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Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Chuck Harris
 

Another way, possibly, is to scan through the catalogs
from about 1978 through 1981.

I looked in my 1981 catalog, and I find that I am misremembering
a lot of things about the 7L13 and 12.

-Chuck Harris

Attilio wrote:

You're right Chuck, I think it's great from 1 MHz and that at very high frequencies there is the problem of not being able to see the harmonics.
But I fell in love with the 7L13 and will use it in HF, VHF and UHF where I think it gives its best.

I took off the TUNING knob and noticed that it is heavy so it acts like a flywheel when tuning.
I think the only way to find out the truth is to ask someone who worked at Tektronix and knows the whole story of 7L13.

Thanks a lot Chuck.
Greetings
Attilio
Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

 

You're right Chuck, I think it's great from 1 MHz and that at very high frequencies there is the problem of not being able to see the harmonics.
But I fell in love with the 7L13 and will use it in HF, VHF and UHF where I think it gives its best.

I took off the TUNING knob and noticed that it is heavy so it acts like a flywheel when tuning.
I think the only way to find out the truth is to ask someone who worked at Tektronix and knows the whole story of 7L13.

Thanks a lot Chuck.
Greetings
Attilio
Re: Asking for Help with Verifying Genuineness of 2465B from Ebay

 

Chuck et al,

Perhaps this list of what's what in various models (2445, 2445A, 2445B, 2465, 2465A, and 2465B) could be made into a document stored here in groups.io and in the tekwiki. It would have textual descriptions of the salient differences, a set of pictures of the parts that vary so that identifying what is in front of you on the bench becomes a 'look and match' experience. This issue of scopes sold as things they are not has been raised before and will no doubt be again. Maybe a google docs shared spreadsheet would be a suitable starting point?

Cheers, Brian.
Re: Tek 465 S/N B299598 Slight Horizontal trace jitter

 

Do you see the jitter even without a signal input? Does it vary when changing the position of the volts/div switch? Before you do anything else, check for loose connections/poor solder points in the vertical input area.
Re: Tektronix 317

 

I, too, have one.? Mine's marked @T-1 309 just under the edge of the
battery holder. G-1432-XA under it.
I bought it for my 2440, the scope on the cover of the manual.

On 12/22/20 8:52 PM, Larry McDavid wrote:
I have one of these Scope Evaluation Boards. Mine is marked, "T-1419,"
not T-1449; maybe just a typo.

Yes, one side is essentially 90% 9-volt battery holder.

I did not have the extensive instruction manual, however. Thanks for
that, Bob.

Larry


On 12/22/2020 12:38 PM, Bob Albert via groups.io wrote:
? It's called a scope evaluation board and is about 30 years old.?
Most of it is a battery holder.? There is a number T-1449 on it and
has 3 ICs.
Bob
???? On Tuesday, December 22, 2020, 12:21:48 PM PST,
<brockkoren@...> wrote:
? ? oh they won't allow that email, maybe bkoren@...
--
Jeff Woolsey {{woolsey,jlw}@jlw,first.last@{gmail,jlw}}.com
Nature abhors straight antennas, clean lenses, and empty storage.
"Delete! Delete! OK!" -Dr. Bronner on disk space management
Card-sorting, Joel. -Crow on solitaire
Re: Tektronix 317

 

I have one of these Scope Evaluation Boards. Mine is marked, "T-1419," not T-1449; maybe just a typo.

Yes, one side is essentially 90% 9-volt battery holder.

I did not have the extensive instruction manual, however. Thanks for that, Bob.

Larry

On 12/22/2020 12:38 PM, Bob Albert via groups.io wrote:
It's called a scope evaluation board and is about 30 years old.? Most of it is a battery holder.? There is a number T-1449 on it and has 3 ICs.
Bob
On Tuesday, December 22, 2020, 12:21:48 PM PST, <brockkoren@...> wrote:
oh they won't allow that email, maybe bkoren@...
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
Re: Tek 465 S/N B299598 Slight Horizontal trace jitter

 

To clarify, when you say "jitter" I'm concluding that you mean the entire trace is randomly jumping in the vertical only? Your signal is triggering and the horizontal sweep is stable?

Dave,
Thank you for your interest.
The jitter is very small and and yes it is the entire trace but specific to CH1 only. It isn't showing up in area as I went thru testing that Jeff Dutky suggested. As I had assumed that I would find it there. The position control is smooth and there really isn't any dead spots or indication of excessively dirt pot. I haven't started down the calibration path yet as was just evaluating conditions of the scope. The signal I am applying a 1Khz 300mV signal. But can change it to a DC voltage signal as advised. I have removed cleaned and reseated the majority of the transistors if they were accessible without removing and boards. I will get back with you as I go set by step thru your questions.

