Date   

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


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

Albert Otten
 

On Thu, Jan 2, 2020 at 10:06 AM, Ed Breya wrote:


On Wed, Jan 1, 2020 at 11:43 PM, Dennis Tillman W7PF wrote:

The practical side of me says it is a very bad idea to short out a turn on a
transformer
Dennis, you should skip your planned experiment just by considering that we're
not talking about shorting out adjacent turns on a variac - the wiper is a
(carbon and copper, typically) brush, not a metal contact, which are way
different from each other. So picture not shorting with a wire, but with a
resistance network that bridges the turns, and part of the network goes to the
output terminal.

Ed


Re: Difference between Tek 494 and 494A Spectrum Analysers

Roy Thistle
 

On Tue, Dec 31, 2019 at 08:06 PM, Gary Robert Bosworth wrote:


the differences between the Tek 494 and 494A
The 494A is supposed to be an upgrade to the 494. As far as I've investigated, the frequency, time and amplitude specifications are reasonably similar... however the digital, and software/firmware, improvements to the 494A standout more.
For an example of a difference, the (frequency span)/div for the 494A is 10 Hz to 10 GHz, whilst the 494 doesn't go below 50 Hz
For another example, of another difference, the frequency stability of the timebase appears to be an order of magnitude better for the 494A
Probably if you get the two operator guides... which are similarly laid out, you can parse out, other (minor?) differences in the hardware specifications tables.
For an example of a difference that affects the way a 494A can be used over a 494... the 494A has markers, and the 494 doesn't.
There are other things along these lines too... "features and benefits"... added to the 494A's software/firmware, such as the 494A's modes, that help the 494A make complicated measurements by partly automating them, and allowing them to be made by pushing a button. The 494 doesn't have much of that.
For example, using the 494A's "Pulse Mode", you can mark the peak of a main lobe, and the peaks of the side lobes, of a signal, by just pushing a button.
There are others on this list that will know far better than me about any significant differences between the two SAs. (I haven't mentioned anything about reparability, reliability, or usability... in comparison between the two.) But, you will probably have to tell use what you are trying to do, or measure, so they can zero in on significant differences.
Very generally, I'd venture to say, Tektronix made at least marginal improvements in the hardware, and significant improvements in the software/firmware, of the 494A over the 494. And if I was thinking of getting a 494A, over a 494, I might spend a hundred or two hundred dollars more to get the 494A, for features I reckon I might need; but in reality, would probably never use.
All the best and best wishes.
Roy


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

Ed Breya
 

On Wed, Jan 1, 2020 at 11:43 PM, Dennis Tillman W7PF wrote:

The practical side of me says it is a very bad idea to short out a turn on a
transformer
Dennis, you should skip your planned experiment just by considering that we're not talking about shorting out adjacent turns on a variac - the wiper is a (carbon and copper, typically) brush, not a metal contact, which are way different from each other. So picture not shorting with a wire, but with a resistance network that bridges the turns, and part of the network goes to the output terminal.

Ed


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

Ke-Fong Lin
 

Hi everyone,

Thanks for your tips.
The repair document is exactly what I'm looking for.
I'll keep you posted.
Again thank you.

Best regards,


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

Ed Breya
 

Chuck called it right - the semi-conductive brush provides interpolation of the output between the discrete steps of the windings. It has to bridge at least two turns at any position, to give a relatively smooth transition between steps. If it didn't, the output would necessarily be discrete steps of voltage, and include "off" (disconnected) states in between, which wouldn't be good. It's a compromise to provide more or less continuous output control, and it does waste some power to heat the brush, and it contributes to wear, besides the mechanical friction. Larger variacs have extra features for better cooling of the brushgear.

The conductivity, abrasiveness, contact force, and shape of the brush have to be just right for best trade-offs between smoothness, power rating, and life. Variacs can be very tricky, but this was all pretty much perfected before any of us were born. Be happy that they work so well at their purpose.

The same sorts of issues arise in other devices where discreteness needs to be handled with smoothness and continuity, like a wirewound pot or rheostat, or the commutator of a motor.

A related, interesting insight can be gained by studying the carbon-pile, a very old-school device.

