Re: 7A16A high frequency compensation.
Thank you Raymond. I just looked briefly at internet too see whether or not it could do random sampling.
Charles can forget my inappropriate warning.
Albert
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Re: Recapping Tektronix 2465
I do have kits available, which I custom assemble, to suit your EXACT machine.
I'll need CLEAR photos of your A1 A2 A3 A4 A5 A9 A14 PCB's
Saves you the time and hassle of sorting and sourcing, and wondering if you made the correct choices.
Here's the ebay ad
Forum members who buy via my contact directly here (NOT via ebay), get a 15% discount.
Yachadm AT gmail DOT com
CondorAudio
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Re: S-1 transient response problems
Using double diodes changes a lot of the conditions. Try going back to single diodes instead of series doubles, and see how it works. You can temporarily short one of the diodes in each pair for experimenting. There may not be enough strobe drive - it may be adjustable and fixed that way. Also, check the other adjustments and study their purposes and effects.
Ed
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S-1 transient response problems
You may recall that I have an S-1 sampling head with blown diodes, which I replaced with M/Acom MA4E1339 Schottky diodes in SOT-323 packages. I used both diodes in the package in series, max 1.2 pf each, to keep the capacitance down. They are mounted on small pieces of copper-clad and the package spans a gap in the copper. Hopefully low capacitance.
Anyhow, it works fine on fast pulses, and at DC too. But I ran a 1 MHz square wave through it (something I would not normally use a sampling scope for) and found that the transient response is waaaaay undercompensated. There's a bad overshoot, then undershoot, finally recovery. Per the S-1 manual that is the input to use while adjusting the transient response. But there isn't enough range on the pot (R13) to get it near flat, although with it all the way "up" it's better. I'll post display pics tomorrow.
I conclude that either my mount has excessive capacitance causing blowby in that frequency range, or possibly Q13 is bad. Although the trigger pickoff does function (Q13 drives Q17 which sends the trigger to the 3S2). It will be difficult to make a mount with much less C... the diodes themselves, at 0.6 pf, should not be a problem.
So I could use some suggestions. If I have to modify the circuit to allow for more out-of-phase signal to bypass the sampling bridge, what would be easiest to change with minimal side effects? Thanks.
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Re: FG502 doesn't start at some specific settings
Both marked 820 ohms (grey-red-brown); initial measure in circuit R155 real
value 1053 ohms (same value when removed), R290 real value 832 ohms and they
look like 0.5W (if not more). Now the two have places switched, but, as I
said, no difference in behavior of the stage
It is better to place the proper value, 820-ohm nominal, in both places. Voltages look OK ballpark. Perhaps some of the transistor gains decreased over time and now positive feedback coming back through C247 is not strong enough. I assume your serial number doesn't have the R247 resistor parallel to C247 given R155/R290 were 820-ohm nominal. You could try adding another 2.7pF in parallel with C247 to see if it helps. Note that C247 was selected so its value is critical to proper operation. At the higher frequency settings (higher charge/discharge currents) slight mismatches in source and sink current may be flowing into R155/Q292 junction and place the operating point in the bad stable condition. Looking at the min/max voltages at Q292 collector in normal operation in those high frequency settings may give other clues. Ozan
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Re: 485 super weak brightness control
Tomorrow I'm going to make a table with gate times both A and B at each
setting.
I observed today the gate width was same as 1ns on 10ns and 100ns, there
must be some logical explanation for that? Can't think of an easy explanation. When you are making the table could you also mark down both A gate width and B gate width while you are measuring B sweep timing? Also please observe if you really see a fast sweep when gate is shorter than expected or if the gate is cut short. If you apply a signal you can tell from the screen whether sweep is complete but fast or if it is truncated. Ozan
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Re: 7A16A high frequency compensation.
On Tue, Mar 23, 2021 at 11:44 PM, Albert Otten wrote:
The PM3340 only does sequential sampling and requires signal delay..
