Does anyone have or know how to duplication a 376-0144-00 This is a mechanical shaft coupler used in the 177 fixture. It needs to be insulated up to 1600 Vdc from the collector supply. This is one of the last pieces I need to get a 577 up and running again. I currently do not have a 3d printer so this is not an option for me at the moment.


Re: Peter Keller book payments PayPal won't release

Chuck Harris
 

Each of us has our own situation, and our own level of
comfort with the financial organizations we deal with.

I get that you love paypal, and think they are all unicorns
and rainbows. I don't, and I truly don't think my reasons
matter to anyone but me... certainly not this group.

All Dennis needs to do to break this log jamb is to tell
paypal he shipped the books, so we can tell paypal that
we received the books.

-Chuck Harris

Larry McDavid wrote:

It is easy to use PayPal Friends and Family transfer to send funds if you have
already linked a bank checking account to your PayPal account, or if you have a cash
balance at PayPal sufficient for the funds transfer. I could be wrong but I don't
believe there is any way to do a Friends and Family funds transfer if you try to fund
with a credit card.

Remember that PayPal must pay a fee to charge your credit card, just like a
restaurant; someone has to pay that fee and free transfer using Friends and Family
would mean PayPal will be stuck paying the credit card fee. It is unrealistic to
expect PayPal to do that.

Chuck does not explain this below because he refuses to link a bank checking account
to his PayPal account. That is surely his option (he insists he has a reason) but it
limits what he can do at PayPal.

I paid Dennis using PayPal Friends and Family funds transfer and it was funded by ACH
debit of my already-linked bank checking account. I was not asked or required to
remove any PayPal protection when I did the transaction.

Some few folks may have some unique problem, possibly related to using a credit union
account instead of a bank account, but this problem is being blown way out of
proportion.

Larry


On 12/2/2020 10:17 AM, Chuck Harris wrote:
I have written you personally, but I may as well tell the group
why there is a problem publicly.

Paypal accounts that are using a credit card to make payments
cannot do friends and family, without incurring a cash advance
charge from their CC company, and starting the interest rolling
on the balance on their card.... even if they pay the full bill
every month.

So, to sent cash using paypal, we have to use the purchase goods
and services method.  That allows for an ordinary charge on our
credit cards.

To make this work, though, he has to lie to paypal and say that
he has shipped the book.  Then we can lie to paypal and say that
we have received the book.

IT MUST BE DONE IN THIS ORDER!

If Dennis doesn't tell paypal he has shipped the book, he will
have to wait 30 days before paypal will release the funds.

If Dennis does tell paypal he has shipped the book, then we
can click on the Received button, and his funds will be released
immediately.  (Well, unless he has other problems with paypal,
like a history of not sending stuff, or a lot of returns...)

-Chuck Harris
...


Re: Peter Keller book payments PayPal won't release

Eric
 

I am not saying it was Dennis's fault nor that we should change anything that is currently going on I am suggesting generating NEW low dollar transactions to get the reputation us so that this is no longer and issue.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Vince Vielhaber
Sent: Wednesday, December 2, 2020 3:10 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Peter Keller book payments PayPal won't release

It's not Dennis' fault. Plenty of people have paid with F&F with no issues. PayPal will stop your ability to pay F&F if 1) you've abused it and/or 2) you've had bounced transactions (bought something and the bank said NSF or had some other reason to decline it.

If you accept F&F and then use PP to send something to that person, PP will change it from F&F to product purchased and take the fee.

Vince - K8ZW.

On 12/02/2020 03:03 PM, Eric wrote:
If there is an underlying issue with Dennis's pay pal reputation as this seems to be an ongoing issue and it is just a few button clicks to make badly written software happy If there is enough transactions to build the reputation this would no longer be in issue in the future. I would be more then happy to buy a string of $0.50 or $1.00 random Tek vaper ware from Dennis and just say I received the parts I am guessing about 50 ish transactions should make the pay pal software happy that Dennis is not a scammer and we would be able to proceed as normal.

Thoughts on this?

