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-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of lop pol via Groups.Io
Sent: 02 November 2018 16:21
To: [email protected]
Subject: Re: [TekScopes] N channel fet 151-1121-00 -- V10206

After messing around this is the trace I get.

/g/TekScopes/photo/77313/0?p=Name,,,20,1,0,0

check the side of the case there may be "holes" for some of the sensitive
adjustments. there are on a 475 and the case needs to be installed for those
adjustments.
搁别苍é别

On 2018-11-02 5:34 a.m., Chuck Harris wrote:

Definitely not normal! If tektronix needed you to put a special
shield there, there would be a shield with a part number specified
in the list of things required for calibration.

Definitely not normal! If tektronix needed you to put a special
shield there, there would be a shield with a part number specified
in the list of things required for calibration.

What you have is probably a point grounded by a screw that has corroded,
a bypass cap that is sub-optimal, or possibly an active part that has
gotten wild.. look for a replacement part that has too much gain to be
stable in the circuit, too long leads, needs a ferrite bead...

Also look for socket pins on active parts that are marginal.

-Chuck Harris

Jeff Urban wrote:

AHA !

/g/TekScopes/photo/77251/1?p=Name,,,20,1,0,0

That is a piece of blank PC board on the left there grounded by a clip lead. The trace is smaller than it looks in the picture, I probably should've turned the intensity down but it's pretty clean from here.

If that is normal for having the cover off, how do you work on the vertical front end in these things ? How do you even begin to calibrate it ?

Enquiring and hopeless minds want to know.

It is a day.

On Fri, Nov 2, 2018 at 11:59 AM, Jeff Urban wrote:

If that is normal for having the cover off, how do you work on the vertical
front end in these things ? How do you even begin to calibrate it ?

No, it is not normal although the area is sensitive to external signals, like hum; you're covering and grounding a high-impedance part of the vertical input amp, directly after the attenuator block with attenuation set at 200 mV/div.
Are you sure there's no external source producing something like 50 kHz, if I'm reading the horizontal settings correctly?

Raymond

AHA !

/g/TekScopes/photo/77251/1?p=Name,,,20,1,0,0

That is a piece of blank PC board on the left there grounded by a clip lead. The trace is smaller than it looks in the picture, I probably should've turned the intensity down but it's pretty clean from here.

If that is normal for having the cover off, how do you work on the vertical front end in these things ? How do you even begin to calibrate it ?

Enquiring and hopeless minds want to know.

It is a day.

Or, you could just slide the blue filter up, and out at the bottom
and remove it. The gorp might be just there.

-Chuck Harris

David Kuhn wrote:

Craig,

Thank you kindly for those detailed instruction, which I have printed

out.

Perhaps later today, I will follow them and get that puppy cleaned out

and

generally look inside for cap leakage.

Dave

On Thu, Nov 1, 2018 at 10:54 AM Craig Cramb <electronixtoolbox@...

wrote:

The knobs don’t have to come off. This is how I do it all the time. I
usually take the case off when doing this but the scope needs a front

cover

which you may not have. But it if you set the face on carpet and

carefully

and don’t put alott of pressure on the controls of the front panel.

Remove

On Wed, Oct 31, 2018 at 06:22 PM, Jack wrote:
Hi...and thanks for the offer towards the end of your letter Fabio...I sent
in what I presume to be the correct 'slot', {Ou pergunte ao
vendedor...Escreva uma pergunta... }

this as follows:

Hi I need a vertical Amplifier (complete module) for a Tektronix M
425....do you have a low mileage; unit? My Regards Tony,.....
goldmort@onthenet,com.au.

Hola, necesito un amplificador vertical (módulo completo) para un Tektronix
M 425 ... ?tiene poco kilometraje? ?unidad? Mis saludos Tony, goldmort @
onthenet, com.au


Oi eu preciso de um amplificador vertical (módulo completo) para um
Tektronix M 425 .... você tem uma baixa quilometragem; unidade? Meus
cumprimentos
Tony, goldmort @ onthenet, com.au

Hopefully the Google translations do not see him lying on the ground
laughing and crying at the same time!!

Warm Regards Fabio
Jack

-----Original Message-----
From: Bert Haskins
Sent: Thursday, November 1, 2018 6:30 AM
To: [email protected]
Subject: Re: [TekScopes] 425 Mil vertical module needed....seeking



On 10/31/2018 11:56 AM, Fabio Trevisan wrote:

Hello Jack,

What you refer to as 425 Mil is, for correctness sake, a 465M or an AN/USM
425.
It confused me at first, as I didn't recall there was ever a 425
oscilloscope.
For what I know, the 465M is electronically similar to the civilian 465
(but even at electronic diagram level, there ARE differences), but, for
the sake of assemblies or sub-assemblies, they're essentially two
completely different oscilloscopes (i.e the boards are physically
different).