Craig
Re: Asking for Help with Verifying Genuineness of 2465B from Ebay

 

Thanks for that¡ªthe second reference has exactly the error that I was recalling. The implication that a single-pole system has a Gaussian response is one of the rare mistakes Tek allowed in print.

Cheers
Tom

Sent from my iThing, so please forgive brevity and typos

On Dec 22, 2020, at 20:11, Mr. Eric <engr.eric@...> wrote:

Tom,

I loved the idea, I hadn't thought about leaving it calibrated although that's what I would have done on my DSO or what I would have done even just a year ago on an analog scope. Unfortunately I tried it and the result was exactly the same, 1.09ns. So I realize that this BW approximation technique is not the end all be all. But it is a very interesting experiment in and of itself that allows me to learn a lot more. So in that aspect, I think it's absolutely awesome. So I can't thank everyone enough for their help, ideas, and knowledge!!!! I'm a Computer Engineer by trade and degree, which means my skill lies somewhere between a bad EE and a bad Software Developer. But these are all the little aspects that contribute to my growth =)
Re: Asking for Help with Verifying Genuineness of 2465B from Ebay

Mr. Eric
 

Tom,

I loved the idea, I hadn't thought about leaving it calibrated although that's what I would have done on my DSO or what I would have done even just a year ago on an analog scope. Unfortunately I tried it and the result was exactly the same, 1.09ns. So I realize that this BW approximation technique is not the end all be all. But it is a very interesting experiment in and of itself that allows me to learn a lot more. So in that aspect, I think it's absolutely awesome. So I can't thank everyone enough for their help, ideas, and knowledge!!!! I'm a Computer Engineer by trade and degree, which means my skill lies somewhere between a bad EE and a bad Software Developer. But these are all the little aspects that contribute to my growth =)
Re: Tek 465 S/N B299598 Slight Horizontal trace jitter

 

On Tue, Dec 22, 2020 at 07:03 PM, Jeff Dutky wrote:


If you are only seeing the jitter on one channel then it MUST be in the
pre-amps before the channel switch.
Jeff Dutky,
Thank you for your intrest.
Went thru the readings as you described ahead of vertical switching TP364, TP374 and after vertical switching TP322, TP324 and made comparisons, I see no jitter in these area's and the signals look very comparable. Used both a digital and analog scope to check and compare the test points It seems to be more prominent during a cold startup. So I will measure these points during a cold start as the instrument is well warmed up now.

Craig
Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Chuck Harris
 

Hi Attilio,

It has been about 15 years since I sold my 7L5, 13, and 18,
and bought an HP 8566B. I liked the 7L stuff, but the HP is
orders of magnitude better to work with.

The original knob had a clutch in it, and was used to fine
tune the analyzer when the unit was in the narrow bandwidth
phase locked settings with narrow filters. I think the 7L12
left off the narrow filters, and the phase lock hardware, and
maybe yours had that done as well?

Close to the bottom of the band, the LO is almost at the IF
frequency, and swamps anything that comes in the RF port.

LO - IF = RF, so at 1KHz, the LO is 1KHz above the IF frequency.

You really shouldn't expect much from a 7L13 at the lowest
frequencies. It is more a 1MHz to 1.8GHz analyzer. It does
a nice job characterizing HF, VHF, and UHF signal sources.

Similarly, you can't tell much about a very high frequency
source, as any harmonic content will be out of the range of
the analyzer.

-Chuck Harris

Attilio wrote:

Thank you very much Chuck, I will not make the change to bring it to 2.5 GHz, instead I wanted to ask you what is the real analysable minimum frequency, I have seen that approaching 1 kHz it becomes difficult to visualize the signal due to the proximity of the internal local oscillator carrier .

As for the Tuning control, I assure you that everything looks original and on the front there is only the word TUNING and not PUSH / PULL.
I don't know what to say about it.

Greetings
Attilio
Re: Tek 465 S/N B299598 Slight Horizontal trace jitter

 

If you are only seeing the jitter on one channel then it MUST be in the pre-amps before the channel switch.

It looks like the 465 doesn't have an IC for channel switching (I'm only familiar with the 475 which has a channel switch IC): it looks like it's done by two pairs of diodes, CR305/CR307 (ch 1) and CR315/CR317 (ch 2). There are two test points that let you see the signals controlling those diodes (TP374 and TP364 for ch 1 and ch 2 respectively). You could see if the jitter is visible on TP374. If so, I guess that would implicate either the diode pair (305/307) or something around Q374.