Eric
-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Chuck
Harris
Sent: Wednesday, December 2, 2020 1:18 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Peter Keller book payments PayPal won't
release

I have written you personally, but I may as well tell the group why there is a problem publicly.

Paypal accounts that are using a credit card to make payments cannot do friends and family, without incurring a cash advance charge from their CC company, and starting the interest rolling on the balance on their card.... even if they pay the full bill every month.

So, to sent cash using paypal, we have to use the purchase goods and services method. That allows for an ordinary charge on our credit cards.

To make this work, though, he has to lie to paypal and say that he has shipped the book. Then we can lie to paypal and say that we have received the book.

IT MUST BE DONE IN THIS ORDER!

If Dennis doesn't tell paypal he has shipped the book, he will have to wait 30 days before paypal will release the funds.

If Dennis does tell paypal he has shipped the book, then we can click
on the Received button, and his funds will be released immediately.
(Well, unless he has other problems with paypal, like a history of not
sending stuff, or a lot of returns...)

-Chuck Harris

Dennis Tillman W7pF wrote:
The following people have sent payment for Peter Keller's book but
PayPal is holding the funds and will not release them to me so I can
pay Peter Keller for your book(s).
BL, $35.63, ON HOLD Nov 22
SJ, $68.53, ON HOLD Nov 22
BG, $38.54, ON HOLD Nov 23
CH, $73.93, ON HOLD Nov 23
DG, $68.53, ON HOLD Nov 23
DG, $6.20, ON HOLD Nov 24
LS, $35.63, ON HOLD Nov 26

PayPal describes these transactions as "Pending". It explains that
"This payment is in your on hold balance. Update your shipping info
or order status to get your money sooner."

If each of you will give me permission to tell PayPal one of the following:
1) I shipped, or I am planning to ship, Peter Keller's book to you;
2) Your payment was for a service or virtual product which doesn't
need to ship.

Then I think PayPal will release your payment.

Dennis Tillman W7pF














--
K8ZW http://www.metalworkingfun.com http://www.hamradio.fun


Re: Peter Keller book payments PayPal won't release

Vince Vielhaber
 

It's not Dennis' fault. Plenty of people have paid with F&F with no issues. PayPal will stop your ability to pay F&F if 1) you've abused it and/or 2) you've had bounced transactions (bought something and the bank said NSF or had some other reason to decline it.

If you accept F&F and then use PP to send something to that person, PP will change it from F&F to product purchased and take the fee.

Vince - K8ZW.

On 12/02/2020 03:03 PM, Eric wrote:
If there is an underlying issue with Dennis's pay pal reputation as this seems to be an ongoing issue and it is just a few button clicks to make badly written software happy If there is enough transactions to build the reputation this would no longer be in issue in the future. I would be more then happy to buy a string of $0.50 or $1.00 random Tek vaper ware from Dennis and just say I received the parts I am guessing about 50 ish transactions should make the pay pal software happy that Dennis is not a scammer and we would be able to proceed as normal.

Thoughts on this?

Eric
-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Chuck Harris
Sent: Wednesday, December 2, 2020 1:18 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Peter Keller book payments PayPal won't release

I have written you personally, but I may as well tell the group why there is a problem publicly.

Paypal accounts that are using a credit card to make payments cannot do friends and family, without incurring a cash advance charge from their CC company, and starting the interest rolling on the balance on their card.... even if they pay the full bill every month.

So, to sent cash using paypal, we have to use the purchase goods and services method. That allows for an ordinary charge on our credit cards.

To make this work, though, he has to lie to paypal and say that he has shipped the book. Then we can lie to paypal and say that we have received the book.

IT MUST BE DONE IN THIS ORDER!

If Dennis doesn't tell paypal he has shipped the book, he will have to wait 30 days before paypal will release the funds.

If Dennis does tell paypal he has shipped the book, then we can click on the Received button, and his funds will be released immediately. (Well, unless he has other problems with paypal, like a history of not sending stuff, or a lot of returns...)

