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On 3/28/2021 4:15 PM, Maurizio IZ1MDJ wrote:

On Sun, Mar 28, 2021 at 09:32 PM, Mlynch001 wrote:

On Sun, Mar 28, 2021 at 01:32 PM, Maurizio IZ1MDJ wrote:

I am looking for information about a TEKTRONIX model 2215A oscilloscope.
It is an analog oscilloscope with digital memory and I have not found any
information on the TekWiki site.
In particular I am interested in the use and service manuals.

I have a 2215A. The 2215A is not a digital memory scope that I know of, it is
a simple analog design. 2215A is an improved version of the original 2215.
The manuals you want are indeed listed on Tekwiki140. Here is the page link:


Schematic and operators manuals are there as well.

Have fun.

--
Michael Lynch
Dardanelle, AR

If you take a look at the picture of the scope in the gallery ( as I wrote )
you can see that the scope has the memory control pusbutton in the front panel
Maurizio IZ1MDJ

What do you think is the "memory control pusbutton"?

On Sun, Mar 28, 2021 at 09:32 PM, Mlynch001 wrote:

On Sun, Mar 28, 2021 at 01:32 PM, Maurizio IZ1MDJ wrote:

I am looking for information about a TEKTRONIX model 2215A oscilloscope.
It is an analog oscilloscope with digital memory and I have not found any
information on the TekWiki site.
In particular I am interested in the use and service manuals.

I have a 2215A. The 2215A is not a digital memory scope that I know of, it is
a simple analog design. 2215A is an improved version of the original 2215.
The manuals you want are indeed listed on Tekwiki140. Here is the page link:


Schematic and operators manuals are there as well.

Have fun.

--
Michael Lynch
Dardanelle, AR

If you take a look at the picture of the scope in the gallery ( as I wrote )
you can see that the scope has the memory control pusbutton in the front panel
Maurizio IZ1MDJ

I have a 2215A myself, and that one is purely analog.

I've never seen a 2215A with the addition 'Storage'...

My guess: it has an analog storage CRT...

Leo

FWIW In the event that you have a system on which the calibrator output is not working, if you connect the "Internal clock output" to an input and set the trigger to "internal" you should get a proper square wave, though at ~1 ns rise time in my case. Spec is <2 ns in the service manual. You can also verify the clock signal to the calibrator by connecting the 3.5 mm series coax to a sampling head. It should look just like the "internal clock" front panel output.

I'd like to note that I count 4-6 push on connections from the sampling head to the card cage boards. so there is lots of room for a fault which can be cured by reseating the connectors. Though a bit of PITA to get at some of them.

NB: I'm using an SD-22 for working on this. Nominally that's a 30 ps rise time head.

Reg

On Sun, Mar 28, 2021 at 01:32 PM, Maurizio IZ1MDJ wrote:

I am looking for information about a TEKTRONIX model 2215A oscilloscope.
It is an analog oscilloscope with digital memory and I have not found any
information on the TekWiki site.
In particular I am interested in the use and service manuals.

I have a 2215A. The 2215A is not a digital memory scope that I know of, it is a simple analog design. 2215A is an improved version of the original 2215. The manuals you want are indeed listed on Tekwiki140. Here is the page link:

Schematic and operators manuals are there as well.

Have fun.

--
Michael Lynch
Dardanelle, AR

In an attempt to get access to the calibrator I removed the nuts holding it in place per the service manual instructions. In the process I made a major tactical error and dropped one of the nuts into the instrument!

If you need to remove the calibrator for any reason, loosen the nuts and then use a multi-prong grabber to remove them. It's also advisable to have the instrument resting with the RHS on the bench. That will prevent the nuts from falling into the instrument.

As a consequence I now have both covers off the instrument at the same time. Fortunately, the nut fell out when I rotated the instrument.

The calibrator pin header is connected to J91 on Timebase Controller which is much more accessible for probing.

brown ???
red +4.93 V
orange ???
yellow ground
green ???
blue -4.93 V
purple ???

I have a clean square wave on the 3.5 mm line going to the calibrator. Does anyone know what signals should be on the brown, orange, green and purple wires? All I see with a scope is mV level noise.

