Date   
Re: Push-push switch repair (need some theory of operation)

ROLYNN PRECHTL K7DFW
 

very correct in regards to not using WD40 for switch (and potentiometer) cleaning/lube.

=========================================================================================

From this I gather that you think that the Tektronix engineers were daft when they wrote the contents of the attached.


Rolynn
Tek Bvtn and Sunset 1966-1971

Re: Push-push switch repair (need some theory of operation)

greenboxmaven
 

WD-40 can be a superior solvent to loosen up hardened grease and petroleum based crud. However, it can only be used as a first part of the cleaning process, and then must be promptly flushed out once it has done it's work. It does indeed leave a residue that is difficult to remove. DeOxit or comparable products use oxalic acid as one of their main ingredients. It is quite effective in removing oxides and tarnish from contacts.

Bruce Gentry, KA2IVY

On 1/2/20 12:31 PM, Greg Muir via Groups.Io wrote:
Bob Krassa is very correct in regards to not using WD40 for switch (and potentiometer) cleaning/lube. When used the light volatile carrier eventually evaporates leaving a heavy sticky Cosmoline type grease film that loves to collect crud. As a demonstration spray some WD40 on a tool, don’t wipe it off and leave it for a few weeks and see what happens.


Greg


Re: Push-push switch repair (need some theory of operation)

Greg Muir
 

Bob Krassa is very correct in regards to not using WD40 for switch (and potentiometer) cleaning/lube. When used the light volatile carrier eventually evaporates leaving a heavy sticky Cosmoline type grease film that loves to collect crud. As a demonstration spray some WD40 on a tool, don’t wipe it off and leave it for a few weeks and see what happens.

One first has to flush the switch with a compatible solvent (I see that Tek recommends IPA in their switch repair document) followed by a suitable lubricant and/or deoxidant. Many lean towards the Caig DeoxIT products as have I in the past but eventually came upon a product made by MG Chemicals called “Super Contact Cleaner” that has mysteriously similar characteristics as compared to the Caig products but at a considerably lower cost for larger quantities (I am not affiliated with either manufacturer or product offering). I have never had a problem using it on any switch or pot.

In all, it is not recommended to “goop up” switches and controls with those household products that don’t list use on delicate electronic devices. I always cringe when I open a piece of previously doctored equipment where the “doctor” used a non-recommended cleaner & lube and end up either cleaning all of the controls or having to replace them.

Greg

Re: MEMBERS PLEASE READ: Our annual Group.io payment is due in 2 weeks.

Hugh Vartanian
 

Hi Dennis,

Thank you and Michael for all your moderately profuse information
transmission, modulation and noise (reduction) in your duties as moderator,
bringing moderation and great knowledge to the more-than-moderately fun and
informative tek group.io group!

Best for the new year to all,
Hugh

Re: TDS3044B repair

Tom B
 

Hello All,

I finally had time to get back to fixing the TDS3044B with no display.   The problem turned out to be a bad solder joint on a surface mount choke that supplied Vcc to the display.  The crack was so small it could barely been seen on a microscope.  So, the problem was not the display.  For those that need a display for a TDS3000B, the real part number is NEC NL6448BC20-08E.  The other thing that was helpful in troubleshooting the display was a Hirose connector part number DF9A-31P.  This gave me some more room to probe the display connections on the main board.  Now I need to find the hub bits that hold the handle on the scope.  If someone knows where to get those please let me know.

Tom Bryan

On 11/7/2019 10:00 PM, Tom B wrote:
Hi Dave,

If you look at this video https://urldefense.com/v3/__https://www.youtube.com/watch?v=Z_gvjmKHN4Y__;!b9GWhakWANQ!wEpfxjysOXjFgv3ZjJzwPT00sPf81J7-h9F-OyCNJMU1-f5Y3AG4Mbyun-yU$ it shows a part number on the back of the display as 65BLM04 and on the front of the display the tag says NL6448BC20-08.  If you search each of these part numbers on ebay, the price is very different when they are actually the same part.   The cheapest price I could find for the 65BLM05 is $158.74 (used), while the cheapest price for the NL6448BC20-08 is $88 for a new part. These appear to be exactly the same part.  Any idea if there is any difference?