-Chuck Harris

Dennis Tillman W7pF wrote:
The following people have sent payment for Peter Keller's book but
PayPal is holding the funds and will not release them to me so I can
pay Peter Keller for your book(s).
BL, $35.63, ON HOLD Nov 22
SJ, $68.53, ON HOLD Nov 22
BG, $38.54, ON HOLD Nov 23
CH, $73.93, ON HOLD Nov 23
DG, $68.53, ON HOLD Nov 23
DG, $6.20, ON HOLD Nov 24
LS, $35.63, ON HOLD Nov 26

PayPal describes these transactions as "Pending". It explains that
"This payment is in your on hold balance. Update your shipping info or
order status to get your money sooner."

If each of you will give me permission to tell PayPal one of the following:
1) I shipped, or I am planning to ship, Peter Keller's book to you;
2) Your payment was for a service or virtual product which doesn't
need to ship.

Then I think PayPal will release your payment.

Dennis Tillman W7pF














Re: Peter Keller book payments PayPal won't release

Eric
 

If there is an underlying issue with Dennis's pay pal reputation as this seems to be an ongoing issue and it is just a few button clicks to make badly written software happy If there is enough transactions to build the reputation this would no longer be in issue in the future. I would be more then happy to buy a string of $0.50 or $1.00 random Tek vaper ware from Dennis and just say I received the parts I am guessing about 50 ish transactions should make the pay pal software happy that Dennis is not a scammer and we would be able to proceed as normal.

Thoughts on this?

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Chuck Harris
Sent: Wednesday, December 2, 2020 1:18 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Peter Keller book payments PayPal won't release

I have written you personally, but I may as well tell the group why there is a problem publicly.

Paypal accounts that are using a credit card to make payments cannot do friends and family, without incurring a cash advance charge from their CC company, and starting the interest rolling on the balance on their card.... even if they pay the full bill every month.

So, to sent cash using paypal, we have to use the purchase goods and services method. That allows for an ordinary charge on our credit cards.

To make this work, though, he has to lie to paypal and say that he has shipped the book. Then we can lie to paypal and say that we have received the book.

IT MUST BE DONE IN THIS ORDER!

If Dennis doesn't tell paypal he has shipped the book, he will have to wait 30 days before paypal will release the funds.

If Dennis does tell paypal he has shipped the book, then we can click on the Received button, and his funds will be released immediately. (Well, unless he has other problems with paypal, like a history of not sending stuff, or a lot of returns...)

-Chuck Harris

Dennis Tillman W7pF wrote:
The following people have sent payment for Peter Keller's book but
PayPal is holding the funds and will not release them to me so I can
pay Peter Keller for your book(s).
BL, $35.63, ON HOLD Nov 22
SJ, $68.53, ON HOLD Nov 22
BG, $38.54, ON HOLD Nov 23
CH, $73.93, ON HOLD Nov 23
DG, $68.53, ON HOLD Nov 23
DG, $6.20, ON HOLD Nov 24
LS, $35.63, ON HOLD Nov 26

PayPal describes these transactions as "Pending". It explains that
"This payment is in your on hold balance. Update your shipping info or
order status to get your money sooner."

If each of you will give me permission to tell PayPal one of the following:
1) I shipped, or I am planning to ship, Peter Keller's book to you;
2) Your payment was for a service or virtual product which doesn't
need to ship.

Then I think PayPal will release your payment.

Dennis Tillman W7pF






Re: Gauging interest in a run of reproduction knob tips

Dave Wise
 

Don't get me wrong, I'd love to get good reproductions. The tact-switch caps are better than bare levers, but I only put them on because cracked falling-off bats MAKE ME CRAZY.

Dave Wise
________________________________________
From: David Wise
Sent: Wednesday, December 02, 2020 10:36 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Gauging interest in a run of reproduction knob tips

The Tek lever knob tips are P/N 366-0215-xx. They're widely used, e.g. Type 453 and 547 scopes and 1A1, 1A2, 1A4, and 1A5 plugins.

