Date   

Waking a slumbering 475

Weathers, W
 

Greetings all,

I picked up a Tek 475 with the DM44 option installed. It came with an
HP 10433A 10:1 probe marked "10MOhm // 10pF For 1MOhm // 10-16pF
inputs" (an apparent mismatch for the 475's 20pF input). No scope
manual was included with the sale, unfortunately. I know they can be
downloaded, but I'd like a printed copy. I have been perusing the
electronic copy.

The previous owner said the scope worked when he last used it. It has
been stored in a basement for a number of years. The P.O. had
recently powered it on to verify beam presence and trace on both
channels. I don't think much more has been done to it. And I don't
think it was powered on for very long.

First, a visual condition check:

The case looks to be in good condition. All knobs look to be present,
intact, and operable. The focus knob turns a little hesitantly
compared with the others, but that might be normal. A couple of the
Vertical Mode buttons show deterioration of the silk screen (the Add
and Chop buttons). The Delay Time Position knob is not a metal
graduated vernier knob but instead is an unmarked plastic knob. A
quick search shows similar knobs on some 475s out in the wild, so I
presume this is not the result of a replacement by owner.

The positive jack on the DM44 is loose.

One of the cord-wrap feet has damage to the lower-most cord channel.

There is some scuffing to the display that isn't noticeable when
looking at it head on, but can be seen at an angle. It's almost looks
as if somebody traced a noisy trace onto paper.

The manual/probe pouch smells a bit musty.

Before I do much with this 475, I thought I would check in here so
that I don't inadvertently rudely awaken it and let the smoke out.
How can I best gently wake it up? Are there best prophylactic
practices? I searched here but haven't turned up anything. I am sure
this information exists in the vast body of posts here,but I am having
trouble surfacing it.

This is the first oscilloscope that I have personally owned. I have
used both digital and analog scopes, the vast majority by Tek, though
I have never dug into one.

I am aware that these old scopes have tantalum capacitors that like to
short out. I am also aware that, in general, old electrolytics tend
to be dodgy. Do I need to throw this thing on a variac? And given
that this scope has been a basement queen, I am wondering if something
should be done to address the possibility of long term humidity
effects.

Scopes from the 475 era have a particular personal connection for me,
as my father was a Tektronix veteran. He was a technical writer for
Tek for 20+ years, spanning the 60s and 70s and into the very early
80s. He and his team produced the manuals for oscilloscopes and other
Tek products. If there are any old Tek employees from that era
reading this, yes, my Dad was Stormy.

Ward Weathers


TDS510 or TDS460A or 485 scopes as upgrade

Giuseppe Marullo
 

Hi all,
just joined.

Owner of a Rigol 1054z, satisfied user for what I am currently doing (especially for the price!) .

Being a 50/100MHz with 1Gs/s bw scope, I wanted to explore other options to increase visibility of higher frequencies, and glitches.

Would a TDS510 or TDS460A be a big improvement?

I don't understand if they are also a higher analog bandwidth/analog scope or it is just the sampling that makes them display higher frequencies (periodic waveforms?). They can reach greater vertical resolution if I understand correctly.

Or should I stick to old good 350MHz like Tektronix 485 (just analog)?

I am not interested in digitizing the waveform, even though a GPIB dump of the screen would be nice (but for lower frequencies the 1054z does it nicely).

Budget is tight, not for professional use, second hand offering in EU is limited compared to US.

Thanks in advance.

Giuseppe Marullo
IW2JWW - JN45RQ


Wrong cable... How bad is it?

Stephen
 

I’ve just realized that for a long time I’ve been using 75ohm-20’´ long coax for my calibration procedures are for mostly everything when coax cables are required.
I trusted the place I bought these from, because I specifically asked for 50ohm ones. I never bothered to check. But for some reason today, while replacing a bad BNC connector one one of them, I was stunned when I read 75ohm on the wire.
So how bad is it as far as all my calibration procedures? Do I have to go over everything again on my 10+ scopes!?!?