Tom

On 11/7/2019 2:28 PM, David Kuhn wrote:
https://urldefense.com/v3/__https://www.youtube.com/watch?time_continue=261&v=iVU0YPIeovM__;!b9GWhakWANQ!wbXzExaWmEY10yA6ddr1j7dzMVPNV7j4iMLI9u6paEFuQ5tXhS6mqOV8S_HN$

https://urldefense.com/v3/__http://lcdparts.net/UBDetail.aspx?ProductID=3796__;!b9GWhakWANQ!wbXzExaWmEY10yA6ddr1j7dzMVPNV7j4iMLI9u6paEFuQ5tXhS6mqCtAAjYv$

Looks like a perfect solution for the NEC on the TDS3000 series and in the
NEC 65BLM05 Display (virtually the same display as the one TEK uses) in the
instruments I do a lot of work on.

Unlike the video, I would not remove the paper exposing the glue when
installing the strips.  I don't want those LED strips permanently in my
LCDs in case they fail.

Dave

On Wed, Nov 6, 2019 at 11:40 PM Harvey White <madyn@...> wrote:

Re: Push-push switch repair (need some theory of operation)

Mlynch001
 

Definitely use a "plastic safe" lubricant. Also one that has proven non-corrosive characteristics. The vast majority of these switches are simply dried out, gentle cleaning and lubrication will restore most to service.

--
Michael Lynch
Dardanelle, AR

Re: Push-push switch repair (need some theory of operation)

bobkrassa
 

This swithc looks similar to the one in the Sencore PR57 AC Powerite. The basic operation is that pushing the button has to cause the latch bar to move sideways. In these switcches that as done by pushing on a fairly steep, small ramp. Looks like the ramp is on the little star wheel. Using small steep ramps to get lateral motion requires a bit of lubrication to keep the ramp smooth and working. In the Powerite, the ramps are on tiny plastic pieces.

I suggest taking the board out but before you unsolder the switch from the board, try flooding the switch with your favorite plastic-safe combination cleaner-lubricant and gently moving the parts back and forth. As a preventive measure, when these switches start to become difficult, do not use force, instead take them out and clean and lube. Do not use WD40.

73 Bob Krassa ACØJL

Tektronix 2245a Flickering Trace

William Schuler
 

Hey guys, newbie here. First of all I want to say thanks for what a great resource this place is! Made my donation two days ago.

I have a Tektronix 2245a, which I bought about a year ago. This is my first scope, and I’m still learning how to use it. I have replaced all the power supply capacitors, and all the voltages test out OK., and the unit runs OK when I first power it on. After about 10 minutes though, I start to get ghost traces and a jumpy, flickering image. Here is a link to a video I made of the unit. https://youtu.be/j6Dqke1CIRE

It is usable for what I do, which is just viewing a signal after it’s gone through a tube amp, but I would like to track down the issue. Any suggestions on where to look?

Thanks everyone, Bill

Re: MEMBERS PLEASE READ: Our annual Group.io payment is due in 2 weeks.

Joe Laffey
 

Sent in a donation PayPal from my other email address. I don’t need credit per se. So no worry.

Thanks for all the hard work.

--
Joe Laffey

On Jan 2, 2020, at 10:24 AM, Victor via Groups.Io <vmcfer=aol.com@groups.io> wrote:


Hi Dennis,
I just read your message and sent you my contribution of USD20.00.Thank you for the great job and effort you are doing all the year.This is a fantastic group. Love it !!!Wish you a Happy New Year 2020.Victor(@vmcfer)

-----Original Message-----
From: Dennis Tillman W7PF <@Dennis_Tillman_W7pF>
To: TekScopes <TekScopes@groups.io>
Sent: Tue, Dec 31, 2019 4:42 am
Subject: [TekScopes] MEMBERS PLEASE READ: Our annual Group.io payment is due in 2 weeks.

Hello everybody,
In a few minutes it will be 2020. This is much further into the future than
I thought I'd ever see. Years ago I was sure someone would have developed a
tiny ultra-thin LED display that can be imbedded into a credit card by 2020.
It would display your current outstanding balance every time the card was
inserted in a reader. If my non-futuristic credit cards only had this
imbedded into them I would certainly not be in my present predicament. I
maxed out both cards and my wife took them away. I found this puzzling
because the cards still look the same even though they don't work anymore.
It is clear to her that she can't afford to keep me. She has made this very
clear to me often in the past 2 weeks.

