Date   

Re: Wrong cable... How bad is it?

Tom Lee
 

The solution depends on what problem you're trying to solve. If you need to meet the stringent flatness spec of the SG503, then you need the cable (or equivalent). Dennis has published an excellent analysis comparing off-the-shelf cables with the official Tek cable. To meet Tek's spec, you cannot assume that "50 ohm cable" is 50 ohm cable. Most are 52 ohms, nominally, and not controlled to that value with any precision.

The need for the special cable is caused by the SG503's sensing the amplitude at the front panel connector, not at the ultimate point of delivery. As such, any load mismatch will cause some non-unity VSWR and thus, some departure from flatness. Also, cable loss won't be corrected, either, but that's a secondary problem.

If you don't need the factory-level flatness, you can get by with short lengths of regular cable. The degradation in flatness will certainly be measurable, but may be acceptable (again, depending on your use case). Note that the SG503's sensitivity to cable characteristics is shared by virtually every other sig gen on the planet.

The SG504 replaces the need for expensive coax with the need for a special levelling head (which is almost never found accompanying the plug-in -- see the many efforts to homebrew them, such as the nice one by our own David Partridge). The 504 uses a different arrangement where the amplitude  is sensed at the point of delivery, rather than at the generator's front panel connector. If you use no (or negligible) additional cable, the amplitude will be controlled to exquisite precision by the levelling/leveling loop.

-- Cheers
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 2/8/2021 14:20, G Hopper wrote:
This is an interesting thread since I, like Stephen, have long assumed my
cables were ok. I'm no longer 100% sure and need to check them.

However, what REALLY caught my attention was Jon's comment "For use over 20
MHz eg with SG503 or SG504 or fast pulses like PG506, a calibrated
special 1/2 m Tektronix cable is preffered..."

Having one of those devices, and not having the special cable, what's the
solution?

Is the solution to the issue: getting/building a cable (with 50 ohm coax)
of exactly 1/2m length? or is it something else? There must be a solution
other than acquiring an original cable since Tektronix would have had a
specification and had cables made to that spec. I've got to believe that
it's something that mere mortals can reproduce. :-)

If it is, where can one gather the information?

Cheers,
Grant

On Mon, Feb 8, 2021 at 2:09 PM Jean-Paul <jonpaul@ix.netcom.com> wrote:

Stephen welcoming to the wonderful world of wired transmission of Signals,
researched since the earliest days days of Telegraph, telephone and vidéo.

First, câble Zo is important in a matched system eg 50 ohm cal gen and 50
ohm load.
For audio tests with 1 M Ohm , no difference.

As the frequency, and bandwidth go up, and rise times get short, the Zo
is more and more critical to obtaining low reflections, as is the cables
VSWR, attenuation and phase vs legnth and frequency.

Thus RG174/u is 50 ohm, but dia ~ 3 mm so rather high atten. db/ meter,
while RG58/u, is thicker and RG6/u very thick 12 mm so much mess atten per
m thoughts all are 50 Ohm.

For use over 20 MHz eg with SG503 or SG504 or fast pulses like PG506, a
calibrated special 1/2 m Tektronix cable is preffered . Generally the
shorter the cables the better for cal use.
Finally the wire and insulation quality and connectors precision are
factors.

We use the Tektronix and Genrad precision cables for critical applications
and avoid the cheap, poorly made Chinese clones.

Suggest that you consult the Belden Wire site papers and applications
notes, as well as the detailed specifications on whatever cables,
connectors and wire you use.

Bon courage

Jon










Re: 2445B 2467B - non Tek probes

 

On Tue, Feb 9, 2021 at 12:54 AM, Ondrej Pavelka wrote:


I can clearly see the Testek probes are superior
to P6136 but the lack of the coding ring is driving me mad.
I couldn't find 600 MHz Testec (Testek?) passive probes, 500 MHz being the max. What did you find that makes the Testek probes superior to P6136's? Are you talking about the (1.2 GHz) active ones?

In most cases, it doesn't make much sense to use any passive probe at these high frequencies, because of their large input capacitance of around 10 pF min. I don't know any passive 1:10 probes spec'ed higher than 500 MHz.

Tek P6137's aren't very expensive and recommended for the 2465B/67B. I guess that makes more sense than trying to add a readout feature.

Raymond


Re: Sick SG504

Tom Lee
 

Thank you for the very helpful information, John. One thing that's always mystified me is that the Philips/NXP BFR94A doesn't even have the same die as the "original" BFR94A in the SOT122E. The breakdwon voltages, capacitances, max IC, ft, etc. are all different. I can't remember ever encountering a similar situation where the same transistor part number is used for such different devices (I'm excluding the data-compressed SMD marking codes).

