Date   

Re: Tek 4041 GPIB Controller

Monty McGraw
 

We can get the 4041 service manual scanned from the vintagetek.org microfiche library of all Tektronix documentation - after COVID-19 is over. Right now Oregon is still in lockdown. They only charge $25 an hour for scans.


Re: Advice about buying a 7904

Sean Turner
 

Reg,

As you may know from our prior conversations, I have both a 7104 and a 7904A. The 7904A is definitely my workhorse because, as you mention, I want to preserve and protect the mcp tube in the 7104. As Dave mentioned, the chassis is different between the 7904 and 7904A. The 7904A is going to be easier to work on from an access perspective. One thing the 7904 has that I wish the 7904A carried on is a current loop calibrator for current probes. Oh well. Another thing to keep in mind is that the 7904A uses the hypcon packaged hybrids like the 7104 in the vertical amp[1], while the 7904 does not.

As far as reliability, I would imagine both have tantalum capacitors. Since these scopes have a switch mode power supply, it's easy to tell when you have a short because you get the infamous clicking as the supply tries to turn off then shuts down. Finding the short is another matter, though fortunately for me the short my 7104 developed when I got it home from the auction house turned out to be super simple and not tant related at all.

As far as plugins go, the 7A26 is a perfect vertical option for general purpose work. There's a couple different revisions hanging about. Some have a 20 MHz bandwidth switch and some do not. I have examples of both. Honestly, the one that doesn't have it has a sharper trace all around in my experience. Use two of them and have a full on 4 trace scope. The 7A19 is a good match for the mainframe if you want a vertical with a dedicated 50 ohm input. Keep in mind that unlike the 7A29's circuit breaker arrangement, the 7A19 uses fuses for input overload protection. Still useful for specialty probes that expect 50 ohms, such as current probes. Another vertical plugin in find indispensable for low frequency work is the 7A22 differential amplifier. Even single ended with a 10X probe, you can get down into microvolts/div ranges and the adjustable bandpass filter is very useful for isolating signals in noise. I have a 7B15 and a 7B92A as timebases in mine; no complaints.

[1]: http://w140.com/tekwiki/wiki/7904


Re: Advice about buying a 7904

Dave Daniel
 

The 7904A is easier to wotk pne because it has the “kickstand” feature where one can split the display section up off of the lower section to make repairs. I’ve never compared the specs of a 7904 and 7904A. I imagine they are quite similar. I’d probably buy a 7904A if I had to choose. As far as I know there are well-known problems with either ‘scope.

If it were me, I’d also consider a 7854.

Selecting plug-ins is a pretty deep subject. 7A26s with 7B92s is a good choice for general purpose work. IIRC, 7A19s are 50 ohm input only.

Once you get a 7xxx ‘scope you will probably want to get a differential amp, pulse and counter plug-ins as well. It’s a rabbit hole.

DaveD

On May 28, 2020, at 18:50, Reginald Beardsley via groups.io <pulaskite@...> wrote:

I have a 485 and a 7104. The onlyfragile CRT of the latter discourages regular use unless needed. Reed refurbished my 485 and obviously it's a really fine instrument.

I'm mulling over getting a 7904 for more routine work because I find the overshoot on DSOs very annoying. My 1.5 GHz LeCroy has a spec of 17% overshoot. I don't consider anything above 2-3% acceptable. I've asked Tek for a step response for a 3 or 4 series 1 GHz DSO using one of Leo's pulsers or similar. After my adventures with Keysight's MSOX3104T and the Rohde & Schwarz RTM3104 I don't want to get a demo unit unless it has an acceptable step response. It will be interesting to see if I get one.

I've never touched a 7904 and have no knowledge of them other than what I've read on TekWiki.

So some questions:

which is the best choice from a long term support basis, 7904 or 7904A?

what plugins? 2x 7A19 and 7B92 + ???

common issues (e.g things like the 576 transformer problem)?

anything else?

Thanks,
Reg



Advice about buying a 7904

Reginald Beardsley
 

I have a 485 and a 7104. The fragile CRT of the latter discourages regular use unless needed. Reed refurbished my 485 and obviously it's a really fine instrument.