Since we moved to Groups.io I have been paying the annual fee they charge to
host us. I did this for two reasons:
* It was expedient when we first joined because the demise of Yahoo seemed
imminent and this was the fastest way to get up and running on Groups.io.
* Later when I asked for suggestions on alternate ways to pay for Groups.io
I didn't see anything I liked. I thank you for all of them, they were all
fine. It seemed as if they would create extra work and, more importantly,
consume more of my time (which is in very short supply). I kept each of your
suggestions for future consideration.

In 2 weeks the total amount I will have paid will be $340. This is
significant enough that I have to do something about it, and more
importantly, I need to get back into my wife's good graces. So I am asking
for small contributions via PayPal if possible to be sent to
@Dennis_Tillman_W7pF. If you include a note along with each contribution
saying it is for Groups.io that will make it easier to track. See the
postscript at the end of my post for a no-fee way to send money with PayPal.

If PayPal doesn't work for you my address is 13808 NE 26th Place, Bellevue,
WA 98005 USA. If you have an extremely rare or unusual 7000 series plugin
that is definitely an acceptable form of payment but I must advise you I
probably already have it so contact me first.

I plan to give an accounting of the total to the group once the
contributions stop. Anything over $340 will be set aside. I will find out if
Groups.io will let me pay for the following year (or years) so we don't have
to worry if I get hit by a truck. I will press them hard to let me do this
at the old price of $110/yr.

This is the Groups.io billing summary for TekScopes:
Invoice Date Plan Payment Method
Amount Paid By
#3055 01/13/19 Premium Visa XXXX XXXX XXXX 7319 USD $110
@Dennis_Tillman_W7pF
#814 01/13/18 Premium Visa XXXX XXXX XXXX 7319 USD $110
@Dennis_Tillman_W7pF
#793 12/13/17 Premium Visa XXXX XXXX XXXX 7319 USD $10
@Dennis_Tillman_W7pF
The next payment of $110 is due 01/13/2000. NOTE: It appears the annual
price for the Premium Yearly Plan will go up the first of the year to $220.

Dennis Tillman W7PF

P.S. This is a way to send money via PayPal with minimal or no fee:
NO FEE PAYMENT METHOD FOR USA TEKSCOPES MEMBERS
* Choose "Send and Request".
* By default the Send tab will be chosen for you.
* In the "Send Money" field enter @Dennis_Tillman_W7pF.
* Next PayPal will ask you: "Sending to a Friend" or "Paying for an invoice
or service"?
* Choose "Sending to a friend".
* Enter the amount.
* Press next and choose your bank account to avoid the PayPal fee.
* Press the "Send the Money" button.
* Include your email address and TekScopes ID in the Notes section.
MINIMAL FEE PAYMENT FOR FOREIGN TEKSCOPES MEMBERS
* Chose "Send to friends and family internationally".
* Select the country you are sending to (USA).
* To keep the fee to 1% where it says "Select your delivery method" choose
"Send to a PayPal Balance".
* Under "You Send", enter whatever amount in local currency converts to the
correct US currency.
* Press next.
* The email account you will be sending to is @Dennis_Tillman_W7pF.
I can't help you after this point in PayPal because I was not outside the
USA to see what happened next.
* Include your email address and TekScopes ID in the Notes section.



--
Dennis Tillman W7PF
TekScopes Moderator





Re: 577D1 itching issue - Haven't touched since, currently in storage

Chuck Harris
 

Dennis,

It is a very bad idea to short out a turn on a transformer.

But it is a very good idea to load a turn or two on a transformer...
after all, that is the transformer's job.

Here is what your variac's brush really is:

Turn1 <--Resistor---+
Turn2 <--Resistor---+-----Brush terminal
Turn3 <--Resistor---+

The voltage between turns is around a volt on most variacs.
The resistance of the brush material is chosen so that its
the power dissipation will be 1 or 2 watts, for a typical
variac.

If it is essential that a variac go all the way to zero, there
will be a metallic landing pad for the brush to land on after
it falls off of the last turn.

Absent the landing pad, the lowest voltage will be on the
order of 1/2 turn's voltage.

The variac was originally designed to be a lamp dimmer for
theater use... it replaced the very wasteful carbon pile
rheostats originally used.