-- Jeff Dutky
Re: Tek 465 S/N B299598 Slight Horizontal trace jitter

 

Hi Craig,
Have you stepped through the calibration procedure in the service manual? It would be good to be assured that all the preliminary settings and checks are clear. Like the 55v is driving the first stage bias. It'd be good to know it is good and stable.
To clarify, when you say "jitter" I'm concluding that you mean the entire trace is randomly jumping in the vertical only? Your signal is triggering and the horizontal sweep is stable? This sounds like vertical position pots that are "noisy". That is the vertical position does not move smoothly as the knob is turned through it's range. That is typically improved by repetitive turning of the knob and use. Does the "jitter" respond to touching or moving of the position knob?
Your R25 issue does seem to indicate a CH1 pre-amp bias issue. I would not conclude right away that there's a problem with R25 itself. I would be curious to know how calibration has gone with position centering (R115) and Var Balance (R120). I'm wondering if there's an issue with the position pot itself (R302). Might explain both conditions. I'm a bit surprised you don't see noise on CH1 test points, and that they are matching CH2.
You're applying a square wave to both CH1 and CH2. What is it's frequency, hi and lo values, and is this what you are measuring at the test points? Or a DC value? A DC value might simplify things, but the square wave is fine. You just have to measure both levels, and are you measuring differential or relative to ground? If you're having a bias issue measuring all four values relative to ground might be more revealing than differential values: CH1+ (TP141), CH1- (TP147), CH2+ (TP241), CH2- (TP247).
Portions of the pre-amp are current based signaling - you may not see a voltage noise at the above test points. I'm wondering if there could be issues with, for example, Q304/Q308. The transistors in these scopes are plug-in, and a little schmutz on the leads could cause noise. You might want to carefully identify, remove, and clean the leads on these. So many of these scopes have been idle in hardly ideal conditions. This would not be the first case of a problem caused by connectivity problems with plug-in parts. Corrosion happens.
I'm not an expert. Just beginning this journey myself. But these are the things I'd be looking at. When communicating debug info don't be shy to be very explicit and very thorough. It's hard to know what's going on when one doesn't have the circuit in front of them. A little too much info is better than a little too little. But you've got to start somewhere, and I understand not wanting to do a big data dump when you're just trying to feel out the feedback. Let me/us know how it goes.
Dave

On Tuesday, December 22, 2020, 06:00:49 PM PST, Craig Cramb <electronixtoolbox@...> wrote:

Dealing with a 465 scope that is having a condition on CH1 that the trace has a slight jitter to it. Less than .1 but it is annoying to me.? Is visible when a signal is displayed or when the Attenuator is in the GND position. CH2 trace is solid smooth in any condition no jitter at all. I have gone thru the A3? CH1 Vertical preamp suspecting the condition would be located there. But reading thru all the test points thru this circuit and comparing CH1 to CH2 test point values they are all the same. No indication thru this board of any slight jitter.
Any thoughts of where this might be coming from that there is a difference in the? CH1 and CH2 signal. I'm applying a common square wave to both inputs and selecting Chop mode then tracing thru the CH1,CH2 test points.

There is another issue, the balance on CH1 is not working as it should when trying to get Trace shift to less than .2V? I can get it real close in balance but then the position adjustment for the trace won't travel thru the entire graticule scale.? Which this might be the trim pot R25. But would like to pin down the other issue first before removing the preamp board to replace this resistor.

Any thoughts would be greatly appreciated.

Craig
Tek 465 S/N B299598 Slight Horizontal trace jitter

 

Dealing with a 465 scope that is having a condition on CH1 that the trace has a slight jitter to it. Less than .1 but it is annoying to me. Is visible when a signal is displayed or when the Attenuator is in the GND position. CH2 trace is solid smooth in any condition no jitter at all. I have gone thru the A3 CH1 Vertical preamp suspecting the condition would be located there. But reading thru all the test points thru this circuit and comparing CH1 to CH2 test point values they are all the same. No indication thru this board of any slight jitter.
Any thoughts of where this might be coming from that there is a difference in the CH1 and CH2 signal. I'm applying a common square wave to both inputs and selecting Chop mode then tracing thru the CH1,CH2 test points.

There is another issue, the balance on CH1 is not working as it should when trying to get Trace shift to less than .2V I can get it real close in balance but then the position adjustment for the trace won't travel thru the entire graticule scale. Which this might be the trim pot R25. But would like to pin down the other issue first before removing the preamp board to replace this resistor.

Any thoughts would be greatly appreciated.

Craig
Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

 

Wow, okay. That doesn't sound like a HARD failure (no smoke), and the LOW LINE indicator is, to my mind, a very suggestive symptom. My limited experience with the power supply on the 475A suggests that this will be a quick diagnosis.

Looking at the schematic, (<12> Power Supply) we see at the bottom of the page that the LOW LINE indicator is driven by the unregulated +55V rail and the -8V rail. It looks like there's a voltage divider between +55 (unreg) and -8 V rails, but my circuit analysis knowledge breaks down at about that point. I'd check the voltages on the +55 V UNREG (TP1536?) and -8 V (TP1568) rails first, then, if those look good, check Q1582.