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

Bent Andersen
 

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: 3T77A manual and mildew issue

-
 

The OLD paper bodied caps were often coated in bee's wax. That might be
the culprit.

On Mon, Feb 8, 2021 at 12:36 PM Charles <charlesmorris800@centurytel.net>
wrote:

Does anyone know where I can download a copy of a 3T77A (not 3T77) manual?

Also, any idea as to what could cause this kind of mold/mildew on only
the axial electrolytic caps, and no other components? Storage humidity?
The other components all look like new except for that weird white
speckling on every one of the caps (and the deteriorated paper jacket on
the large cap)...

I tried to include a pic but got an error that the group does not accept
attachments.

thanks

Charles







Re: 549 transformer question

Michael A. Terrell
 

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.


3T77A manual and mildew issue

 

Does anyone know where I can download a copy of a 3T77A (not 3T77) manual?

Also, any idea as to what could cause this kind of mold/mildew on only the axial electrolytic caps, and no other components? Storage humidity? The other components all look like new except for that weird white speckling on every one of the caps (and the deteriorated paper jacket on the large cap)...

I tried to include a pic but got an error that the group does not accept attachments.

thanks

Charles


Re: Sick SG504

Dick
 

Look at the TinySA now on the market, but be wary of
the numerous clones that may or may not work.

The ones at R&L seem to be OK.

73, Dick, W1KSZ
________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Eric <ericsp@gmail.com>
Sent: Monday, February 8, 2021 10:23 AM
To: TekScopes@groups.io <TekScopes@groups.io>
Subject: Re: [TekScopes] Sick SG504

Thanks John I will check this out tonight. I have a spec an in the lab but it currently tops out at 40 Mhz. So it looks like I will need to go a touch faster. Ill see what I can find have any recommendations in the Spec an department. I am very much out of my depth there but I am learning as fast as I can.

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of John Bennett
Sent: Monday, February 8, 2021 11:36 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Sick SG504

The high side buffer amplifier (Q70) is the most likely suspect. This is a TO128 NPN transistor, Tek part number 151-0474-01. There are several suitable replacements from the cable industry, but the cost effective BFR94A works fine. Be sure you are ordering the TO128 (studded) package, as the NXP variant is an SOT23.
Also check to see if Q70 is getting drive at its base. If not, there is a small carbon composition resistor inside the high frequency cavity oscillator that sometimes cooks itself to death. I forget it's value, but if you open up the HF cavity (the one to the rear) this is easy to check and replace (with care).
Far less likely to fail are the HF series and shunt diodes, CR80, and CR155, CR158, & CR160, respectively.
After repair, the unit will need a recal, particularly the HF harmonic suppression and leveling step (you will need a spectrum analyzer).
73,
John Bennett
AE0AM


Re: Sick SG504

Eric
 

Thanks John I will check this out tonight. I have a spec an in the lab but it currently tops out at 40 Mhz. So it looks like I will need to go a touch faster. Ill see what I can find have any recommendations in the Spec an department. I am very much out of my depth there but I am learning as fast as I can.

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of John Bennett
Sent: Monday, February 8, 2021 11:36 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Sick SG504

The high side buffer amplifier (Q70) is the most likely suspect. This is a TO128 NPN transistor, Tek part number 151-0474-01. There are several suitable replacements from the cable industry, but the cost effective BFR94A works fine. Be sure you are ordering the TO128 (studded) package, as the NXP variant is an SOT23.
Also check to see if Q70 is getting drive at its base. If not, there is a small carbon composition resistor inside the high frequency cavity oscillator that sometimes cooks itself to death. I forget it's value, but if you open up the HF cavity (the one to the rear) this is easy to check and replace (with care).
Far less likely to fail are the HF series and shunt diodes, CR80, and CR155, CR158, & CR160, respectively.
After repair, the unit will need a recal, particularly the HF harmonic suppression and leveling step (you will need a spectrum analyzer).
73,
John Bennett
AE0AM


Re: 549 transformer question

Jean-Paul
 

Rebonjour Roger and all,

1/ the typical failure is hairline cracking résulting in entry of air, which then ionizes, eventually causing a,carbon track along the crack surface.