This curve tracer application is forcing an oval peg into
a round hole. It sort of fits... if you force it.

-Chuck Harris

Dennis Tillman W7PF wrote:

Chuck, Bruce, and Arden,
All my life I assumed there was little more to learn from how a Variac works. They appear to be pretty simple and a very clever. This has accounted for their incredibly useful life spanning more than 85 years.

The practical side of me says it is a very bad idea to short out a turn on a transformer with 120 (more or less) turns and 120V across it. So tomorrow I will test this by intentionally hooking a short piece of wire from one turn to its neighbor while I am holding the wire in my hand. If you are right the wire won't get hot and I will learn something new. If I am right I will get burned and never trust the three of you again. Either way you have nothing to lose. :)

I will report the results either way.

Dennis Tillman W7PF

Re: MEMBERS PLEASE READ: Our annual Group.io payment is due in 2 weeks.

Victor
 

Hi Dennis,
I just read your message and sent you my contribution of USD20.00.Thank you for the great job and effort you are doing all the year.This is a fantastic group. Love it !!!Wish you a Happy New Year 2020.Victor(@vmcfer)

-----Original Message-----
From: Dennis Tillman W7PF <@Dennis_Tillman_W7pF>
To: TekScopes <TekScopes@groups.io>
Sent: Tue, Dec 31, 2019 4:42 am
Subject: [TekScopes] MEMBERS PLEASE READ: Our annual Group.io payment is due in 2 weeks.

Hello everybody,
In a few minutes it will be 2020. This is much further into the future than
I thought I'd ever see. Years ago I was sure someone would have developed a
tiny ultra-thin LED display that can be imbedded into a credit card by 2020.
It would display your current outstanding balance every time the card was
inserted in a reader. If my non-futuristic credit cards only had this
imbedded into them I would certainly not be in my present predicament. I
maxed out both cards and my wife took them away. I found this puzzling
because the cards still look the same even though they don't work anymore.
It is clear to her that she can't afford to keep me. She has made this very
clear to me often in the past 2 weeks.

Since we moved to Groups.io I have been paying the annual fee they charge to
host us. I did this for two reasons:
* It was expedient when we first joined because the demise of Yahoo seemed
imminent and this was the fastest way to get up and running on Groups.io.
* Later when I asked for suggestions on alternate ways to pay for Groups.io
I didn't see anything I liked. I thank you for all of them, they were all
fine. It seemed as if they would create extra work and, more importantly,
consume more of my time (which is in very short supply). I kept each of your
suggestions for future consideration.

In 2 weeks the total amount I will have paid will be $340. This is
significant enough that I have to do something about it, and more
importantly, I need to get back into my wife's good graces. So I am asking
for small contributions via PayPal if possible to be sent to
@Dennis_Tillman_W7pF. If you include a note along with each contribution
saying it is for Groups.io that will make it easier to track. See the
postscript at the end of my post for a no-fee way to send money with PayPal.

If PayPal doesn't work for you my address is 13808 NE 26th Place, Bellevue,
WA 98005 USA. If you have an extremely rare or unusual 7000 series plugin
that is definitely an acceptable form of payment but I must advise you I
probably already have it so contact me first.

I plan to give an accounting of the total to the group once the
contributions stop. Anything over $340 will be set aside. I will find out if
Groups.io will let me pay for the following year (or years) so we don't have
to worry if I get hit by a truck. I will press them hard to let me do this
at the old price of $110/yr.

This is the Groups.io billing summary for TekScopes:
Invoice     Date        Plan        Payment Method
Amount    Paid By   
#3055    01/13/19    Premium    Visa XXXX XXXX XXXX 7319    USD $110
@Dennis_Tillman_W7pF
#814    01/13/18    Premium    Visa XXXX XXXX XXXX 7319    USD $110
@Dennis_Tillman_W7pF
#793    12/13/17    Premium    Visa XXXX XXXX XXXX 7319    USD $10
@Dennis_Tillman_W7pF
The next payment of $110 is due 01/13/2000. NOTE: It appears the annual
price for the Premium Yearly Plan will go up the first of the year to $220.

