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Well I guess you get what you pay for. At $50 for a 2440 should have been
a clue. So far the first 2440 I turned on has cal errors
4000 FPP fail
7000 CCD fail
8000 PA fail
all others passed

Maybe I should go through an external calibrate first?
Bob

Hello,

I'm interested in purchasing my first scope and looking for opinions on the
TDS744A. I'm not interested in purchasing a Rigol/Siglent, etc - not that
they are bad scopes, I've used Teks before at different employers. It's
just that I'm not familiar with this particular model. It'll be used for
working on amateur radio related radios, experimentation and general
messing around :) I know it can be modified to a 1GHz scope and might do
that in the future.

Thanks for reading.

73! Mark KA6WKE

Website:
Author: 4NEC2 The Definitive Guide EMail List:: [email protected]

Did the TEK factory have the fan suck air in or blow it out the back?
kevin

Hello,

I'm interested in purchasing my first scope and looking for opinions on the
TDS744A. I'm not interested in purchasing a Rigol/Siglent, etc - not that
they are bad scopes, I've used Teks before at different employers. It's
just that I'm not familiar with this particular model. It'll be used for
working on amateur radio related radios, experimentation and general
messing around :) I know it can be modified to a 1GHz scope and might do
that in the future.

Thanks for reading.

73! Mark KA6WKE

Website:
Author: 4NEC2 The Definitive Guide EMail List:: [email protected]



.

Chuck,

He would change them 3 or 4 at a time. Now we see two or three over 5 or 6 units.? The 6130C uses 22 (or so) and the OEM HP ones were unstable.? HP got better, but at the time (1979) they broke at the drop of a hat.

Other folks, Monsanto, LiteOn, etc, all seemed more stable and reliable.

steve

I would like to hear from others what they do to make the 7S11/7T11
sampling plugins easier and more reliable to use.

The DPO used a DEC PDP-8 minicomputer to capture data from the 7704
lower section plugins and display the results on the 7704 upper
display section. Tek listed the DPO in its catalogs from 1974 to 1981.
In 1981 Tek introduced the
7854 which does all of this in a normal size 4-wide mainframe using a
microcomputer instead of the PDP-8 minicomputer.

Hi Michael.
I changed the subject since it has been about the 500 series SCOPES
and not CURVE TRACERS until now.
In the next few days there will probably be many replies to this question.
I request that everyone keep the discussion dignified.

For 99% of our members the most important consideration will be which
one you can get at an affordable price. They are both wonderful
instruments especially if you have nothing else.

Since you are in the 1% category that owns both a 576 and a 577 (and
so do
I) 1 I will comment on which one meets my needs and why.

The first thing I think of, that I believe Deane also thought was
important, was the storage capability of the 577-D1. It has a drawback
as well - it can be annoying when it is not adjusted properly. I have
followed the internal adjustment procedure carefully for adjusting the
storage voltages with little success so I live with the occasional
storage artifacts. Another reason I like the 577 is because I am also
interested in testing the additional things my 178 "front porch" can
test (OpAmps, Voltage Regulators, SCRs, etc).

I personally think the 576 is the most beautiful instrument with a CRT
that Tek ever made (In that respect I'm a romantic). Many 576 owners
love the readout which helps to avoid mistakes when measuring
parameters. This is not something I need. Like my annoying storage,
the fiber optic readouts have their own issues. Most 576s have some
dark fibers by now and there are no replacement readouts that I know
of. I don't think there is a practical way to repair individual fibers
either. The 576 has its own specialized "front porch", the 176, for
testing power transistors which is important for some users. The 576
was incredibly expensive to build and Tek did not make much, if any, profit on each they sold.

The 577 was designed to fix that problem. Tek engineers borrowed
heavily where they could to keep costs down. For example, the entire
display section was borrowed from the 5000 series of scopes. My
principal complaint about the 577 is due directly to this lineage:
there is no Graticule Illumination. That is problematic when I want to
take a photo of the curves on the screen and the graticule lines do
not show up in the photo so it is almost impossible to know what the V
& I of each curve is. Instead I discovered an alternative way to add a
graticule overlay after I take the photo of the semiconductor
characteristic curves. But this is still an annoying oversight from
Tek. One final thing in the 577's favor: it was released several years
after the 576 and in the intervening years several new types of
semiconductor devices were developed and the design team made sure the 577 could test those devices.

You are probably wondering why I find the storage of the 577-D1 to be
essential. Here are four examples:
1) Junction (bipolar) FETs are notoriously temperature sensitive in a
curious way. Below a certain bias point the temperature coefficient is
negative, above this bias point the temp coefficient is positive. So
display a FET on a non-storage 577-D2, pick some typical gate bias
voltage steps, and look at the curves you get. You can't tell where
the gate bias point is exactly at the midpoint between the positive
and negative temp coefficients. If you do the same thing with the
577-D1 and turn the storage on all you have to do is change the
temperature of the FET by applying a little heat to the FET and the
curves above the critical bias point will move up and curves below
this point will move down. The storage displays the bias point where
nothing moved and that is the critical zero Temp coefficient bias point you should design for.

2) With storage turned on put a transistor in the left socket and
another one in the right socket and toggle left to right and you can
immediately tell if they match and by how much. The curves won't
overlap unless they are matched.

3) This is a little trickier but I have used storage to find two power
transistors (one NPN and one PNP) that had Beta close enough to make a
near perfect class B output stage. I had the NPN in the left socket
and I displayed the curves for it in the upper right quadrant of the
577-D1. Zero collector voltage and current was located at the exact
center of the screen. Then I stored the top half of the screen. Next I
did a similar thing with the PNP which was in the right socket. Again
zero voltage and current were set to the center of the screen and its
curves were positioned into the lower left quadrant. Then I stored the bottom half of the screen.
There was a perfectly linear load line from the negative PNP collector
voltages and currents on the bottom left of the screen to the positive
NPN collector voltages and currents in the upper right part of the screen.

4) At extremely low collector currents Miller capacitance, socket
capacitance, transistor noise, and AC (hum) pickup distort each
collector V vs. I curve into a noisy loop. As you switch to more
sensitive ranges the loops occupy a larger portion of each step until
the steps themselves are totally obscured by the capacitance,
transistor noise, and AC pickup. The solution is to switch to manual
+DC or -DC and use the display filter to reduce the noise. With
storage you can vary the collector voltage manually and trace out the
entire set of characteristic curves just fine on the CRT no matter how
sensitive the range you select. With a 576 or a 577-D2 you would have
to use a grease pencil to mark your progress on the CRT to see the curves.

Dennis Tillman W7PF

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Mlynch001
Sent: Wednesday, August 14, 2019 7:10 PM
To: [email protected]
Subject: Re: [TekScopes] 5xx 'Scopes

On Wed, Aug 14, 2019 at 01:24 PM,

I once asked Deane Kidd, when I was in his lab, which he
recommended,
576 or 577. His answer was definitive: the 577 hands down. So that
is what I found to replace my 575 10 years ago. I have had both the
577-D2 and 577-D1 over the years since and there is no question that
the 577-D1 (storage) version has more capabilities although the
storage is tricky to adjust and is sometimes annoying.

I am now fortunate to own both a 576 and a 577 and all the optional
"front porches" so I can test just about anything. . .

Dennis Tillman W7PF

Dennis,

Is there as specific reason that the 577 is the preferred instrument?
I have both working instruments and am looking to sell one of the two.
I do not know enough about either to say which is better. Looking for
some sage advice.

Thanks

Michael Lynch
Dardanelle, AR




--
Dennis Tillman W7PF
TekScopes Moderator