Access to the signal path is through the RHS and the top. Both covers have to be off. The far RHS board is the TDR/Strobe buffer. The sampling heads plug into an interconnect board via ribbon cables. It's unclear from the manual if you can reseat the connectors in the signal path from the RHS after removing the TDR/Strobe buffer. But that looks to be the case. As I don't have signal path issues I don't want to mess with it.

I pulled the I/O board. As I expected the self test was turned off. In fact, all the jumpers were set to zero. I set them all to 1 in hopes of getting 19,200 baud on the RS-232 port, but it still reports 9600. Does anyone know if they will actually do 19,200?

I'm now throwing a T1331 error. That should be cleared if it boots normally. I saw this with #1 after I replaced the NVRAM. Do I need to jumper this to not halt on an error and then rejumper it? Pulling the card from the cage is a PITA. I remember the error from when I replaced the NVRAM in #1, but it cleared after a couple of boots. In this case, that is not happening. #1 is on a shelf 4+ ft from the floor, so I really don't want to wrestle it down to take apart to compare stuff.

Reg

Thanks. For now I'm trying to achieve the fastest possible risetime and a not-too-ugly flat top. I have somewhat achieved that already.... I can reduce the overshoot and ringing by adjusting the trimmer cap. I have a calculated 380 ps 10-90% risetime now. What might a few ohms in series with the charge line do to that? (The 2N2369 did give a cleaner output as in the earlier photos, but only about 650 ps risetime).

I left the neatly-cut end of the .141 line open. If I wanted to continue over-stuffing this Minibox I could solder an SMA connector to it and add another piece of line. But I also don't want to overtax the BFR505 which is pulsed every 2 us. At slower rep rates (relaxation osc mode), other experimenters were seeing failures in a few hours with longer pulses than 16 ns...

I remember your previous advice on matching and dynamic impedance changes. By trial and error I found that paralleling another 100 ohm emitter resistor (i.e. 33 ohm emitter load) improved everything except output amplitude, of which there is still plenty (6-7 volts). All these traces are: SMA output, SMA-GR adapter, GR 10x attenuator, 3' of GR 50 ohm cable into the 50 ohm sampling head. So any mismatches in the cable or sampler should also be attentuated on reflection.

When removing the cable and plugging the attenuator directly into the head, the persistence of the ringing through the whole flat top is now visible without the cable attenuation... As expected, the risetime improved also (but naturally the overshoot is worse). 320 ps displayed (310 corrected) without the cable. 380/370 with it.

I am looking for information about a TEKTRONIX model 2215A oscilloscope.
It is an analog oscilloscope with digital memory and I have not found any information on the TekWiki site.
In particular I am interested in the use and service manuals.
I uploaded a photo of the scope on TEK2215A album
Thanks in advance
Best Regards
Maurizio IZ1MDJ

You can smooth out the flat-top by adding a little series R from the emitter to the output cable connection. This will trade some edge speed for more civilized appearance afterward. Remember, nothing is really impedance matched here, so trade-offs need to be made, depending on what features are needed. If the goal is to get more flatness and pulse width for viewing lower speed scope performance, the rise time and amplitude are probably plenty good enough already, so you can give some up. I didn't notice in the discussion anything about provision for pulse extension, just that there's about 6 nSec of 141 line inside. Do you have the open end of the charge line going to an SMA connector for external line? That would take care of pulse width, so cleaning up the waveform is next. I'd recommend trying a small SMD series R, like from a few ohms up to maybe 22 ohms, experimentally.

Also note that there is such a thing as too fast a rise time when checking lower speed equipment. When checking scopes that are native 50 ohm input, it should be good to go, but for setups with 1 meg inputs with an added termination, there will be a number of discontinuities and reflections - the scope is mostly a capacitive load, and a very short test signal rise time will aggravate the situation. This can make it difficult to assess the response to "normal" signals the scope would encounter, although it would show what it actually does at very fast edge speeds.