Dennis Tillman W7PF

P.S. This is a way to send money via PayPal with minimal or no fee:
NO FEE PAYMENT METHOD FOR USA TEKSCOPES MEMBERS
* Choose "Send and Request".
* By default the Send tab will be chosen for you.
* In the "Send Money" field enter @Dennis_Tillman_W7pF.
* Next PayPal will ask you: "Sending to a Friend" or "Paying for an invoice
or service"?
* Choose "Sending to a friend".
* Enter the amount.
* Press next and choose your bank account to avoid the PayPal fee.
* Press the "Send the Money" button.
* Include your email address and TekScopes ID in the Notes section.
MINIMAL FEE PAYMENT FOR FOREIGN TEKSCOPES MEMBERS
* Chose "Send to friends and family internationally".
* Select the country you are sending to (USA).
* To keep the fee to 1% where it says "Select your delivery method" choose
"Send to a PayPal Balance".
* Under "You Send", enter whatever amount in local currency converts to the
correct US currency.
* Press next.
* The email account you will be sending to is @Dennis_Tillman_W7pF.
I can't help you after this point in PayPal because I was not outside the
USA to see what happened next.
* Include your email address and TekScopes ID in the Notes section.



--
Dennis Tillman W7PF
TekScopes Moderator

Re: TDS3012B NVRAM

David Kuhn
 

" but what about the data stored in the chip? how did you transferred the
original NVRAM content?
I think it has the number of hours and power cycles and also SPC constants
in it, right?"

I probably didn't worry about that. The calibration tables are NOT stored
in it. So once replaced, start the scope with a RESET (B TRIG) and
re-calibrate the baseline offsets and it was good. I didn't take notice if
the the number of power cycles was preserved.

Dave

On Wed, Jan 1, 2020 at 7:12 AM amirb <@amirb> wrote:

Hi David,
but what about the data stored in the chip? how did you transferred the
original NVRAM content?
I think it has the number of hours and power cycles and also SPC constants
in it, right?

Happy New Year to all :o)

On Tue, Nov 19, 2019 at 03:53 PM, David Kuhn wrote:


Ah, I just saw your pics. You are tight too. That must be a very low
profile socket. I think maybe even more so that my lead carrier pins.
My
business depends on my original TDS3032. When this chip failed, I
ordered
another TDS3032 from Alltest Instruments in NJ (~$1500). While I waited
for it to arrive, I did replace the DRAM in my original. I was way too
stupidly nervous at the time (I had to get back up and running) to dig
the
chip out, so I bought a NOS ram. It was okay and worked good. I still
use
my original as my primary (it's my baby - lol and seems to work slightly
better than my "new" one). If I have to do it again, I will definitely
do
it the way you did!

I did learn that I have to hold the B TRIG in while booting it to
initiate
that RAM chip. The screen came up in all kinds of pretty colors without
doing that - lol. Its been good now for about a year and went through
ISO17025 certification well.

Dave

On Tue, Nov 19, 2019 at 3:40 PM Daveyk021 . <daveyk021@...> wrote:

Hello Raymond,

"That is not necessary. I've added a few pictures of the initial
test-setup in my TDS3034 (now TDS3054) to the album "Clock error on
TDS3034", before clean-up. It can be seen that there's ample space for
a
normal socket and putting a Li cell on top of the RAM"

With my TDS3032 (no bloody A, or B, or C...), I tried a zero insertion
force socket, and another lower profile version, and neither would fit
in
my scope as the I/O module would hit it. I ended up using lead carrier
pins (real old school form the 1980s there, maybe earlier). With lead
carriers, it is just slightly higher (maybe 1/8" - 3/16"), and even
then,
on my scope, the chip "just" cleaned the GPIB/VGA/RS232 module. Maybe
on
the TDS3034, the chip is in a different location?

