Date   

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.


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

demianm_1
 

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.


Re: 549 transformer question

greenboxmaven
 

As a long ago veteran of the TV repair craft, flybacks rarely failed without some other circuit or component failure or very adverse operating conditions. How many times has anyone seen carbonized cockroaches shorting out and frying a Tektronix HV transformer? Or, a horizontal output tube lose drive and truly melt down taking the flyback with it? Color sets were worse, with the higher voltages and much higher beam current and deflection power needed.

Bruce Gentry, KA2IVY

On 2/8/21 16:09, 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.

-Chuck Harris










Re: Extracting a buggered knob grubscrew

snapdiode
 

On Sun, Feb 7, 2021 at 11:29 PM, Paul McClay wrote:

1.27 & 1.3 mm drivers... if they actually differ by 0.03 mm that would suggest goodness indeed.

AFAICT, yes, these tools are accurate in their description. I'm no expert, but several measurements with a caliper do show a slight difference.


Re: Extracting a buggered knob grubscrew

Chuck Harris <cfharris@...>
 

I like PBBlaster, but one thing I have noticed is any
bolt/nut I use PBBlaster on, will be badly corroded the
next time I visit it. I would recommend washing it away
thoroughly.

The acetone in Ed's Red will be gone before you can say
Bob's your uncle. Its sole and only purpose is to bring
the transmission fluid into the threads, or under the
copper/lead fouling in the case of guns. It evaporates
very, very quickly.

-Chuck Harris

- wrote:

You don't have to bath it in oil but a good PENETRATING oil will creep.
But I agree with you that there are good ready made solvents that won't
harm the plastics and my preference would be to use one of them instead of
something that I don't know would be safe.

I have a 5 gallon can of home made Ed Red's sitting in my garage. Great
stuff! But I used PB Blaster to loosen the set screws on my 576. A tiny
drop applied with a toothpick is all that is needed.

On Mon, Feb 8, 2021 at 10:09 AM Chuck Harris <cfharris@erols.com> wrote:

You don't have to bathe the entire knob in the stuff, you know.

Kroil, PBBlaster, and other penetrating oils contain good stuff
that I wouldn't want to soak a plastic knob in either.

The Acetone/ATF mixture, is based on a homemade gun cleaner known
as Ed's Red, and has been shown to beat all of the commercial
penetrating oils at reducing fastener breakaway torque, when applied
to the exposed threaded area of the fastener.

But, YMMV.

-Chuck Harris

- wrote:
That's a good mix for working on mechanical stuff but I don't think
I'd
be willing to try Acetone on a Tektronix knob or painted surface. ATF
fluid
by itself is a good penetrating oil and is *probably* safe and effective.
But I still wouldn't use it on anything that is irreplaceable until I
knew
that it was safe.

On Mon, Feb 8, 2021 at 12:15 AM Frank DuVal via groups.io <corvairduval=
netscape.net@groups.io> wrote:

Kroil is excellent.

But also try 50/50 mix of ATF and Acetone. That's any automatic
transmission fluid and Acetone.

Of course if you have to buy a quart of fluid and a quart of Acetone,
one can of Kroil may be cheaper if available locally.

Frank DuVal

On 2/2/2021 4:44 PM, JJ wrote:
I used a drop of Kroil on a 7000 plugin knob set screw when it was
frozen.
That stuff never lets me down. Of course, you need to use it before you
strip the screw head! And, you need to be patient - like a few drops
over
an 8 hour period. Be careful that you don't get the stuff on the face
of
a
Tek instrument - it will likely take the print off. But, just about
anything other than a lightly water damped cloth will take the print
off
a
Tek instrument.

JJ


















Re: 2465B CTT options board faults

Chuck Harris <cfharris@...>
 

I just finished remotely helping a friend with his scope,
and was getting my confidence pretty well shaken when two
trigger hybrids both failed. It took a third, this time
from our friend in Greece, to fix the problem.

As I said earlier, there is a booming business in selling
almost good trigger hybrids on ebay.

The CTT and the automatic frequency measurement both use
a function in the trigger hybrid that isn't used by any other
scope function.

A perfectly performing scope can have a trigger hybrid that
won't measure frequency, or work with the CTT.

I wish I could say that just replace this part or tweak that
pot, and your hybrid will come back to life, but I haven't
figured out what that part is, or where that pot resides...

-Chuck Harris

Jean-Paul wrote:

Dear Chuck: Many thanks

I had tested the U500 trigger hybrid by exchanging for another from ebay (got two for $30) not from our friend Alex.

Neither of the exchanges made any difference.


Instead I should use a known good scope with working CTT . I can also swap out the option board of a know good CTT.

All the Best,

Jon









Re: 2465B CH1,2 compression

Chuck Harris <cfharris@...>
 

Hi Jon,

The calibration routine compensates for the gain of the
CH1 and CH2 preamp/attenuators, and adjusts a bias level
to aid the transient performance, but there is nothing
in the stored calibration data that would prevent a scope
from displaying a waveform with pretty good fidelity.

-Chuck Harris

Jean-Paul wrote:

Dear Chuck rebonjour,

I thought so, and tested CH2 out at rear panel BNC, direct from CH2 preamp hybrid, it was perfect.

Before I pay $120 or more for the channel switch hybrid, I will swap out from a know working scope.

My other point: In the CAL procedure is there a vert CAL that somehow affects bias or other voltage dependent parameters in this hybrid? If yes can this be an off CAL symptom: I am using a swapped A5 at the moment with definitely wrong CAL parameters.

I really need a parts donor 2465B!

Jon






Re: 549 transformer question

Chuck Harris <cfharris@...>
 

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.

-Chuck Harris



Michael A. Terrell wrote:

Chuck Harris wrote:
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.






Tektronix 2213A teardown ("1980's Cathode Ray Oscilloscope Teardown")

Ke-Fong Lin
 

Hi everyone,

Element 14 youtube channel made a video that may be of interest to you guys:

https://youtu.be/QkgtF6BLy2A

Enjoy! :)

Best regards

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