I'm mulling over getting a 7904 for more routine work because I find the overshoot on DSOs very annoying. My 1.5 GHz LeCroy has a spec of 17% overshoot. I don't consider anything above 2-3% acceptable. I've asked Tek for a step response for a 3 or 4 series 1 GHz DSO using one of Leo's pulsers or similar. After my adventures with Keysight's MSOX3104T and the Rohde & Schwarz RTM3104 I don't want to get a demo unit unless it has an acceptable step response. It will be interesting to see if I get one.

I've never touched a 7904 and have no knowledge of them other than what I've read on TekWiki.

So some questions:

which is the best choice from a long term support basis, 7904 or 7904A?

what plugins? 2x 7A19 and 7B92 + ???

common issues (e.g things like the 576 transformer problem)?

anything else?

Thanks,
Reg


Re: 475 questions

teamlarryohio
 

IIRC, only the 432, 434, and 485 had switchers.

The 485 was much like a 7K with the Tek-made controller chip. The 43X's
were discrete.

-ls-


Re: 475 questions

ciclista41@...
 

Hey guys! Look at me with my newly acquired acronyms! ;-)

On Thu, May 28, 2020 at 03:39 PM, <ciclista41@...> wrote:


Still great advice for later when I'm working on a DUT with a SMPS. :-)

On Thu, May 28, 2020 at 03:34 PM, <ciclista41@...> wrote:


Excellent advice, Eric!

Now I'm glad I just put that incandescent bulb in series when I turned it on
the first time. Not that I have a variac (yet).

Bruce

On Thu, May 28, 2020 at 12:53 PM, Eric wrote:


I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one
transistor
so far that has "kind of" failed that one took a 576 to find it, was out
of
a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a
variac.
The 400 series have switching power supplies they are not the linear
supplies
They can over current when the line voltage drops to low to regulate and
can
be damaged. Slow up on a varic is ONLY good for linear power supplies.


Re: 475 questions

ciclista41@...
 

Still great advice for later when I'm working on a DUT with a SMPS. :-)

On Thu, May 28, 2020 at 03:34 PM, <ciclista41@...> wrote:


Excellent advice, Eric!

Now I'm glad I just put that incandescent bulb in series when I turned it on
the first time. Not that I have a variac (yet).

Bruce

On Thu, May 28, 2020 at 12:53 PM, Eric wrote:


I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of
a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear
supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.


Re: 475 questions

ciclista41@...
 

Hi Eric,

Must they be removed from the circuit to get decent readings? If so, I'll do it. This thing seems to have been designed to make it easy to remove them once the large caps are removed.

Bruce

On Thu, May 28, 2020 at 12:53 PM, Eric wrote:


I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.


Re: 475 questions

ciclista41@...
 

Excellent advice, Eric!

Now I'm glad I just put that incandescent bulb in series when I turned it on the first time. Not that I have a variac (yet).

Bruce

On Thu, May 28, 2020 at 12:53 PM, Eric wrote:


I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.


184 Time-Mark Generator lamp

Sean Turner
 

Hi all,

I recently acquired a rather nice shape 184 for the princely sum of $70. After some good burn in and exercising the controls following by a few adjustments, it ticks along perfectly except for the HF oscillator (but that's beyond the scope of this topic) and the green power lamp (above the oven lamp, which is working), which is burned out. I was surprised to find the bulb is one assembly that plugs into the socket. I assume these are probably unobtainium, but would be interested in being contacted off list if someone has one they are willing to part with.

Thanks!

Sean


Re: Trying to save a 576

Martin Whybrow
 

One of the things being added to my workshop is a vacuum system that would be suitable to pump down a CRT, but I wouldn't entrust myself to a CRT as rare as the one in the 576 as a test candidate! I can live with the burned spot for now, but thanks for the offer.


Re: probe.

Roy Thistle
 

From what I've read...Tek took a systems approach with this series of 2400 scopes... so it's fair to consider a 2465B scope plus the Tek recommended P6137 as what Tek intended... when interpreting the Tek specs about them.
Taking that way of looking at it... the DUT is on one end of the system, and you are on the other... and so what you see is what you get.