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 2/8/2021 16:08, John Bennett wrote:
Eric,
I misspoke regarding the package type for Q70 (I should have looked it up). You want the 4-tab studded package (it has two emitter tabs) referred to in various data sheets as SOT122E, SOT48, and I think TO-117 (not TO-128). In any event, the BFR94A in that form factor should work. I have also used the the Motorola MRF587 and MRF511 with some success, although there are trade offs:
Typ. fT (GHz) VCEmax (V) Max Diss (W) ICmax (ma)
BRF94A 3.5 25 3.5 300
MRF587 5.5 17 5 200
MRF511 2.1 30 5 250

I generally go with the BFR94A, which are usually easy to find on eBay.
Good luck with your project!
john




Re: 549 transformer question

Chuck Harris <cfharris@...>
 

Anything you put on or in a coil like this is going to
affect the winding's capacitance, leakage, and Q.

You can use a layer wind, preferably a retrace wind on
these transformers, where you wind one layer, from left
to right, put a wrap of kapton tape, return to the left
side, cover the "retrace" with a bit of kapton tape, and
then wind the next layer... wash rinse, repeat.

It is more effort in the winding, but will ultimately do
just as good of a job. You have to use bifilar for the
first 500 or so turns, though.

No corona dope is necessary. If you use a layer of kapton
tape over every layer, on impregnation is necessary, as the
adhesive will do a good enough job.

There is no good reason to wind with anything bigger than
#38. It is already bigger than necessary.

RTV is a bad idea, unless it is a two part meant for coil
winding. It will affect the capacitance, leakage, and "Q"
of the finished coil.

I have wound hundreds of these coils with good success.

I would guess there are no more than another 100 customers
for 100 more transformers left in our community. That hardly
qualifies as plenty of business.

-Chuck Harris

Mark Vincent wrote:

Chuck or anyone else with knowledge,

I was wondering if any/some/none of the following could be used in the rewinding of the transformers that might make operation like it should be for a long life. Kapton between the layers, corona dope over layers and GE RTV or similar over the completed core. I did use the RTV under the original white RTV and around the PDA of a crt that the original white had separated from the outer envelope. It now works fine with no corona or arcing. This is the 21kv PDA type crt.

Would increasing the wire size, e.g. 38ga to 36ga, be better for winding(s)? I know the Cu loss would be lower and may be easier to work with being a larger diameter.

By the replies looking for a rewinding source, the one(s) that get a way to rewind the cores that work and hold up would be getting plenty of business. If I had a transformer rewound that the core was too large to allow the filament windings for the 5642s, I would not mind using high voltage solid state diodes. That one modification to have a working scope would be great.

Would Amidon have ferrite cores that would work? I know they make excellent quality products.

These are ideas I threw out to see if any are any good.

Mark






Re: Sick SG504

John Bennett
 

Eric,
I misspoke regarding the package type for Q70 (I should have looked it up). You want the 4-tab studded package (it has two emitter tabs) referred to in various data sheets as SOT122E, SOT48, and I think TO-117 (not TO-128). In any event, the BFR94A in that form factor should work. I have also used the the Motorola MRF587 and MRF511 with some success, although there are trade offs:
Typ. fT (GHz) VCEmax (V) Max Diss (W) ICmax (ma)
BRF94A 3.5 25 3.5 300
MRF587 5.5 17 5 200
MRF511 2.1 30 5 250

I generally go with the BFR94A, which are usually easy to find on eBay.
Good luck with your project!
john


Re: Help for DC503A universal counter repair

Attilio
 

Hi everyone,
I solved the problem by inserting a pull-up resistor on the blanking line (pin 11 of the LS7031).
One problem remains: the zero before the decimal point does not stay lit, I think it is the DPI input, pin 10 of the LS7031, but I leave it like that, just know it.

I doubt that the original Tektronix LSI LS7031 is slightly different from the standard LS7031, or it may be that the original is from 1983, while the one I found is from 1980, or finally that the new LS7031 is faulty, I don't know...