Dave

On Tue, Nov 19, 2019 at 1:03 PM Raymond Domp Frank <@Raymond
wrote:

On Tue, Nov 19, 2019 at 05:00 PM, David Kuhn wrote:


When replacing the chip, install a VERY LOW PROFILE socket (pin
carriers)
on the PCB.
That is not necessary. I've added a few pictures of the initial
test-setup in my TDS3034 (now TDS3054) to the album "Clock error on
TDS3034", before clean-up. It can be seen that there's ample space
for a
normal socket and putting a Li cell on top of the RAM

Yesterday, I wrote:

You'll find what you're looking for in my message #157465 in thread
"Clock error on TDS3034", including link to pictures of the Dallas
Module.
Link to the photos:

https://groups.io/g/TekScopes/album?id=91131

Raymond





Re: 577D1 itching issue - Haven't touched since, currently in storage

KB6NAX
 

Thanks, Albert. That's about as definitive as it can get:

https://patentimages.storage.googleapis.com/a3/1e/8c/f0878e160074e6/US2009013.pdf

Arden

-----Original Message-----
From: Albert Otten
Sent: Thursday, January 02, 2020 2:03 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577D1 itching issue - Haven't touched since, currently in storage

To refresh memories:
https://groups.io/g/TekScopes/topic/7651993

Albert
........................

Re: 577D1 itching issue - Haven't touched since, currently in storage

KB6NAX
 

That would not be a logical test, Dennis. The jumper would have to be a resistor to simulate the resistance of the brush. But if you must jumper the turns with a wire do it through a current transformer so you can tell us what amount of current flows in the jumper. Bon chance.

Arden

-----Original Message-----
From: Dennis Tillman W7PF
Sent: Wednesday, January 01, 2020 11:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577D1 itching issue - Haven't touched since, currently in storage

Chuck, Bruce, and Arden,
All my life I assumed there was little more to learn from how a Variac works. They appear to be pretty simple and a very clever. This has accounted for their incredibly useful life spanning more than 85 years.

The practical side of me says it is a very bad idea to short out a turn on a transformer with 120 (more or less) turns and 120V across it. So tomorrow I will test this by intentionally hooking a short piece of wire from one turn to its neighbor while I am holding the wire in my hand. If you are right the wire won't get hot and I will learn something new. If I am right I will get burned and never trust the three of you again. Either way you have nothing to lose. :)

I will report the results either way.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of KB6NAX
Sent: Wednesday, January 01, 2020 9:35 PM
Subject: Re: [TekScopes] 577D1 itching issue - Haven't touched since, currently in storage

Hi Dennis,

I made my donation so you have to read this (just kidding :-).

This raises another observation about the brush. It must be narrow so
it doesn't span two turns at a time else it will be shorting out one
turn to the next turn and that will short them together. They would
heat up as would the brush which is causing the short. In my example
this would cause a short across two turns that differ by exactly 1VAC.
But each winding is capable of providing from 1 to 10 Amps under
normal load situations for the size Variacs we are likely to
encounter. With a brush causing a shorted winding it isn't hard to see
that more than10 Amps could flow. To minimize the likelihood of a
short the brush comes to a chisel point. The point is slightly
narrower than one turn of wire and it is as wide as the removed enamel
area of each turn. <
I studied this on variacs and came to a different conclusion. The maximum power transfer theorem says that the source and load impedances have to be equal for maximum power to be transferred. A shorted turn is far from a matching impedance for the "primary" side, the rest of the variac winding.
In order for a large amount of power to be coupled into a shorted turn the resistance of the wire would have to be much lower than what copper provides in order for the reflected impedance to be equal to the source impedance
Think Weller soldering gun. In addition, the brush, overlapping the pair of contact points is a resistor. Intentionally, so it throws the impedance mismatch further off. The result is a very lossy mismatched transformer action, little power is transferred. Also, the brush is large enough to dissipate its heat, most of which is caused by the output load current. The losses are so small you don't realize they are there.

Arden






--
Dennis Tillman W7PF
TekScopes Moderator

Re: 577D1 itching issue - Haven't touched since, currently in storage

k1ggi
 

Dennis,
You can confidently place your trust in three other wise men, Karplus,
Tuttle, and Ohm.
https://patentimages.storage.googleapis.com/a3/1e/8c/f0878e160074e6/US200901
3.pdf
Ed, k1ggi

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dennis
Tillman W7PF
Sent: Thursday, January 02, 2020 2:43 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577D1 itching issue - Haven't touched since,
currently in storage

Chuck, Bruce, and Arden,
All my life I assumed there was little more to learn from how a Variac
works. They appear to be pretty simple and a very clever. This has accounted
for their incredibly useful life spanning more than 85 years.