I've a feeling that Tek enthusiasts might buy a Tek scope just based on the nominal bandwidth, and then look for probes with a matching nominal bandwidth.
Given just the above, and assuming too, that the front end, filter response, of a 2465B is Gaussian, then:

(1) BW(system) = 1 / sqrt[ 1/(probe bandwith ^2) + 1/(scope bandwidth ^2) ]

So from (1) it is easy to see... if the bandwidth of the scope and the probe match... the nominal bandwidth of the system is scaled by 1/sqrt(2)
Thus, for a 400 MHz nominal bandwidth... (1) gives a system bandwidth of approximately 282 MHz. (Check the calculation!)
For a 2465B... that's a "sweet spot" in the sense that reducing the nominal bandwidth of the probe is only going to reduce the system bandwidth... but given the high non-linearity of (1), its not a proportional reduction.

So consider using a probe with a nominal bandwidth of 100 MHz. Then (1) gives a system bandwidth of approximately 97 MHz. That is pretty close to the nominal bandwidth of the probe.

The takeaway from (1) is that just considering bandwidth specs... if you are working on 10 MHz timebase, with a 2465,B... say just for the features that Tek offers.. then using a P6105 probe is probably okay. (I say probably...because Tek specs a P6105 for 15 pf, on the lower end of the compensation... and Tek specs the input of some? 2465Bs at 15 pF + - 2 pF.)

Best regards and wishes.
Roy


Re: 475 questions

Michael W. Lynch
 

Raymond,

Thanks for verifying. I thought that I knew these scopes pretty well. But I have been wrong before and it would not have been the first time that I stuck my foot in my mouth.

I have a TDS360 and TDS460A and those both use the SMPS design, but totally unrelated to the 4xx Series.

--
Michael Lynch
Dardanelle, Arkansas


Re: 475 questions

 

On Thu, May 28, 2020 at 10:36 PM, Michael W. Lynch wrote:


I am pretty certain that the 455/465/475 use a linear power supply.
That is correct.

Raymond


Re: 475 questions

Michael W. Lynch
 

However do NOT bring up a 400 series scope slowly on a variac. The 400 series have switching power supplies they are not the linear supplies They can over current when the line voltage drops to low to regulate and can be damaged. >Slow up on a varic is ONLY good for linear power supplies.
Eric,

I am pretty certain that the 455/465/475 use a linear power supply. That is the purpose of the big heavy transformer in the back of the scope. If it was a SMPS then there would be no need for that heavy beast.
--

Michael Lynch
Dardanelle, Arkansas


Re: probe.

 

On Thu, May 28, 2020 at 08:36 PM, Jim Ford wrote:


I was able to adjust the probe to get a nice flat response when connected to
the calibrator on the 54504A. Fortunately it also looked flat with the
calibrator on my Tek 7904.
Hi Jim,
The artifacts that I was referring to don't show up on standard 'scope calibrators. Those only allow you to adjust "LF" behavior with a 1 kHz square wave (flat top).
I meant fast-edge behavior, like that visible with <=1 ns steps in the first few ns or in the edge itself. That's where the differences are. You won't just see a flat or single-curved top but all kinds of ripples, resonance-like behavior etc. I know about only one "classic" Tek 'scope that offers that kind of fast step: the 485 in addition to a nice 1 kHz square wave. It allows LF adjustment *and* HF adjustment. The latter is done with separate adjustment regulators in the compensation box of the probe, underneath the plastic cover. *And* you need a well-matched input to the probe, like a probe-shaft-to-BNC adapter
The calibrator's edges in the 7904 are no faster than 250ns so they are useless for showing the differences between e.g. the P6139A and P6137, much less perform the HF adjustment I was referring to.


