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I was talking about "aligning" audio circuits, e.g. adjusting operating
points of various stages, checking response, etc. Not about any sort of
RF work.

If I wanted to see a nonlinearity of a stage in an audio power amp, for
example, it'd be nice to believe that the scope's vertical system is
linear enough, etc. Same goes for step response: hard to do with a scope
that may well distort even a perfect square wave.

Anyone who is at all capable of making those kind of measurements
would surely measure the input square wave first. If it looks like
a square wave, then the scope is good enough for the task.

The input will look like a square wave even with a badly nonlinear vertical
channel. The output "square" wave will then typically be much slower than the
input one you fed to your system. With nonlinear vertical, the slower
transitions on the output square wave will look distorted, and you may end up
chasing ghosts, especially if the audio amp alignment procedure mentions
e.g. "adjust Rxxx for output transitions to be smooth".

I just don't believe in using unchecked instruments, and a reasonable way to
check a 7603 with plugins is to use the classic calibration trio in a TM503,
plus a mainframe standardizer.

How on earth can anyone recommend using an unchecked, unknown scope to a newb
is beyond me. Newbs tend to misunderstand limitations of instruments they
use, so they are very likely to just blindly trust the trace, even if someone
experienced would check things twice first. You know, things like using too
much or too little of vertical deflection, not centering the signal and
hunting differing rising/falling edge aberrations, and so on. It's just very
easy to hit those on an uncalibrated scope methinks.

Cheers, Kuba

Kuba Ober wrote:

Given that IIRC the OP doesn't have a spectrum analyzer, you'll want to
get
step or pulse responses of the audio gear you're testing. I can hardly
see
that going all too well with an uncalibrated scope.

Audio "alignment" is essentially calibration work, and I can't see doing
that
with a scope that I know nothing about.

Have you ever ACTUALLY aligned a receiver?

I was talking about "aligning" audio circuits, e.g. adjusting operating points of various stages, checking response, etc. Not about any sort of RF work.
If I wanted to see a nonlinearity of a stage in an audio power amp, for example, it'd be nice to believe that the scope's vertical system is linear enough, etc. Same goes for step response: hard to do with a scope that may well distort even a perfect square wave.

Gee Kuba,

Anyone who is at all capable of making those kind of measurements
would surely measure the input square wave first. If it looks like
a square wave, then the scope is good enough for the task.

-Chuck Harris

On Wednesday 07 February 2007 13:56, you wrote:

Kuba Ober wrote:

Kuba wrote:

Well, if all you care about is *basically working*, then I agree. But
then you don't need a 7603 either. A random 7603 with random plugins will
*basically* work, but most of the time it doesn't really perform as a
dependable 100MHz instrument. Maybe it's my luck, but 90% of the plugins
that I bought in lots on eBay showed signs of being seriously
miscalibrated, and two of my mainframes (7603 and a 7633) were quite
miscalibrated as well; their pulse response was completely off limits and
you need the standardizer for that.

Cheers, Kuba

Kuba,

The origin of many instruments on eBay are government surplus, or surplus
acquired by someone with no calibration skills. In the first case,
metrology (instrument calibration) technicians in gub ment would screw up
an instrument they are trying to dump (or are instructed to do so) so it
gets tagged "unusable". The other case results from uneducated people
trying to fix something that ain't broke.

True, but given such a miscalibrated state, would you trust the instrument for
anything serious?

I guess for basic RF stage alignment you don't even need a scope, an RF RMS
voltmeter with a phase detector/indicator would probably suffice. I used such
a phase-indicating RF voltmeter back in high school to fix an ailing RC
receiver. It had a single mixer, an IF filter & amp, and it'd directly
demodulate the RF, if I remember things right. Due to vibration or whatnot
the two little coupling transformers had the slugs at all the wrong places,
and there was also a little air-wound coil with a couple turns that somehow
got distorted (maybe someone played with it too much) and needed bringing
back to shape. Being a total RF newb it took me a couple afternoons to figure
it out, but in the end I had it working. I had a scope, but all I cared for
was to get the response peak in the right place, and the voltmeter did just
that, and the scope's probe seemed to load the circuit too much. The
voltmeter had a couple different probes, two non-contact ones, and three
contact ones. I don't remember their specs, though. You needed one probe for
the voltmeter, and optionally another one for phase reference.