As mentioned on this () page of the
TekWiki website, the 465M is more similar to the civilian 455, than it is
to the 465.
I can't really tell by how much they are similar, but you may be able to
compare them by yourself by looking at the service manuals of both, which
are available on the TekWiki website.
The page for the civilian 455 is here:

I don't know much of either (455 or 465M) but, coincidentally, there's a
seller on a Brazilian auction site, selling the modules of a Tektronix
455:

I can't tell how similar those modules are (to your 465M) and if they can
serve as parts donors, but if you find out that they may help, you can try
to contact the seller, or I can help you with the purchase and shipping of
the module (or the parts) to your location, for their advertised cost and
shipping expenses to your place.

Note: I have no affiliation with the seller (and don't even know if I know
them, since the auction site only reveals the seller after you purchase
the item).

I normally wouldn't even make this offer, as shipping from Brazil is
usually prohibitive and the parts are not even mine... But since you're so
far away down under, I think that shipping from anywhere will be just as
difficult.

Please let me know if you want my help, or maybe some other folks in the
group will chime.

Krgrds,

Fabio






On Tue, Oct 30, 2018 at 06:52 PM, Jack wrote:

Hi. I'm a new member finding my way. I bought a lot of Tektronix scopes
for
the services when with Defence during Vietnam era and visited Tektonix at
North Ryde (NSW)
to see about repairs to (I think it's a 564) I still have....still not
working
I guess after having a new very high voltage insulated transformer wound
for
CRT filament...two actually, the other must be around "somewhere". I
developed a healthy fear of Tektronic CRO's owing to the prices Tektronix
charged for repairs..

I have a 425 Mil with broken switch.in Vertical section It's
unrepairable.
Whilst I could sooner or later find a parts CRO, sight unseen on eBay for
example, it may also be on the way out. I think the plastic used in
Tektronix
may be the lowest quality amongst high quality devices , or maybe they
just
specify 'shall be or a type formula and manufacture which will maintain
all
utility until the end of time'

I was directed to your group (Hi...there) . To get to the essential point
Would some person have a reasonably low mileage vertical module,
complete,
which I could buy? Please advise me if so....Australia would be best of
course
but 'anywhere'. Also...to undo some confusion...I've been told 425 and
465 are
"intrinsically" the same CRO...obviously without the Mil labelling... .
Does
that mean parts are interchangeable?

One reason I ask is that I was also told that the 425 being Military
contract
and Mil Spec was built to be readily pulled down for field repairs. Is
that
true?...Is that a quality the 465 does not replicate? if so it may mean
that
...just as an example...the vertical amp module from a 465 may have some
mounting differences from the 425.

On the other hand it may not. Perhaps someone familiar with this type
will
bring me to a state of awareness even wisdom regarding my CRO. ...oh...
other
than having one channel down it seems to work ok and 'oh' again...when I
originally pulled it down a piece of curved springy metal fell out.
Whence it
exactly originated I have no idea...'somewhere inside'. .It may be a
method
of maintaining the case at frame potential, under pressure as one
reassembles
the CRO...so perhaps it 'jammed' between a plate on the chassis and the
bottom cover. It could have come from elsewhere or it might not be from
the
CRO at all.....That said, Im pretty sure I saw an exploded view one time
where
this curved metal piece as shown hanging in mid-air underneath the
chassis.
Have I been able to find that particular exploded view again (that was 3
years
ago)...of course not!!

Any passing of knowledge wisdom common sense mindfulness and most of all
perhaps a complete vertical amplifier will be very well received.
--
Jack

I have a 465M vertical module I bought as a backup.
NOS but not tested within the last five years or more.

Thanks,
Bert

--
Jack

Craig,

Thank you kindly for those detailed instruction, which I have printed out.
Perhaps later today, I will follow them and get that puppy cleaned out and
generally look inside for cap leakage.