And I'd check the input capacitance of the scope (7 pF in the case of the 54504A) versus the output capacitance of the probe (8 pF in the case of the P6139A), and
if they are close, you will probably get good results when you connect the probe to the calibrator and adjust it for flatness.
That's not correct: 8 pF is the nominal *input* capacitance of the P6139A and they don't have to be nor will be equal. Otherwise, you wouldn't be able to adjust an 8pF or 1.5 pF FET input capacitance probe to several different 'scopes, like the 2465B with its 15pF nominal input capacitance or a 7A26 with 22pF nominal. It's all about RC times, probe input, cable, probe output, 'scope input. The publications I referred to show it all.

Nothing to worry about for general 'scoping in the sub-100MHz domain though. Who said that 100 MHz actually is DC?

Raymond


Re: 475 questions

Eric
 

I would test the rectifiers the silicon is usually pretty resilient and normally grossly fails "open or short". I have only run in to one transistor so far that has "kind of" failed that one took a 576 to find it, was out of a fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac. The 400 series have switching power supplies they are not the linear supplies They can over current when the line voltage drops to low to regulate and can be damaged. Slow up on a varic is ONLY good for linear power supplies.


Re: 475 questions

Eric
 

Bruce,
Another critical peace of advice. Before you tare something down take a TON of picture from ALL angles. This will aid you in reassembly. A digital camera in the lab can save you hours in a schematic when you have a 50/50 shot of getting a power plug backwards and popping something. Also however many picture you THINK you need take double invariably there will be an angle you are missing that you need.

Eric


Re: Trying to save a 576

Eric
 

Martin,

    Unfortunatly I can answer that. I have the tube in question it is weak. It is doing a double ramp but this one is slightly weak. I have a second tube as well that is VERY weak. I have not looked in to rejuvination of these or rebuild yet let me know if you are interested They came to me at cost of shipping and I am more then happy to pass them on for cost of shipping.

Eric

On 5/28/2020 5:35 AM, Martin Whybrow wrote:
Ryan, has that CRT been taken? If not, I would be interested, does the screen appear burned? My 576 works, but has a completely dead spot where the intensity was left too high with a static spot displayed.


Re: probe.

Jim Ford
 

I agree. I recently grabbed a P6139A out of Raytheon Technologies (RTX, my day job) e-waste bin and found that it works well with my 400 MHz HP 54504A scope (also an RTX rescue). I was able to adjust the probe to get a nice flat response when connected to the calibrator on the 54504A. Fortunately it also looked flat with the calibrator on my Tek 7904.

So, yes, for most purposes a properly adjusted 500 MHz probe will work with a 400 MHz scope. If you're testing pulses up near the limit (handy rule of thumb is pulse rise/fall time is 0.35/3 dB bandwidth), say 0.9 ns (about 400 MHz 3 dB BW), then no, you won't get an accurate picture unless you use the probe specifically designed for the scope. Also handy to remember 1 ns rise or fall time is equivalent to 350 MHz 3 dB BW, and 1 GHz BW is equivalent to 0.35 ns rise or fall time.

And I'd check the input capacitance of the scope (7 pF in the case of the 54504A) versus the output capacitance of the probe (8 pF in the case of the P6139A), and if they are close, you will probably get good results when you connect the probe to the calibrator and adjust it for flatness. Sometimes you can even find the range of capacitance of the probe. The HP 10430A probes I have with the 54504A scope say "1 Megohm||6.5 pF for 1 Megohm||6-9 pF inputs" on them. Also check http://w140.com/tek_probe_crossref_1990.pdf to see what probe(s) go with what Tek scopes.

There's more, but it's probably covered in those references Raymond mentioned.

Good luck!

Jim Ford

------ Original Message ------
From: "Raymond Domp Frank" <hewpatek@...>
To: TekScopes@groups.io
Sent: 5/28/2020 4:49:56 AM
Subject: Re: [TekScopes] probe.

On Thu, May 28, 2020 at 07:40 AM, James Theonas wrote:


Is this probe a good match for my scope?
It would be insofar as bandwidth is concerned. The transient response however is not matched to the input characteristics of the 2465B. It'll work but signal fidelity will not be optimal, resulting in visible step response artifacts. For the 2465B, Tek recommended the P6137. With the right tools and equipment, you could optimize the behavior of the probe with its high-frequency adjustments.

Raymond


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