Another failure mechanism is entrapment of air bubbles due to lack of vacuum, or insuffisant time, temp, annealing.

2/ The plotting material and process was propriétaire and cost perhaps $50 eack in volunteer production, minimum was 100-1000 per run!

3/ My HV potting work was 1980s...1990s. Even if I knew what the material was, I have forgotten and lost the old documents.

Nonetheless I shell search my archives and pass on any tips.

Best Regards

Jon


Re: 549 transformer question

Chuck Harris <cfharris@...>
 

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.

Yes, I know, flybacks do fail; but, they were a much harder design
problem, making at least 18KV from their winding. Tektronix only had
to make an HVT that could handle 2.5KV.

My inkling was born of the thought that both markets should have
used similar materials during similar timeframes, and suffered
similar problems, but only the tektronix sine wave oscillator based
HVT's seemed to fail so destructively.

But I haven't tested my conjecture, so you are probably right.

-Chuck Harris

Dave Wise wrote:

?I have to disagree, Chuck. While epoxy loss may stop a Hartley, that's just the way loss manifests in that circuit. In my 453, which is not a Hartley, the oscillator biased up harder and harder trying to maintain output voltage, eventually blowing the fuse, but it oscillated right to the end. I believe a MOPA or flyback would have done the same.


Regards,

Dave Wise

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Chuck Harris via groups.io <cfharris=erols.com@groups.io>
Sent: Saturday, February 06, 2021 8:08 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 549 transformer question

I think the biggest reason that tektronix suffered
so much with the epoxy disease is their use of the
transformer as the tank circuit in a Hartley
oscillator.

If they had used the more usual flyback configuration,
or a MOPA configuration, they probably would have never
experienced the problem. The transformers would have
gotten a little hotter, but would have kept on keeping
on. Eventually they would dry out, and as long as the
scope was getting used, they would be good.

Using the transformer as a tank for an oscillator made
the transformer losses reduce the effective gain of the
feedback circuit, and allowed the oscillator to quit.

-Chuck Harris

Jean-Paul wrote:
Chuck: I had no idea of this longstanding problem. In 1970s...1990s we designed and manufactured HV, SMPS, medical and avionics transformers, and potted small HV power supplies.

1/ The potting process of HV parts and transformers is very tricky as epoxies cause mechanical stress and are chemically active as they cure.
The thicker the cross section of the encapsulant the worse the stresses become.
We potted ~ 1" x 0.75" x 3" with tiny RM-6 HV transf and 13 stage HV multiplier. Yield was only ~ 30-50% at first.
It took ONE YEAR to refine the material and process to get ~ 95% yield.

2/ The best epoxies are highly filled, low TC and heat + catalyst cure.
Tiny bubbles entrapped will ionize and eventually fail. The windings can be protected with cloth tape, silicone precoat, etc.
A vacuum oven is essential to remove entrapped air and to cure. After cure, they parts are gradually returned to room tem , during some hours or days to anneal the epoxy.

3/ Many winding machines are still manufactured, USA Adams-Maxwell, Stevens Industries and in Switzerland, MicaFil, and the usual Chinese knockoffs.
Most are layer wind machines and do not have a universal wind.
Accessories include automatic transverse and tensioners for fine wire. Besides steppers, they are mechanical screw operated like a lathe.

4/ layer wind sectionalized and universal winding techniques give very different capacitance and self resonant frequency.

5/ Wire choice is critical, type of insulation and number of layers of insulation. We used #36..#39 with double triple and even quadruple build solderable (Solderease, Nylease).

I have machines and equipment but have not vacuum ovens, as we no longer manufacture these HV parts.

Happy to send you (on the forum or PM) more info.