For what it's worth, I replace broken ones with the cylindrical tact-switch cap made by E-Switch, part number 1RDGR, $0.18 each at Mouser.
Description is "Switch Bezels / Switch Caps RND DARK GRAY CAP". It doesn't have the feel of the original but it works and it stays in place.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of thespin via groups.io <thespin=gmail.com@groups.io>
Sent: Wednesday, December 02, 2020 9:27 AM
To: TekScopes@groups.io
Subject: [TekScopes] Gauging interest in a run of reproduction knob tips

Hey all,

I've noticed that a lot of the lever knob tips have cracked due to the combination of being made of bakelite and the internal stresses of the leaf spring. I'd like to do a short run of replacement knobs. I've tried several different 3D printing processes and haven't been totally happy with any of them. In particular, FDM tends to have pronounced layer lines, and small enough nozzles require extremely high melt flow rates restricting the choice of materials and thus colors. I also have an SLA printer, but these resins result in parts that last a few months before cracking due to UV exposure. Thus, urethane casting and injection molding are seemingly the best options. MJF or SLS may be ok but I'm not a huge fan of the texture.

If you'd be interested, I'd appreciate a response to the following survey.

https://forms.gle/U4LUT8LiVHhDk911A

Best wishes,
Evan


Re: Resistor in series

Tom Lee
 

Thanks very much for finding that source, Dan -- our emails crossed in transit. I see that the manufacturer recommended quite a longer bake time than I had used. Very interesting to know.

Also, thanks for the note about soldering temp effects on the resistors. The 1/8W 47 ohm resistors that terminate the high-Z vert. preamp in the 485 is another one to add to your list. It drifts upward and causes the low-freq and high-freq gains to differ, adding a bad doublet tail to the step response. You can tweak this out for a while, but eventually you run out of tweaking room and the resistor has to be replaced. A modern SMD resistor fits nicely in its place.

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 12/2/2020 11:12, Dan G wrote:
On Wed, Dec 2, 2020 at 01:19 PM, Jeff Dutky wrote:

If I were going to "bake" some of these to see how that affects them, how
would I go about doing this?
Hi Jeff,

An old Allen-Bradley fixed resistors catalog specifies the correct
conditioning parameters. Here is a quote of the relevant section:

Effect of moisture absorption - Moisture attraction is a
generic characteristic of carbon, and when the Hot-Molded
Carbon Composition resistor absorbs moisture, e.g., during
shipment and storage, its resistance value will always
increase. Under high humidity conditions it is not unusual
for parts to increase 6% in resistance value in as little as
72 hours. The characteristic is reversible, and dehumidifying
the parts is easily accomplished either by storing them in a
controlled, low-humidity area or by conditioning them in a
convection over at 100 C. The chart below lists the proper
conditioning parameters.

Rating Conditioning Time @ 100 C
1/8W 25 Hours
1/4W 50 Hours
1/2W 75 Hours
1W 120 Hours
2W 130 Hours
I use a temperature-controlled oven, with a temperature sensor placed near
the resistors on the rack. I set the oven controller to maintain 95 C. The
actual temperature tends to vary +/- 3 C, which keeps it within 100 C.

Also, an important aspect that has not been discussed in this thread so far
is the effect of moisture ingress on soldering. Namely, it is my understanding
that if there is any moisture trapped inside the CC resistor at the time of
soldering, the high soldering temperature will cause this moisture to
vaporize so rapidly that it can create micro-fissures in the resistor material,
and especially near the carbon comp/lead terminal interface. Any such
damage is permanent, and will then often get worse over time.

The smaller the resistor, the more vulnerable it is to this type of damage.
The small 1/8W carbon comp resistors that Tektronix used in
high bandwidth equipment in the 60s and 70s (S- series sampling heads,
7S- and 7T- plugins, DC508, etc.) are _extremely_ fragile in this regard.

I place the baked resistors in a hermetically sealed container
immediately after baking is finished, and make sure to complete all
soldering within an hour or two after that. I never attempt to solder
CC resistors that may have absorbed moisture, and always use
heat sinks during soldering.


dan




Re: 2710 mpu lockup on start. Help!!