I'm a little confused by the schematic (as simple as it is) because they seem inconsistent in whether they label the test points with the expected voltage, and whether they indicate what voltages are unregulated. I can't tell if TP1536 is the same as the +55V UNREG indicated in the partial A8 schematic at the bottom of the page. This would all be much easier to clear up if I had the scope in front of me.

Good hunting

-- Jeff Dutky
Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

 

Thank you very much Chuck, I will not make the change to bring it to 2.5 GHz, instead I wanted to ask you what is the real analysable minimum frequency, I have seen that approaching 1 kHz it becomes difficult to visualize the signal due to the proximity of the internal local oscillator carrier .

As for the Tuning control, I assure you that everything looks original and on the front there is only the word TUNING and not PUSH / PULL.
I don't know what to say about it.

Greetings
Attilio
Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

 

This a.m. I got a delivery from Amazon of some very nice bench equipment: 50 ohm RG58 cables and (I don't know what the spec is off the top of my head skinny copper colored) SMA/BNC cables with lots of BNC and SMA connectors & Tees. After the normal morning noodling I came down to the bench to try the new toys out and got a 20mV signal going on CH1 and CH2 of my parts scope. I was going to take pictures of the setup showing how perfectly matched everything was: 20mV on each channel of signal generator producing exactly 4 divisions on each channel of the parts scope so perfectly overlapped that you couldn't tell the difference between CH1, CH2, and both, CHOP or ALT, aligned to the same ground. I was very pleased with myself.

But life called and I went back in to organize this afternoon's Christmas shopping trip with my daughters. As it turned out they needed another 30 minutes to get ready, so I came back to the bench to get the pictures. I'd shut everything off, and when I turned the parts scope on it did not produce a trace. Uh-oh. Then I noticed the "LOW LINE" light on it.

This is what it did when I first powered it up after the tear-down, repair, and rebuild I did. I believe I wrote something about that before on here and someone said "beware problems that magically go away". Bingo. It's not coming back on. Maybe this is my chance to fix something else wrong with it that may have lead to it's demise.

Dave

On Tuesday, December 22, 2020, 04:12:25 PM PST, Jeff Dutky <jeff.dutky@...> wrote:

I spent some time in theater in high school and college, and gained an unhealthy sense of superstition from the experience. Bad luck is ALWAYS contagious.

How did it die? Are there symptoms (other than being dead)?

-- Jeff Dutky
Re: Thoughts About Modern Tek Scopes

 

Hi Jeff-

I have no interest whatsoever in the current oscilloscopes, from anybody. You said a mouthful about not expecting the same user experience that you're used to with classic Tektronix analog instruments. As long as I can keep my 7934 and 7104 running, they'll continue to be my heavy hitters. My favorite, when bandwidth is sufficient, is a 555. The ultimate user experience! :-)

I keep a 7633 handy as well. Quick to use and a beautiful display! I really like the fact that I am looking at the actual signal being displayed and can make my own assessments, rather than having the computer in the scope looking at the waveform and telling me what it thinks it sees.

Just my thoughts....

Tom
Re: SUCCESS! The "sick" 475A is now the "fixed" 475A!

 

I spent some time in theater in high school and college, and gained an unhealthy sense of superstition from the experience. Bad luck is ALWAYS contagious.

How did it die? Are there symptoms (other than being dead)?

-- Jeff Dutky
Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Chuck Harris
 

I can't say about the push/pull tuning knob, only that it is easy
to break, hard to fix, and adjust... perhaps yours got broken and
this is the best fix easily done?

I think what you are looking at is a 7L12 knob, and perhaps
everything behind it.

The 7L13 has a high IF frequency of about 2.5GHz. The 2.5GHz
modification removes the roofing filter from the RF input, allowing
signals up to 2.5GHz and beyond to enter the mixer... Without the
roofing filter, these signals pass right through into the IF
amplifier, where they lift the entire band.

Basically, you can count on seeing your router, bluetooth, and your
microwave oven take over your SA whenever they happen.

I wouldn't want a 7L13 with the 2.5GHz modification.

It is a nice little SA, best keep it nice.

-Chuck Harris

Attilio wrote:

Dear Sirs,
I got hold of a 7L13 spectrum analyzer in a 7603 mainframe and I have two questions to ask you, first from the manual the tuning knob can be pushed or pulled to change the tuning speed, but on my 7L13 the tuning knob is fixed and there is only the word tuning,
Do you know when this modification was made and why ?
Second question: Is it possible to extend the maximum frequency from 1.8 GHz to 2.5 GHz ?
If so, what are the changes to be made ?

Thanks a lot to everyone, a greeting
Attilio
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