For non-RF-alignment work, e.g. audio amplifier design/testing/adjustment, you
will need to look at time-domain response, and for that you better had a
scope that's linear in both X and Y subsystems. How can one just assume that
it's the case with an unknown scope and not much to test it against??

Cheers, Kuba

Given that IIRC the OP doesn't have a spectrum analyzer, you'll want to
get
step or pulse responses of the audio gear you're testing. I can hardly
see
that going all too well with an uncalibrated scope.

Audio "alignment" is essentially calibration work, and I can't see doing
that
with a scope that I know nothing about.

Have you ever ACTUALLY aligned a receiver?

I was talking about "aligning" audio circuits, e.g. adjusting operating points
of various stages, checking response, etc. Not about any sort of RF work.

If I wanted to see a nonlinearity of a stage in an audio power amp, for
example, it'd be nice to believe that the scope's vertical system is linear
enough, etc. Same goes for step response: hard to do with a scope that may
well distort even a perfect square wave.

Cheers, Kuba

From: Kuba Ober

The original question was about a scope for audio and tuner alignment.

Given that IIRC the OP doesn't have a spectrum analyzer, you'll want to
get
step or pulse responses of the audio gear you're testing. I can hardly
see
that going all too well with an uncalibrated scope.

Audio "alignment" is essentially calibration work, and I can't see doing
that
with a scope that I know nothing about.

Cheers, Kuba



Have you ever ACTUALLY aligned a receiver? The most primitive scope
suffices. A 503 is overkill. Suggesting that it's akin to calibration is
audiophoolery. I guess you'd say you need a TDR to check your speaker
wires too.

All you have to do is get the IFs properly tuned (think diode probe flat
from 10.6 to 10.8 MHz) and get the RF stage (if any) to track the
oscillator properly. The trickiest part is the stereo circuitry and that
requires a special generator. A decent generator is FAR more important
than the scope.

-John

Kuba Ober wrote:

Kuba wrote:

Well, if all you care about is *basically working*, then I agree. But then you don't need a 7603 either. A random 7603 with random plugins will *basically* work, but most of the time it doesn't really perform as a dependable 100MHz instrument. Maybe it's my luck, but 90% of the plugins that I bought in lots on eBay showed signs of being seriously miscalibrated, and two of my mainframes (7603 and a 7633) were quite miscalibrated as well; their pulse response was completely off limits and you need the standardizer for that.

Cheers, Kuba

Kuba,

The origin of many instruments on eBay are government surplus, or surplus acquired by someone with no calibration skills. In the first case, metrology (instrument calibration) technicians in gub ment would screw up an instrument they are trying to dump (or are instructed to do so) so it gets tagged "unusable". The other case results from uneducated people trying to fix something that ain't broke.

Bill Roberts

A newbie may well not discern when someone is kidding and when not, and
may be too shy or something to ask for clarification. I prefer to be
straight forward than send someone off on a wild goose chase. YMMV.

I'd rather think that advising a newbie to buy an uncalibrated, unknown 7603
is sending him/her on a wild goose chase. A newbie will not have enough
experience to easily ascertain whether something is a scope issue or the DUT
issue.

Heck, I'd be uncomfortable using an off-eBay 7603 where all there is to test
it out is a 1kHz calibrator square wave.

Said newbie would do well to get some equipment to at least partially check
out the 7603, which really means a TM503 loaded with the amplitude
calibrator, time mark calibrator, and the levelled sine wave generator. Plus
requisite plumbing and attenuators. That's really the most basic setup. And
will cost approx. $500, depending on luck. The $1000 was a rough order of
magnitude.