Ed


Re: 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

george edmonds
 

Hi all

I have been following this topic for some time, why not do the simple thing and measure with a DMM the voltage between cold end of the Variac and the slider when fully counter clockwise, or am I missing a point. My UK made Variac has a zero volt pad for the brush and termination of the winding.

73 George G6HIG On Thursday, 2 January 2020, 06:14:15 GMT, Chuck Harris <cfharris@...> wrote:

On the contrary, the brush is intended to connect to multiple
windings at the same time.  To prevent the problem of shorted
turns, the brush is highly resistive

You can think of the brush as a network of multiple resistors
each connecting to a different turn, and combined to form the
output.

Because each adjacent turn is less than a volt, or so, different
than the next, no great amount of heating occurs in the brush.

Yet another reason why a variac may not reach exactly zero
volts.

-Chuck Harris

Dennis Tillman W7PF wrote:
...

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.

Dennis Tillman W7PF


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

Chuck Harris
 

On the contrary, the brush is intended to connect to multiple
windings at the same time. To prevent the problem of shorted
turns, the brush is highly resistive

You can think of the brush as a network of multiple resistors
each connecting to a different turn, and combined to form the
output.

Because each adjacent turn is less than a volt, or so, different
than the next, no great amount of heating occurs in the brush.

Yet another reason why a variac may not reach exactly zero
volts.

-Chuck Harris

Dennis Tillman W7PF wrote:
...

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.

Dennis Tillman W7PF


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

Bruce Griffiths
 

Matched loads aren't usually used at mains frequencies.

Bruce

On 02 January 2020 at 18:34 KB6NAX <gumbear@...> wrote:


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




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

KB6NAX
 

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


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

 

Hi DW,
I just remembered another detail that may influence the results of what appears when the Variac is turned to "zero". Variac's are a very interesting design for a transformer for two reasons: The enamel insulation is deliberately removed from the same spot on each turn of its primary. This is done intentionally so the rotating wiper brush can make contact with that turn. Depending on where on the winding the enamel is removed the voltage may not be 0 exactly.

For my example assume there are 120 turns on the primary and the input voltage is 120VAC. Where the low side of the mains (0VAC) is connected to the very beginning of the first turn, the voltage will be 0.0VAC. At the end of the last turn where the high side of the mains is connected the voltage will be 120V. But I checked one Variac I have that I can see into and the enamel insulation is removed from each winding at about the half way point in the turn. The brush would already read 0.5VAC at this point. I don't think there is a point where the voltage is exactly 0.0VAC.

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.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of DW
Sent: Wednesday, January 01, 2020 6:36 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577D1 itching issue - Haven't touched since, currently in storage

Dennis, good response

Where I live, the mains are 120 and 240 volts. I been shocked by 120 before, it hurts. I also been shocked once by 240 which I found REALLY hurts! I have gained respect for mains voltages though it might not seem like that appears to be the case here. The idea I proposed about checking the variac with jumper leads while energized is obviously asking for trouble, I am actually glad I asked this and got the answer I need.

Thanks for your feedback with 577 collector performance data for comparison. I can see you used the magnification on the horizontal scale but regardless from my observation excellent results from your 577. My results according to my notes indicate at 25V 50mV/division a line appears 7 divisions long, with your response we see a nice comparison happening here.

I should probably explain why I am really posting about this again. My idea was to take everything from the previous post and consolidate the information so it can be easily viewed and someone might have a interesting idea or solution as they can easily and quickly look it over. I got good useful responses as a result but I fear it is at the expense of repeating myself and not letting it be.

Dennis, you make a good point of using the instrument instead of nitpicking of the details. Changing my state of mind I realize the instrument is mostly functional and I should be happy about that. I seem to have put myself in a corner worrying about details instead of enjoying the possibilities and the usefulness I could be enjoying. I will take up on that offer. If I come across something I will be sure to report back here.





--
Dennis Tillman W7PF
TekScopes Moderator


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

DW
 

Dennis, good response

Where I live, the mains are 120 and 240 volts. I been shocked by 120 before, it hurts. I also been shocked once by 240 which I found REALLY hurts! I have gained respect for mains voltages though it might not seem like that appears to be the case here. The idea I proposed about checking the variac with jumper leads while energized is obviously asking for trouble, I am actually glad I asked this and got the answer I need.