--Cheers
Attilio


2445B 2467B - non Tek probes

Ondrej Pavelka
 

Hi folks,

I have 2445B for quite many years, thanks to this awesome group and some super helpful members like Siggy or Chuck and others I dealt with leaky caps on the A5 board, backed up and copied calibration over. It's all good and I can't really be happier. Well except I just acquired 2467B in basically new condition. The only problem I have the P6136 probes becoming brittle and falling apart. The 2467B came with two Testek 600MHz probes but as much as I could live without the ID button, not having the coded ring is a nightmare when swapping between probes.
Anyone on here managed to 3D print or make in any other way adapter which would make the probe coded? I can clearly see the Testek probes are superior to P6136 but the lack of the coding ring is driving me mad. I was swapping between coded and unconditional probes during one calibration of an instrument and guess what..... Yes I completely ruined the calibration and had to redo the entire 6 hour process again......

Any way to convert the Testek probes oris there a pass through adapter to make the probe coded?
I didn't really appreciate the ingenuity of the coded probes up until I lost it.


Re: 549 transformer question

Dave Wise
 

On page 15 of https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1977-09.pdf? , HP put a damper on a plotter's stepper motor shaft that is an "inertial mass that is free to rotate in a bath of controlled-viscosity silicone oil".


FWIW,

Dave Wise


________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Chuck Harris via groups.io <cfharris=erols.com@groups.io>
Sent: Monday, January 25, 2021 1:49 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 549 transformer question

I am working on it. I have an automated winder designed
and implemented... I still have some problems with wind
quality to resolve.

I use a micro-stepped stepper motor to directly drive the
former upon which the transformer is wound. The problem
is that even though it is micro-stepped 32x, the vibration
of the micro-steps damages the insulation on the wire...
leaving tiny creases every micro-step. The creases are
certain to be points of damage in the insulation integrity,
and are bound to cause arc-overs.

I am working on the problem from two ends, and hopefully
can solve it soon.

The winds the new machine makes are simply beautiful otherwise.

I hesitate to give any predictions, as I have been working
on this winding machine for 7-8 years. Life keeps getting
in the way.

-Chuck Harris


Re: 549 transformer question

Michael A. Terrell
 

Chuck Harris wrote:
Michael,

Flybacks failed, but it was a pretty rare happening
when you consider the massive number of TV's that
were made. I have had dozens of TV sets from the '60s
onward, that never suffered a flyback failure.

What percentage of the sets you serviced got a new flyback?

I would guess less than 1%.

Ask the same question of folks that have scopes that left
the factory with the brown epoxy impregnated HVT's, and I
think you will find 50 to 75% either already have a replaced
HVT, or are nursing one along until someone (hopefully me)
starts winding again.
It wasn't that low. At times it was about one out of 10 sets, and some types failed so often that we kept spares in stock because it could take weeks for any of the parts houses to get them back in stock. I've repaired scopes since the '60s, and the only bad transformer so far was the HV winding in the power transformer of a hobby grade scope. I agree that epoxy isn't a great idea, since the core is magnostrictive, which stresses the covering. That's why the silicone rubber covered TV flybacks were better. It stretched, unlike the wax coating. Later TVs went to a molded plastic housing, sealed with epoxy, and they failed at a higher rate than the silicone rubber types. Add that most of the HV circuit was in the molded box, they were a piss poor penny pinching concept. I only did TV repair until the mid '70s. By that time I was servicing Broadcast and Industrial equipment. Only occasionally a TV at a school. One system had bought a 100 or more Channelmaster TVs that had 84 volts worth of filament string, with what they called a 'Dropping Diode in series. After a year or two the CRTs were quite dim from being powered by a string of DC pulses and other tubes were losing emission as well. I installed a filament transformer in them, and bypassed the original filament windings. There are a lot of bad engineers out there, in the wild. Like you, I want to know what caused a failure, to be sure to check on similar items for the same problems. I despise shotgunning, just to try to save time. Actually finding the bad components improves your troubleshooting abilities on future jobs.


Re: Teitronix 492a : TUNING FAILURE - 1st LO

John Miles
 

One quick correction to my earlier post: if it's a 492A, as opposed to a 492, then you actually can stop the CPU from trying to lock the 1st LO. <SHIFT> FREE RUN should do it.

I don't know if there are any good copes of the 492A service manual floating around on the net, but the 494 / 494P literature is available in the Manuals section at ko4bb.com. It should be fine for troubleshooting the 492A since they were of very similar vintage. Just search volume 1 of the 494 service manual for "TUNING FAILURE" and go from there. There are built-in diagnostic aids that will get you started.

-- john, KE5FX

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Bent Andersen
Sent: Monday, February 08, 2021 11:31 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Teitronix 492a : TUNING FAILURE - 1st LO

HI John

Do you have any idea what I have to do / look for ???? I have check all
voltage and they are ok.