 

On Wed, Dec 2, 2020 at 04:03 PM, <Rodric@earthlink.net> wrote:


VDD is good (4.78 V)
I don't know this instrument. If any TTL logic is fed by this "VDD" (usually a MOS supply voltage), it'd be on the low side (Vccmin=4.75V). Probably even lower further downstream.

Raymond


Re: Peter Keller book payments PayPal won't release

Larry McDavid
 

It is easy to use PayPal Friends and Family transfer to send funds if you have already linked a bank checking account to your PayPal account, or if you have a cash balance at PayPal sufficient for the funds transfer. I could be wrong but I don't believe there is any way to do a Friends and Family funds transfer if you try to fund with a credit card.

Remember that PayPal must pay a fee to charge your credit card, just like a restaurant; someone has to pay that fee and free transfer using Friends and Family would mean PayPal will be stuck paying the credit card fee. It is unrealistic to expect PayPal to do that.

Chuck does not explain this below because he refuses to link a bank checking account to his PayPal account. That is surely his option (he insists he has a reason) but it limits what he can do at PayPal.

I paid Dennis using PayPal Friends and Family funds transfer and it was funded by ACH debit of my already-linked bank checking account. I was not asked or required to remove any PayPal protection when I did the transaction.

Some few folks may have some unique problem, possibly related to using a credit union account instead of a bank account, but this problem is being blown way out of proportion.

Larry


On 12/2/2020 10:17 AM, Chuck Harris wrote:
I have written you personally, but I may as well tell the group
why there is a problem publicly.
Paypal accounts that are using a credit card to make payments
cannot do friends and family, without incurring a cash advance
charge from their CC company, and starting the interest rolling
on the balance on their card.... even if they pay the full bill
every month.
So, to sent cash using paypal, we have to use the purchase goods
and services method. That allows for an ordinary charge on our
credit cards.
To make this work, though, he has to lie to paypal and say that
he has shipped the book. Then we can lie to paypal and say that
we have received the book.
IT MUST BE DONE IN THIS ORDER!
If Dennis doesn't tell paypal he has shipped the book, he will
have to wait 30 days before paypal will release the funds.
If Dennis does tell paypal he has shipped the book, then we
can click on the Received button, and his funds will be released
immediately. (Well, unless he has other problems with paypal,
like a history of not sending stuff, or a lot of returns...)
-Chuck Harris
...

--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)


Re: Resistor in series

Tom Lee
 

I would leave those resistors in place. Their exact value is quite non-critical, as Ed explained in his excellent post. They're there just to make sure that the feedback loop stays closed. But there's nothing to stop you from replacing them -- it's your scope!

If you want to try the bake method, a recipe that I've used in the past (just to see what happens) is to heat them for about an hour at boiling temp or a bit above. That brought almost all of a handful of grossly off-spec resistors back to within tolerance (or nearly so). I would expect their low-frequency noise to have dropped as well, but I made no measurements.

--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 12/2/2020 10:19, Jeff Dutky wrote:
Okay, to bring this a little bit back to the original topic:

I received the first batch of replacement NOS carbon comp resistors today.

I checked them with a multimeter and they all read a bit high: between 7.7 kΩ and 7.9 kΩ, which is between 2.5% and 5% off. But these also appear to be marked at 10% tolerance (it's hard to tell if the metallic band is silver or gold), so that's still well within spec, and much better than the two that are in-circuit on the 475A. It's also hard to tell from the pictures I took of the circuit board ( https://groups.io/g/TekScopes/photo/257066/0?p=Created,,,20,2,0,0 ), but the upright resistors may not have any tolerance band, meaning that they are 20% tolerance, which would put them just within tolerance with their present measured values of ~9 kΩ. The service manual, however, indicates that they are supposed to be 5% tolerance parts.

I'm considering taking the lowest measured values and using them to replace the existing (drifted) parts, but it's going to be tough getting the iron in to de-solder them from the board.

If I were going to "bake" some of these to see how that affects them, how would I go about doing this?