Thanks for your feedback with 577 collector performance data for comparison. I can see you used the magnification on the horizontal scale but regardless from my observation excellent results from your 577. My results according to my notes indicate at 25V 50mV/division a line appears 7 divisions long, with your response we see a nice comparison happening here.

I should probably explain why I am really posting about this again. My idea was to take everything from the previous post and consolidate the information so it can be easily viewed and someone might have a interesting idea or solution as they can easily and quickly look it over. I got good useful responses as a result but I fear it is at the expense of repeating myself and not letting it be.

Dennis, you make a good point of using the instrument instead of nitpicking of the details. Changing my state of mind I realize the instrument is mostly functional and I should be happy about that. I seem to have put myself in a corner worrying about details instead of enjoying the possibilities and the usefulness I could be enjoying. I will take up on that offer. If I come across something I will be sure to report back here.


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

Mlynch001
 

Ke-Fong Lin

Those BJT/FET switches are the same type in almost all TEKTRONIX equipment of the era. They are very prone to get dirty or gum up inside. What I do with mine is give it a shot of contact cleaner, work the switch several times let it dry and then follow with a shot of DEOXIT Spray, and finally work it several times. After about 10 -15 cycles they will free up and begin to latch. You can repeat as needed until the switch works. A very common problem as I just fixed a 465 that had a beam finder that was stuck half way between the "normal" and "find" positions. The 576 curve tracer has many of these switches, the problem with them is they are very difficult to access on the 576. But this technique works on 99% of this type of switch. I am not familiar with the +1000 switch, but is may respond to the same treatment.

Good Luck!

--
Michael Lynch
Dardanelle, AR


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

Kurt Rosenfeld
 


Re: TDS694C nvram DS1486

George Langston
 

Happy New Year All!
I got my console port running and aside from the 50 ohm overload issue, things seems to point to nvram problems (?) Here are the errors from the debug log:

"Executing Diagnostics

-> ERRORID: 358 nv storage too small more bytes requested than available
[...]
nvLibrariansDiag ............... ***FAIL***
..error details:
ERRORID: 163 diagnostic test failure nvLibrariansDiag
Libs with crcc failures:
ExtConst
[...]
twoGHz50OhmOvldConf ............ ***FAIL***
..error details:
ERRORID: 163 diagnostic test failure twoGHz50OhmOvldConf
50 ohm Overload stuck; status = 0x0
[...]
optDiagFloppyControllerIO ......0x5fffe80 (tRootTask): libError 358, lib EXTCAL, id=358, msg=more bytes requested than available
[...]
0x5fffe80 (tRootTask): libError 358, lib EXTCAL, id=358, msg=more bytes requested than available
[...]

Smalltalk/V Sun Version 1.12

Copyright (C) 1990 Object Technology International Inc.

ERRORID: 163 diagnostic test failure extended cal librarian reset
100ps > TI value(0) > 3100ps

ERROR ... step of 33792 is smaller than 50 dls

ERROR (0x2c): digPhaseCal failed

ERRORID: 110 Calibration failed measure skew got 0 avgs, expect 16
"

Although my DS1486 is still keeping time might it's 2nd battery be low and causing nvram failures?
It looks like the floppy controller is trying to write to nvram and failing?


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

J. L. Trantham
 

Dennis,

Just catching up on this. Hope I'm not too late to contribute. Let me know if you do not receive it.

Thanks to you and all the Group Members and their great contributions.

Happy New Year to All!

Joe


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

Ke-Fong Lin
 

Hi everyone,

I'm fixing a 5CT1N curve tracer plug-in.
One of the push-push switch (BJT/FET selector) is malfunctioning. It doesn't latch to FET.
The x1000 pull switch doesn't work either.
The BJT/FET switch is a 6PDT (6 poles dual throw), part number is 260-1536-00.

Do you guys have any pointer to a website or better a youtube video explaining the mechanical theory of operation?
I don't think it's a big deal, I'll just have to disassemble the switch and put it back.
But I would prefer some explanation before.

Thank you.

Best regards,