73" OZ1CT Ben


Re: Waking a slumbering 475

Glydeck
 

Ward,

I’m a happy customer of N0DY as well. He’s also a member of TekScopes. Here’s the link to his online store.

https://www.n0dy.com/

George KD6NEW

On Feb 8, 2021, at 2:01 PM, Jeff Dutky <jeff.dutky@gmail.com> wrote:

Ward,

Running the 475 up slowly on a variac is actually one of the performance test procedures, as it will verify that the LOW LINE indicator is working, so if you have a variac and feel like starting the 475 up nice and slow, it will be fine.

The 475 with DM44 does not have a vernier on the delay time position control, rather it has a simple knob (like yours, and as you have seen in pictures): the calibrated delay is, I believe, indicated on the DM44 LED display.

The cord wrap feet do not hold up well over time. I second the recommendation of n0dy-jeff as a source for excellent 3D printed replacements.I have several sets of his cord wrap feet for a couple of 475s and a 475A, and could not be more pleased.

I also have a personal connection to these instruments: my father was a service engineer working on laboratry equipment and data machines, and used a Tek 475 for many years. I have that 475, now 45 years old and still working: it is a wonderful instrument. I have also done some repair and restoration work on the 475 and 475A, and have found it to be enjoyable (if not always easy). I hope you get plenty of enjoyment out of your 475.

-- Jeff Dutky





Re: 485 as a business dependent daily driver?

Ondrej Pavelka
 

I just noticed I haven't replied to your question.
I had few vintage synths with switched mode PSU ringing which caused unreliability of the instrument. I am now happy owner of 2467B and that absolutely nails it. What is but a mere ghost on the 2445B is so well defined bright and sharp on 2467B but that is most likely the brighteye benefit rather then only bandwidth.


Re: 549 transformer question

Mark Vincent
 

Chuck or anyone else with knowledge,

I was wondering if any/some/none of the following could be used in the rewinding of the transformers that might make operation like it should be for a long life. Kapton between the layers, corona dope over layers and GE RTV or similar over the completed core. I did use the RTV under the original white RTV and around the PDA of a crt that the original white had separated from the outer envelope. It now works fine with no corona or arcing. This is the 21kv PDA type crt.

Would increasing the wire size, e.g. 38ga to 36ga, be better for winding(s)? I know the Cu loss would be lower and may be easier to work with being a larger diameter.

By the replies looking for a rewinding source, the one(s) that get a way to rewind the cores that work and hold up would be getting plenty of business. If I had a transformer rewound that the core was too large to allow the filament windings for the 5642s, I would not mind using high voltage solid state diodes. That one modification to have a working scope would be great.

Would Amidon have ferrite cores that would work? I know they make excellent quality products.

These are ideas I threw out to see if any are any good.

Mark


Re: Wrong cable... How bad is it?

Dave Brown
 

Think you meant RG8/12mm - RG6 is 75 ohm.
DaveB, NZ

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jean-Paul
Sent: Tuesday, February 09, 2021 11:10
To: TekScopes@groups.io
Subject: Re: [TekScopes] Wrong cable... How bad is it?

Stephen welcoming to the wonderful world of wired transmission of Signals, researched since the earliest days days of Telegraph, telephone and vidéo.

First, câble Zo is important in a matched system eg 50 ohm cal gen and 50 ohm load.
For audio tests with 1 M Ohm , no difference.

As the frequency, and bandwidth go up, and rise times get short, the Zo is more and more critical to obtaining low reflections, as is the cables VSWR, attenuation and phase vs legnth and frequency.

Thus RG174/u is 50 ohm, but dia ~ 3 mm so rather high atten. db/ meter, while RG58/u, is thicker and RG6/u very thick 12 mm so much mess atten per m thoughts all are 50 Ohm.

For use over 20 MHz eg with SG503 or SG504 or fast pulses like PG506, a calibrated special 1/2 m Tektronix cable is preffered . Generally the shorter the cables the better for cal use.
Finally the wire and insulation quality and connectors precision are factors.

We use the Tektronix and Genrad precision cables for critical applications and avoid the cheap, poorly made Chinese clones.

Suggest that you consult the Belden Wire site papers and applications notes, as well as the detailed specifications on whatever cables, connectors and wire you use.

Bon courage

Jon


Re: 2465B CTT options board faults

Jean-Paul
 

Dear Chuck many thanks again, especially the warnings re crippled hybrides on epay.

