Date   

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


Re: Waking a slumbering 475

 

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: Wrong cable... How bad is it?

Stephen
 

On Mon, Feb 8, 2021 at 10:39 AM, demianm_1 wrote:


It depends on what you are calibrating for. If it was a VNA I would say start
over.. For a scope and a short cable you may see some odd overshoot but in
typical use the scope input is 1 Meg and the cable is short so it may have no
impact. Check between a 50 Ohm and a 75 Ohm cable and see if you do see a
difference in what you are looking at.
No VNA´s, just Tek scopes when the procedures ask for a 50ohm cable.
The cables I used are relatively short, about 1m long actually, or about 40´´.
If I have to go through everything again, that would be bad...


Re: 3T77A manual and mildew issue

unclebanjoman
 

Hi Charles,
I own both 3t77 and 3t77a, in perfectly working state.
I have the original 3t77 manual but never I found the 3t77a manual.
However there is a copy of the 3t77 manual with added 12 pages of manual change information regarding the 3T77A version that explain very well the differences and the adjustment procedures. There are the schematic changes also.
You can find it here: http://bama.edebris.com/download/tek/3t77/3t77.djvu
It is in djvu format, not as usual as pdf, but easily readable for example, with IrfanView

Max


Re: 549 transformer question

Tom Lee
 

Hi Michael,

I think you meant to say that 807s were used in early B&W sets, not color ones. The 6BG6 was very popular in the early sets, and was basically an 807 in octal form.

Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

On Feb 8, 2021, at 9:45 AM, Michael A. Terrell <terrell.michael.a@gmail.com> wrote:

Chuck Harris wrote:
Hi Dave,

I have thought about this over the last several days, and you
are probably right. I never tested my conjecture, it was just
an inkling that I had.

Tektronix wasn't a stupid company, they did things usually
for good reason. I am sure they used sine wave oscillators for
HV production because they were in the transient measurement
business, and knew a slew of 50KHz high voltage flyback harmonics
would be just too darn much fun to suppress, so they settled for
an easier to filter, more harmonic free sine wave approach.

And, yet, I have still pondered their choice for quite a few
years. Mostly, because it also appears to have been one born
of expedience.

I don't suppose I would have ever even pondered the HV section
of tektronix scopes, had they just worked. I certainly never
did until I was introduced to a pair of time worn 545B and 547
scopes that entered my collection.

And yet, as smart as Tektronix was, they had a host of HVT failures
when the TV set manufacturers didn't. And it took them 10 years
of seemingly fumbling around to come up with a solution.
Chuck, TVs had a lot of bad fybacks, often burnt to a crisp. The early, wax sealed were the worst. The heat they generated would cause the coating to deform, and if the home wasn't air conditioned you would find drops of wax on the floor, under he set on some models. They were a lot more reliable after the switched to the silicone rubber molded designs, but it wasn't unusual to have to modify a chassis because the OEM had to redesign a flyback. A couple GE color flybacks came in a new steel subchassis, because there were so many differences. Spring and fall in S.W. Ohio had the highest failure rate, in homes with people who smoked. Nicotine would cover the outside of the CRT, increasing the load on the Second Anode supply. We saw about 90% of the failures during these times as the humidity spiked, making the nicotine more conductive.

BTW, the first color TVs used the venerable 807 tube for the Horizontal output tube. I laugh when hams deride using 'sweep tubes' for RF, when they started out as improved versions of the 807. The first change was to re-base it from a five pin base to an octal base.





Re: Waking a slumbering 475

Keith
 

You can get replacement feet from a guy on eBay by the name of n0dy-jeff based in southern CA. I've had a set each for my 465B and 475, as the originals go crumbly with age.

Scuffing to the display is probably to the perspex screen cover - I've used some stuff called Novus Acrylic Scratch Remover & Cleaner to get light marking/scuffing off. It takes a good deal of buffing but does seem to work.

As for the delay time knob, my 465B which I've had since 1995 has just a Tek plastic knob, whereas the 475 has the vernier one. Both look like they've been on since new but who knows.

As to whether you should run it up on a variac, I'll leave that to the jury; I tend to on old valve stuff and anything I'm uneasy with. So far I've not had exploding tantalums though.

8521 - 8540 of 186480