Cheers, Kuba

The original question was about a scope for audio and tuner alignment.

Given that IIRC the OP doesn't have a spectrum analyzer, you'll want to get
step or pulse responses of the audio gear you're testing. I can hardly see
that going all too well with an uncalibrated scope.

Audio "alignment" is essentially calibration work, and I can't see doing that
with a scope that I know nothing about.

Cheers, Kuba

I would recommend the 7603 with a 7B53 Time Base and a couple of 7A18
Vertical Amps. You can get that combo for $125 or less. With the plethora
of other plug-ins available you would have a versatile system that is
easily repairable

Assuming you have approx. $1000 worth of other test equipment needed to
recalibrate said 7603 :)

It's an easily snowballing hobby.

NONSENSE: You can easily verify that a 7603 is basically working using
it's internal calibrator. and a length of wire For most work....
including the genesis of this thread... you don't need a lab quality
calibration. In fact, a 60 year old AC coupled DuMont would work just
fine.

Well, if all you care about is *basically working*, then I agree. But then you
don't need a 7603 either. A random 7603 with random plugins will *basically*
work, but most of the time it doesn't really perform as a dependable 100MHz
instrument. Maybe it's my luck, but 90% of the plugins that I bought in lots
on eBay showed signs of being seriously miscalibrated, and two of my
mainframes (7603 and a 7633) were quite miscalibrated as well; their pulse
response was completely off limits and you need the standardizer for that.

Cheers, Kuba

On Monday 05 February 2007 23:41, you wrote:

Beside collecting TM500 plugins, anyone actually usem, in particulars,
the AM501. Just got two of em.

I'd like to use a FG504 & FG501A plus other signal generators to
create all different types of waveforms. Integrating,
differentiating, ...

Any suggestions? Any neat experiements?

Specificatioins of the AM501? Comparisons with modern OP-Amps?

Anything that has got banana jacks on it *may* perform poorly for anything
above a few kilohertz due to parasitics, unless you put the feedback path next
to the chip. It does have a place to solder components inside, BTW. The
op-amp inside of AM501 can be replaced by a more modern chip, if you wish so.

The plugin itself was designed for teaching op-amps, and has little utility
beyond that methinks.

For source of great op-amp circuits, download this *excellent* book:

Applications Manual for Computing Amplifiers for Modeling, Measuring,
Manipulating & Much Else.


Then you'll want to get Troubleshooting Analog Circuits by Bob Pease, which
has an excellent section on real life op-amp behavior.

All in all, a good source of experimentation data is
, which has tons of analog computation
applications etc.

Cheers, Kuba

Hello Chris,
On A41 there is a chain from GND to +50V: R177 (35k7) - R176 (2k
trim, Shield Voltage) - R175 (12k7). The slide of R176 is decoupled
by C175 (0.01uF) to ground. Location R176 is what you said.
Calibration 9A Adjust Shield Volts:
a) Short vert.defl. leads together
b) DC meausure voltage on defl. leads.
c) remove short
d) DC measure pin 4 of P41U on the Z-axis board
e) Adjust R176 for approx. same reading as in b)
Success.
Albert

--- In TekScopes@..., "Christopher Hilton-Johnson"
<chj@...> wrote:

Greetings etc



I have a late model 7704A & an earlier manual. BAMA is no help.

Z axis board is suffix 01, my manual is for suffix 00.

Suffix 01 board shows an additional trim pot immediately below

R171, the Geometry trimmer.

Additional trim pot obscures the screen printed board ID, but I

think it is a variable version of R175 fixed @ 2k2 on the suffix 00
board.

Naturally my manual is silent on incorporating this variable into

the calibration process.

Can anyone help please?



Chris HJ


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Chris Johnson wrote:

Personally, I've always thought that the graticule should be an
overlay that's application specific and the CRT face is always clear,
so one tube type can be used in many products. But Tektronix tends
to go for the optimal solution for a given product rather than one
that's a little bit of a compromise. The integral graticule IS better.