-- Jeff Dutky




Re: Gauging interest in a run of reproduction knob tips

greenboxmaven
 

If you are speaking of the small teardrop shaped knobs for the lever switches, I think there is considerable need for them. I could use about fifteen of them right now, and more later. Most of the ones I need are to replace missing ones, but the metal spring inside several has started a crack in the knob which will only spread.

Bruce Gentry, KA2IVY

On 12/2/20 13:36, Dave Wise wrote:
The Tek lever knob tips are P/N 366-0215-xx. They're widely used, e.g. Type 453 and 547 scopes and 1A1, 1A2, 1A4, and 1A5 plugins.

For what it's worth, I replace broken ones with the cylindrical tact-switch cap made by E-Switch, part number 1RDGR, $0.18 each at Mouser.
Description is "Switch Bezels / Switch Caps RND DARK GRAY CAP". It doesn't have the feel of the original but it works and it stays in place.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of thespin via groups.io <thespin=gmail.com@groups.io>
Sent: Wednesday, December 02, 2020 9:27 AM
To: TekScopes@groups.io
Subject: [TekScopes] Gauging interest in a run of reproduction knob tips

Hey all,

I've noticed that a lot of the lever knob tips have cracked due to the combination of being made of bakelite and the internal stresses of the leaf spring. I'd like to do a short run of replacement knobs. I've tried several different 3D printing processes and haven't been totally happy with any of them. In particular, FDM tends to have pronounced layer lines, and small enough nozzles require extremely high melt flow rates restricting the choice of materials and thus colors. I also have an SLA printer, but these resins result in parts that last a few months before cracking due to UV exposure. Thus, urethane casting and injection molding are seemingly the best options. MJF or SLS may be ok but I'm not a huge fan of the texture.

If you'd be interested, I'd appreciate a response to the following survey.

https://forms.gle/U4LUT8LiVHhDk911A

Best wishes,
Evan












Re: Resistor in series

Dan G
 

On Wed, Dec 2, 2020 at 01:19 PM, Jeff Dutky wrote:

If I were going to "bake" some of these to see how that affects them, how
would I go about doing this?
Hi Jeff,

An old Allen-Bradley fixed resistors catalog specifies the correct
conditioning parameters. Here is a quote of the relevant section:

Effect of moisture absorption - Moisture attraction is a
generic characteristic of carbon, and when the Hot-Molded
Carbon Composition resistor absorbs moisture, e.g., during
shipment and storage, its resistance value will always
increase. Under high humidity conditions it is not unusual
for parts to increase 6% in resistance value in as little as
72 hours. The characteristic is reversible, and dehumidifying
the parts is easily accomplished either by storing them in a
controlled, low-humidity area or by conditioning them in a
convection over at 100 C. The chart below lists the proper
conditioning parameters.

Rating Conditioning Time @ 100 C
1/8W 25 Hours
1/4W 50 Hours
1/2W 75 Hours
1W 120 Hours
2W 130 Hours
I use a temperature-controlled oven, with a temperature sensor placed near
the resistors on the rack. I set the oven controller to maintain 95 C. The
actual temperature tends to vary +/- 3 C, which keeps it within 100 C.

Also, an important aspect that has not been discussed in this thread so far
is the effect of moisture ingress on soldering. Namely, it is my understanding
that if there is any moisture trapped inside the CC resistor at the time of
soldering, the high soldering temperature will cause this moisture to
vaporize so rapidly that it can create micro-fissures in the resistor material,
and especially near the carbon comp/lead terminal interface. Any such
damage is permanent, and will then often get worse over time.

The smaller the resistor, the more vulnerable it is to this type of damage.
The small 1/8W carbon comp resistors that Tektronix used in
high bandwidth equipment in the 60s and 70s (S- series sampling heads,
7S- and 7T- plugins, DC508, etc.) are _extremely_ fragile in this regard.

I place the baked resistors in a hermetically sealed container
immediately after baking is finished, and make sure to complete all
soldering within an hour or two after that. I never attempt to solder
CC resistors that may have absorbed moisture, and always use
heat sinks during soldering.


dan

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