As I have four others open at the moment that work I have fourth chances to find a working trigger hybrid.
I shall check for 100% CTT operation and all tests on two other CTT working units, then try swapping out, for a known good one.

What fun!

Enjoy

Jon


Re: Wrong cable... How bad is it?

G Hopper
 

This is an interesting thread since I, like Stephen, have long assumed my
cables were ok. I'm no longer 100% sure and need to check them.

However, what REALLY caught my attention was Jon's comment "For use over 20
MHz eg with SG503 or SG504 or fast pulses like PG506, a calibrated
special 1/2 m Tektronix cable is preffered..."

Having one of those devices, and not having the special cable, what's the
solution?

Is the solution to the issue: getting/building a cable (with 50 ohm coax)
of exactly 1/2m length? or is it something else? There must be a solution
other than acquiring an original cable since Tektronix would have had a
specification and had cables made to that spec. I've got to believe that
it's something that mere mortals can reproduce. :-)

If it is, where can one gather the information?

Cheers,
Grant

On Mon, Feb 8, 2021 at 2:09 PM Jean-Paul <jonpaul@ix.netcom.com> wrote:

Stephen welcoming to the wonderful world of wired transmission of Signals,
researched since the earliest days days of Telegraph, telephone and vidéo.

First, câble Zo is important in a matched system eg 50 ohm cal gen and 50
ohm load.
For audio tests with 1 M Ohm , no difference.

As the frequency, and bandwidth go up, and rise times get short, the Zo
is more and more critical to obtaining low reflections, as is the cables
VSWR, attenuation and phase vs legnth and frequency.

Thus RG174/u is 50 ohm, but dia ~ 3 mm so rather high atten. db/ meter,
while RG58/u, is thicker and RG6/u very thick 12 mm so much mess atten per
m thoughts all are 50 Ohm.

For use over 20 MHz eg with SG503 or SG504 or fast pulses like PG506, a
calibrated special 1/2 m Tektronix cable is preffered . Generally the
shorter the cables the better for cal use.
Finally the wire and insulation quality and connectors precision are
factors.

We use the Tektronix and Genrad precision cables for critical applications
and avoid the cheap, poorly made Chinese clones.

Suggest that you consult the Belden Wire site papers and applications
notes, as well as the detailed specifications on whatever cables,
connectors and wire you use.

Bon courage

Jon









Re: 2465B CH1,2 compression

Jean-Paul
 

Dear Chuck as always perfect information and exactly right.

I will go through swapping the hybrids, later this week.

Kind Regards

Jon


Re: Wrong cable... How bad is it?

Jean-Paul
 

Stephen welcoming to the wonderful world of wired transmission of Signals, researched since the earliest days days of Telegraph, telephone and vidéo.

First, câble Zo is important in a matched system eg 50 ohm cal gen and 50 ohm load.
For audio tests with 1 M Ohm , no difference.

As the frequency, and bandwidth go up, and rise times get short, the Zo is more and more critical to obtaining low reflections, as is the cables VSWR, attenuation and phase vs legnth and frequency.

Thus RG174/u is 50 ohm, but dia ~ 3 mm so rather high atten. db/ meter, while RG58/u, is thicker and RG6/u very thick 12 mm so much mess atten per m thoughts all are 50 Ohm.

For use over 20 MHz eg with SG503 or SG504 or fast pulses like PG506, a calibrated special 1/2 m Tektronix cable is preffered . Generally the shorter the cables the better for cal use.
Finally the wire and insulation quality and connectors precision are factors.

We use the Tektronix and Genrad precision cables for critical applications and avoid the cheap, poorly made Chinese clones.

Suggest that you consult the Belden Wire site papers and applications notes, as well as the detailed specifications on whatever cables, connectors and wire you use.

Bon courage

Jon


Re: 3T77A manual and mildew issue

 

Turns out the 3T77A change information (which is considerable) is part of the online 3T77 manual. So I'm good there.

The white specks on the outside of the capacitor sleeves wipe off with alcohol and swabbing, but the ink has migrated into the plastic sleeve so I can't read values. The only one that looks like it should definitely be replaced is the large 250 uF power supply filter cap (the red rubber seal has what looks like a burned spot pushed from the inside). More as I have time to play with it!


485 and 7904A serial numbers

n49ex
 

I have a 485 and 7904A that are in pristine condition. Both have B (Beaverton) serial numbers. Is there any place you can find what the last serial numbers produced are for either one of these? I've had, fixed and sold many 485s, and this one has the highest S/N I've ever seen - wondering how close to the last it is....

Reinhard

6601 - 6620 of 184565