If you go with an external graticule, the marking will be at least 1/4 inch
away from the phosphor. That leads to a rather nasty parallax problem.
Internal, or electronically drawn graticules are really the only way to go.

-Chuck

A lot of Tek CRTs are different only in how the graticule is marked.

For example, if it weren't for the fact that the graticules are
different, I could swap the pristine, very low hours CRT from my OF150
optical TDR into my 492 if I needed to. Fortunately, the 492's CRT
is in excellent shape. And I COULD do the swap, but the OF150's
graticule is graduated to 8 divisions by 8 divisions and the 492's
graticule is graduated in a 10 by 10 division pattern, and the
reference markers are different. It would be either very confusing
or you'd have to totally change the calibration of the analyzer if you
were to use the OF150's tube...if you wanted to be able to rely on the
graticule for any information, that is.


Personally, I've always thought that the graticule should be an
overlay that's application specific and the CRT face is always clear,
so one tube type can be used in many products. But Tektronix tends
to go for the optimal solution for a given product rather than one
that's a little bit of a compromise. The integral graticule IS better.



--- In TekScopes@..., <bhaskins@...> wrote:

I have often wondered about the actual differences in Tektronix CRTs.
Within a basic class the tubes appear to be identical except for the

part number.

Please cut me lots of slack on the word appear.
Just for example take the 465/a/b/m, 2213/3a/15/15a,and many others.
Quite some time ago, I got a nice 465B for almost nothing and it had

a dead crt.

I had almost nothing to lose so I tried a jug from a 465M which had

a badly

broken case.
It has been running fine for about four years now.
Any thoughts?

I'd agree with this. I used to have a 465M and it was a pretty good
scope. You can get them dirt cheap on Ebay. For the original
poster, if you're comfortable designing, building, and debugging
audio stuff, you shouldn't have much trouble fixing any issues on a
465M. The horizontal and vertical sections are easily removed
(unlike the other 460-series scopes). The only problem mine had,
which I've seen other people post similar symptoms for, was the
sweep trace was horizontally compressed. The problem was with a
capacitor in the power supply causing one of the DC supply rails to
be both too low, and not DC.

Dan

--- In TekScopes@..., <bhaskins@...> wrote:

For a real bargain look at a 465M, much better that either of
those two, I've owned both, and much more portable than
the 76 series.
The 465M is a real sleeper... a great scope except when you want
to sell one.
I like my 7623a very much except when I need to carry it
somewhere.

This is my first post to this group. I build DIY audio for

myself and

the more I read/talk to individuals it seems like an Oscope

should

definitely be on my list of things to purchase. Honestly, I

can't tell

you why I would need a 4-channel vs. a 2-channel scope other

than 4 is

greater than 2. But I would be interested in your comments. I

am

interested in the 2465B but it seems like prices range from

$150 -

$1200. If someone can point me in the right direction, I would

really

appreciate it. BTW, I'm guessing that all of you would

recommend that

buying an Oscope from eBay (as my first Oscope) would not be
recommended. :) Please let me know if you disagree. Also, my

budget

is between $200-$300.

Oh no... it just so happens my wife and I are traveling to
Vancouver next week, but I'm sure she would not be interested in
taking a day from our vacation to drive to Kelowna to pick up old
electronics parts! :-)

Maybe some people in the Seattle area will be interested in driving
up there.

--- In TekScopes@..., "wshawlee2" <walter2@...> wrote:

I don't have time or desire to pack and ship it, but for anybody
thinking of trip up this way to beautiful BC (Kelowna), let me

know,

and I will start a pile for you. contact me off list for more
details. even with thousands of feet of space, and two storage
buildings, we are just out of space, so some stuff has to die.

This is

the moment.