The practical side of me says it is a very bad idea to short out a turn on a
transformer with 120 (more or less) turns and 120V across it. So tomorrow I
will test this by intentionally hooking a short piece of wire from one turn
to its neighbor while I am holding the wire in my hand. If you are right the
wire won't get hot and I will learn something new. If I am right I will get
burned and never trust the three of you again. Either way you have nothing
to lose. :)

I will report the results either way.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of KB6NAX
Sent: Wednesday, January 01, 2020 9:35 PM
Subject: Re: [TekScopes] 577D1 itching issue - Haven't touched since,
currently in storage

Hi Dennis,

I made my donation so you have to read this (just kidding :-).

This raises another observation about the brush. It must be narrow so
it doesn't span two turns at a time else it will be shorting out one
turn to the next turn and that will short them together. They would
heat up as would the brush which is causing the short. In my example
this would cause a short across two turns that differ by exactly 1VAC.
But each winding is capable of providing from 1 to 10 Amps under
normal load situations for the size Variacs we are likely to
encounter. With a brush causing a shorted winding it isn't hard to see
that more than10 Amps could flow. To minimize the likelihood of a
short the brush comes to a chisel point. The point is slightly
narrower than one turn of wire and it is as wide as the removed enamel
area of each turn. <
I studied this on variacs and came to a different conclusion. The maximum
power transfer theorem says that the source and load impedances have to be
equal for maximum power to be transferred. A shorted turn is far from a
matching impedance for the "primary" side, the rest of the variac winding.
In order for a large amount of power to be coupled into a shorted turn the
resistance of the wire would have to be much lower than what copper provides
in order for the reflected impedance to be equal to the source impedance.
Think Weller soldering gun. In addition, the brush, overlapping the pair of
contact points is a resistor. Intentionally, so it throws the impedance
mismatch further off. The result is a very lossy mismatched transformer
action, little power is transferred. Also, the brush is large enough to
dissipate its heat, most of which is caused by the output load current. The
losses are so small you don't realize they are there.

Arden






--
Dennis Tillman W7PF
TekScopes Moderator

Re: MEMBERS PLEASE READ: Our annual Group.io payment is due in 2 weeks.

victor.silva
 

Hi Dennis,

I made a contribution and Paypal came back with this message.
It's probably not a problem, I've never seen this kind of message.

--Victor Silva

===================================================
Your payment is being reviewed because of regulations.
We're working fast to resolve this. In the meantime, here's some information about the situation:

We usually complete this process within 72 hours, with your cooperation.
For now, this review only involves this transaction and does not affect the use of your PayPal account.
We'll send an email soon to keep you in the loop, and will follow-up with you when it's complete or if we need more information.
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Re: MEMBERS PLEASE READ: Our annual Group.io payment is due in 2 weeks.

Jason A.
 

Hi Dennis - I just sent a contribution via PayPal as well with a note that it is for TekScopes on groups.io dues. :-)

Re: 577D1 itching issue - Haven't touched since, currently in storage

Jean-Paul
 

Hello all, fine notes on 577 and variacs! The 576 is essential for power electronics design and debugging.
This monster is robust, in 25- 30 years, I have never serviced it except to replace blown out scale illum or fiber alpha display lamps! Inside clean as can be.

1/ See the app notes from GenRad/IEC and Superior Electric for brush care and function:
e.g. https://www.ietlabs.com/pdf/Manuals/GR/GR%20V20%20Variac.pdf
The manufacturers of the Variacs and Powerstats have replacement brushes available.

2/ I swapped my 577 decades ago, results on my 576 (including 100A 176 pulser!):

Step gen ON, < 0.2 div noise and trace with variac at 0. regardless of voltage range setting 15 V - 1500 V
Step gen OFF, perfect round focused dot at 0,0 regardless of voltage range setting.

I doubt if the 576 and 577 differ much in this result. Perhaps the same small variac?

Just the ramblings of an old retired EE

Jon

Need SG5030 leveling head

Melvin Gleep
 

Hi,

I need a leveling head form my SG5030, but the current pricing on EBay is out of my budget. Does anyone have a scrapped leveling head for the SG5030 they would be willing to donate?

Many thanks!

Re: MEMBERS PLEASE READ: Our annual Group.io payment is due in 2 weeks.

Jean-Marc Imbert
 

Hi Dennis, 21.50 USD is my contribution, on the way through Paypal right now.
I delayed one day because of the email address discussion.
Best wishes to all in this group and their families.
JMI