Dave

On Thu, Nov 1, 2018 at 10:54 AM Craig Cramb <electronixtoolbox@...>
wrote:

The knobs don’t have to come off. This is how I do it all the time. I
usually take the case off when doing this but the scope needs a front cover
which you may not have. But it if you set the face on carpet and carefully
and don’t put alott of pressure on the controls of the front panel. Remove

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of ef804s
tubes
Sent: Thursday, November 01, 2018 1:55 AM
To: [email protected]
Subject: Re: [TekScopes] 577 retrace problem

Hi Fred,

I glad you asked about this because at times I find this effect quite
annoying and at other times it seems like all the curve tracers I have owned
(2 x 575s, 1 x 576, 5 x 577s) have displayed it. By now these loops look so
familiar that I would have said your 577 (or 576, or 575) is behaving
perfectly normal.

In his original design for the 570 Vacuum Tube Curve Tracer, John Kobbe
rectified the power line to use for the plate sweep voltage. In the 575
Transistor Curve Tracer he used the same concept for the collector sweep
voltage. If you look at the waveform on the collector you would see a full
wave rectified sine wave.

I suspect your 577 isn't the problem at all. I think what you are seeing is
due to a combination of the transistor itself and to the way John Kobbe used
a rectified sine wave for the collector sweep. But there are actually two
plausible explanations:

1) My explanation is the transistor die is experiencing rapid heating and
cooling due to the collector voltage across it and the collector current
going through it. If this theory is correct then transistors with very small
die sizes would have larger loops due to the heating and cooling and
conversely power transistors with large die sizes and metal cases (like TO-
3) would have small loops or no loops at all. Also, if die heating is the
cause then the loop is going to be wider vertically at the peak of the
collector sine wave which is all the way at the right side of each step's
trace in the photo you took. But the loops ae larger on the left side of
your photo. So something is wrong with my theory.

Next I asked John Addis for his theory. Initially John also though die
heating was a possible cause. but after thinking about it he decided it
couldn't be die heating and he had a much better explanation which fits the
waveform you are seeing on your curve tracer. is what he thought at first:
Both heat (ΔVbe) and Ccb cause effects in this direction, assuming that the
upper part of each trace (above the loop) is associated with the decreasing
part of the rectified sine wave. However, the fact that it seems to be the
same magnitude at low and high Ib, argues for Ccb getting into the base
current.

2) John's final conclusion is as follows: The fact that this separation of
traces happens mostly at the part of the collector sine wave with the most
rapid change of voltage (not at top of the collector sine wave which
corresponds to the right most point on each trace) pretty well clinches the
Ccb explanation.

John Kobbe's original concept of using the rectified sine wave from the
power line became the collector sweep. Where the sine wave is rising from
zero toward its maximum, the rate of change in the collector voltage ΔV/Δt
is the greatest. This changing voltage results generates a current flowing
from the collector to the base through the Collector to Base capacitance,
Ccb. This Ccb current adds to the base current from the step generator
causing the trace to increase a small amount (move up on the CRT) creating
the upper part of the loop in each trace (compared to a capacitance-less
transistor). Once the rectified collector sine wave voltage passes its peak
and is coming back down to zero the effect is reversed and the Collector to
Base capacitance results in a small opposite current going into the base
which subtracts from the base step resulting in the lower part of the loop
in each trace. Since the collector voltage is the same for each base step
each loop is the same whether they are the lowest trace or the highest trace
on the CRT. To confirm Ccb causes the loops place two transistors on your
curve tracer. The transistor with the smallest Ccb will have the smallest
loop.

Another way to prove this to yourself is to put any transistor on your curve
tracer. Start on the 6.5V Peak Volts setting and a very large base step. The
effects of the collector voltage generating a noticeable current in your
base due to Ccb will be minimal resulting in no loops at all. Now switch to
the highest peak voltage the transistor can handle and notice that as you
decrease the base steps, and increase the vertical sensitivity to
compensate, the loops grow larger.

What John is saying is that Ccb, the capacitance between the collector and
the base, causes current to flow into the base causing the loops, and not
die heating. In addition to Ccb, the collector sweep voltage and the base
step size also contribute to the loops. If the 575, 576, and 577 curve
tracers used a sawtooth collector sweep you would not see this looping.

Dennis Tillman W7PF

The way to test this is to wire up a cascode arrangement of two transistors,
and curve trace that.
Since the whole rationale of a cascode is to mitigate the effects of Ccb,
the looping should disappear.

Craig




Dennis and Craig,

thank you so much much for the very informative answers. I used a TO3 BUX48A
for my tests. The comparators at the AC collector voltage provide a pulse at
90 degrees. You think it would be possible to feed this in a flipflop and
blank the trace from 90 to 180 degrees?

Best regards,
Fred