Best Regards,

Jon


















Re: 549 transformer question

Gordon Smith
 

On Sun, Feb 7, 2021 at 12:57 PM, Joel B Walker wrote:


Is that part number 120-0275-00 for the 564 HV transformer?
Yes. But don't get a transformer from a 564B. That part # is 120-0466-00 and is potted with epoxy.


Re: Sick SG504

John Bennett
 

The high side buffer amplifier (Q70) is the most likely suspect. This is a TO128 NPN transistor, Tek part number 151-0474-01. There are several suitable replacements from the cable industry, but the cost effective BFR94A works fine. Be sure you are ordering the TO128 (studded) package, as the NXP variant is an SOT23.
Also check to see if Q70 is getting drive at its base. If not, there is a small carbon composition resistor inside the high frequency cavity oscillator that sometimes cooks itself to death. I forget it's value, but if you open up the HF cavity (the one to the rear) this is easy to check and replace (with care).
Far less likely to fail are the HF series and shunt diodes, CR80, and CR155, CR158, & CR160, respectively.
After repair, the unit will need a recal, particularly the HF harmonic suppression and leveling step (you will need a spectrum analyzer).
73,
John Bennett
AE0AM


Re: 2465B CH1,2 compression

Jean-Paul
 

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: 2465B CTT options board faults

Jean-Paul
 

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: Help for DC503A universal counter repair

Attilio
 

Hi everyone,
sorry but i probably didn't understand how PERIOD B and PERIOD B AVG work. From more in-depth tests I have understood that it is possible to use PERIOD B to measure medium-long periods (example 100 ms) while the PERIOD B AVG (average) can be used to measure short periods (example 100 ns). Am I wrong or does it work like this?

The problem of blanking remains, solved for now by disconnecting pin 11 of the U1520 (LS7031), but in this way the leading zeroes remain on.

-- Cheers
Attilio


Re: Extracting a buggered knob grubscrew

-
 

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 CH1,2 compression

Chuck Harris <cfharris@...>
 

Channel switch hybrids, and trigger hybrids are the two most
common hybrid failures on this scope, in my experience.

CH1 and CH2 are the only channels the readout steals time from,
CH3 and CH4 are left alone.

Some strange channel dependent failures can be traced to the
transistor array chips used to condition the CH5 readout stuff,
but probably not in this case.

I would try a different channel switch hybrid first. It is
always good to have a scope on hand to swap parts.

-Chuck Harris

Jean-Paul wrote:

Rebonjour a tous:
Same low SN B062 2465B
has extrême CH1,2 compression on lower part of display.

CH 3, 4 are perfect and normal.

Photo Album: 2465B CH1,2 compression

Taken with 100 kHz triangle on CH 1 and CH2,
position upper nearly linear position lower screen, extreme compression and non linearity.
Transient response is also severely affected as position of traces is moved.

1/ all PSU voltages normal,

2/ using substitute A5 so no CAL data is valid.

3/ Is there an adjustment or bias eg on U400 channel sw ?

4/ Pulled U400, cleaned the hybrid contacts, no change

is there a place to test signals into U400 from CH 1,2 preamp U100, U200?

Assume U400 155-0236-00 is bad and replace (VERY costly!)

Many thanks

Jon







Re: Extracting a buggered knob grubscrew

Chuck Harris <cfharris@...>
 

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: Tektronix 7b92a shuts down crt & graticule illumination on 7904 mainframe

n49ex
 

Great story Stephen, and great ending to the 7B92A repair! Now, if you want to up the anti for your collection, keep an eye out for a 7904A - they are of course newer, and have a bunch of little improvements on the classic design.

Since you said you also have a 2465A, (I have one too, as well as a 2467A, another Tek masterpiece) a site to be aware of is Dr. Hugo Holden's electronics page, http://worldphaco.com/
He has some wonderful papers on 2465A repairs, including dealing with the eventual failures of the clock/memory chip, electrolytic leakage damage repair, etc.

Cheers!

Reinhard MetzBell Labs retired

6881 - 6900 of 184812