Hello:
I need to verify the wiring to the fan on the Tek 453 which I just
acquired as first scope. Works fine, but fan bearings were dry. Got it
going but cannot verify with certainty the solder points for the green
and black fan leads. There is a broken solder point at the forward most
of two contacts just to the left as viewed from the front. Behind this
is another contact where blue and blue/white are soldered.

I am assuming (no manuals yet) that green and black leads broke off
from the front most contact. Naturally, I would like to verify this
before re-soldering.

Any help is greatly appreciated.

John

I tried that today and it works quite well once you know what to do.

Connect vertical output to line level input of a regular stereo
receiver or amplifier, plug in the headphones.
Digital storage OFF. Get in close to the signal of interest, changing
spans as you get closer, switch to manual sweep, and at suitably high
resolution modes, tune in on the signal. Going to manual sweep
makes this fast and easy, and you don't even have to go to zero span,
but of course, going to zero span and entering oscilloscope mode can
assist you to get optimized signal quality, not clipping on either
the top or the bottom of the waveform.

I went signal hunting in several ranges and started with the local FM
radio stations for a wideband signal introduction, then went to the
VHF weather radio station at 162.55 MHz, then went into the aircraft
band (108-136 MHz) to try to track down some aircraft transmissions
with limited success, and then went down to the AM radio band, and
then found some amateur radio traffic around 14.3 MHz, voice and CW
both. And a few assorted international stations in various parts of
the HF bands, too. Switching the bandwidth filters allowed me to
get good recovered audio quality on every signal I tuned in. Having
very good headphones and a nice amp certainly didn't hurt.


I'd guess there are some limitations on what you can get out of the
video output. I can't imagine that it really has the bandwidth
necessary in order to, for example, be usable as a video source
with an external output. (Say I tuned in a TV station at the
appropriate bandwidth setting.)


CJ





--- In TekScopes@..., "Stan and Patricia Griffiths"
<w7ni@...> wrote:

Hi Chris,



I used to demo the 492 as a "receiver that looks like a scope".

This made

it much easier for the average person who was not familiar with spectrum
analyzers to quickly grasp how it worked. I used the video output

to drive

a Radio Shack telephone amplifier by plugging the video out directly

into

the suction cup microphone input on the amp and I think the levels

are just

fine. The Radio Shack telephone amp is powered by a 9 volt battery

so it is

portable and cheap. Use zero span and slope detection for FM

signals and

peak detection for AM signals. At shows where I was exhibiting more

than

one spectrum analyzer, the 492 provided the audio for a TV signal

and the

2710 provided the video. For those of you who may not know, you can
actually get a TV picture to display on the screen of a 2710 spectrum
analyzer. The biggest complaint about this was that it was not in

"color".

My response was that "green is a color".



Stan

Aaaah.... empirical design. This always works.

On Tue, 06 Feb 2007 19:33:21 +0100, J Forster <jfor@...> wrote:

My reading was the guy was looking for a first scope for audio. I think
it would be an error to get a 7A22 instead of a 7A18 or 7A26.

Maybe if it was a "instead" question it would be an error, but luckily it is only "what first", standard PIs are cheap.

I would expect the MF will come with some useful plugins (or it may not if it is a bargain, i recently saw a 7603 with a logic analyzer inside go for coins, in the US). The rest of the PIs will have to be bought as needed.

If it was a normal scope, you'd be stuck with the simple inputs you got. Let's go and worship our 7k scopes a little, they deserve it. Maybe another capacitor offering is due ;-)

ST

Greetings etc



I have a late model 7704A & an earlier manual. BAMA is no help.

Z axis board is suffix 01, my manual is for suffix 00.

Suffix 01 board shows an additional trim pot immediately below R171, the Geometry trimmer.

Additional trim pot obscures the screen printed board ID, but I think it is a variable version of R175 fixed @ 2k2 on the suffix 00 board.



Naturally my manual is silent on incorporating this variable into the calibration process.



Can anyone help please?



Chris HJ


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