Ed

True... but if this were the source of the ringing, then wouldn't I see substantially less ringing, and a corner closer to square, on the S-4 25 ps sampling head compared to the S-2 (75) or S-1 (350 ps) heads? The S-4 and S-2 traces look basically identical, and the S-1 looks bandwidth-limited ("softer" corner and ringing) as I expected...

Thank you folks for an interesting and informative discussion.

Clearly, there is not a general consensus regarding whether or not negative feedback reduces noise. There seem to be many who believe that it does.

A simple Google search for "negative feedback amplifier advantages" returns these hits on just the first page:



Negative feedback also has effects of reducing distortion, noise, sensitivity to external changes as well as improving system bandwidth and input and output impedances."



There are some advantages of negative feedback amplifier which are given below,

The negative feedback reduces noise.
It has highly stabilized gain.
It can control step response of amplifier.
It has less harmonic distortion.
It has less amplitude distortion.
It has less phase distortion.



Negative feedback has following advantages:

? The negative feedback reduces noise
? It has less frequency distortion means improved frequency response
? Better stabilized voltage gain
? It has less harmonic distortion.



The use of negative feedback can discriminate against sources of noise or distortion within an amplifier.

-------------------------------------------------

So, in attempting to understand the issue, suppose I have a need for an amplifier with a gain of 20 dB but the device I am using has a greater gain so I build three test circuits.[Lab assignment]

For the first circuit, I achieve the gain target by adding negative feedback. For the second circuit, I achieve the gain target by adding input attenuation. For the third circuit, I achieve the gain target by using output attenuation.

Each of these circuits will have a noise figure that reflects the difference between a given S/N at the input and the S/N at the output.

The circuit with the best noise figure is?

It might just be the math. You cannot get
a perfectly flat top even with infinite bandwidth...

Look up Gibbs Phenomena.

Basically, the Fourier combination of sine waves to
create a square wave will never quite get to a perfect
square, because there will be spikes and ringing at the
discontinuities.... even if you go out to infinite bandwidth.

-Chuck Harris


On Sun, 28 Mar 2021 09:23:01 -0700 "Charles"
<charlesmorris800@...> wrote:

That is true, but Bodnar's pulser is a full order of magnitude faster
than mine (30-40 ps vs. 380) and I'm sure nothing is what it seems at
that speed.

Anyway, I may just stop here rather than drive myself nuts trying to
get a perfect square pulse! It's faster than any of my scopes can
measure except the sampler. On my 7A26/7403 (the amp is 200 MHz but
the mainframe only 65 MHz) I just see a little 1 volt rounded bump a
few ns wide ;)

Thanks nj902, I understand.
But I read in the 492P manual that it can transmit the data relating to the waveform in ASCII format, perhaps with a suitable program on a PC they could be converted into a plot type graph ... perhaps?

--Cheers
Attilio

That is true, but Bodnar's pulser is a full order of magnitude faster than mine (30-40 ps vs. 380) and I'm sure nothing is what it seems at that speed.

Anyway, I may just stop here rather than drive myself nuts trying to get a perfect square pulse! It's faster than any of my scopes can measure except the sampler. On my 7A26/7403 (the amp is 200 MHz but the mainframe only 65 MHz) I just see a little 1 volt rounded bump a few ns wide ;)

I don't have an answer, but I would note that the Leo Bodnar Fast Risetime Pulse Generator also has some ringing at the start of the flat top, and its circuit construction is extremely compact, so it might be due to something other than lead lengths.

When Tektronix introduced the 492, it was an advance in technology to offer so much capability in such a small package. The 492P model includes a GPIB interface for remote control.

The 492 platform became the foundation for subsequent models with additional capabilities. The 494 introduced drift free operation with an internal reference, direct keypad entry of frequency and other parameters, and with the 494P, the ability too directly plot the screen contents to an attached plotter.. That capability continued in later models such as the 492AP.

Unfortunately, since the 492P came first, it doesn't have the direct plot capability.

Any thoughts on what's causing the ring with the 2 ns period at the start of the flat top?
Maybe the short but unavoidable length of exposed center conductor where the charge line connects?

I wanted to write 492P, it's not a day.

--Cheers
Attilio

oops, sorry.
This is a 429P not a 492AP, I was wrong.