My PM3340 has a signal delay line... Trigger pickoff right at the N-socket and a nice blue Suhner coax cable after that for each channel. Nice but very heavy beast. Raymond
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Re: 7A16A high frequency compensation.
Hi Max,
It's nasty that the PG506 trigger output is not usable as pretrigger. Also (e.g. in my PG506) there is too much between-trigger jitter to view the fast edge of the next pulse. That's why a 7M11 delay line is used in the calibration section. But the 7M11 is not ideal. Hence the PG506 signal output waveform is compared with a faster TD pulser waveform. The PM3340 only does sequential sampling and requires signal delay..
BTW I found that the fast-rise rise time depends a lot on the amplitude, something like 0.75 ns for low to 1 ns for max amplitude.
Albert
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On Tue, Mar 23, 2021 at 10:23 PM, unclebanjoman wrote:
Hi Albert,
you made me doubt about the PG506 now :-)
I would not like to have calibrated the 7A16A trying to compensate for the
aberrations of the PG506 itself.
In the weekend I'll check the fast rise output of my PG506 using the
3S11/3T77A and also with a 2 GHz Philips PM3340 that I received a month ago
(fully functional, like new).
I'll post some photos as soon as possible.
Max
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Re: 7A16A high frequency compensation.
Hi Albert,
you made me doubt about the PG506 now :-)
I would not like to have calibrated the 7A16A trying to compensate for the aberrations of the PG506 itself.
In the weekend I'll check the fast rise output of my PG506 using the 3S11/3T77A and also with a 2 GHz Philips PM3340 that I received a month ago (fully functional, like new).
I'll post some photos as soon as possible.
Max
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Interesting HP production test fixture, even Tek guys will like it.
Every so often, I get some intriguing test gear from inside places that make test gear. It's fascinating to see what they use themselves. I just overhauled and posted such an item, an HP K09-0982B, a variable 115/230V AC Power supply, used to check the effects of different AC supply voltages on finished gear. Since many here often discuss slowly ramping up the AC to items that have been sitting a long time, I thought it might be of interest. you can see it here:
I also have some other strange HP fixtures used to control a large series of AC outlets with serial commands, for controlled power cycling, presumably for reliability testing. I haven't posted it up yet, but let me know if anybody finds that interesting. There's lots of weird microwave bits on the stuff season page too, so wander around, you may find something you like, which will make Susan very happy if it leaves here.
Let me know any requests, always happy to put up things people are actually interested in.
all the best,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.
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Re: 485 super weak brightness control
History is entirely unknown. I bought it for equivalent of about $20 from
guy who does disposal for universities and state own research institutes
etc. It was heading for a scrap pile.
Tomorrow I'm going to make a table with gate times both A and B at each
setting.
I observed today the gate width was same as 1ns on 10ns and 100ns, there
must be some logical explanation for that?
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On Tue, 23 Mar 2021, 20:55 Ozan, <ozan_g@...> wrote:
I must have a failed relay in the B board. Any idea what these are? They
are labeled tektronix but are they replaceable with something commonly
obtainable?
The relay doesn't change state until you hit 200ns. It could still be bad
but I don't see how it could create the behavior you are seeing. The good
news is it is on a socket, you can easily pull it off and test. While the
relay is off check for any continuity between C1443/C1442 pins to ground.
As I mentioned earlier they are three terminal caps with shield connected
to ground, which is not shown in the schematic. On my 485 there was a short
to shield.
Still the best explanation is somehow your timebase shaft is misaligned.
What is the history of this unit? May be previous owner tried to repair and
placed the shaft wrong.
Ozan
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Re: 485 super weak brightness control
I must have a failed relay in the B board. Any idea what these are? They
are labeled tektronix but are they replaceable with something commonly
obtainable?
The relay doesn't change state until you hit 200ns. It could still be bad but I don't see how it could create the behavior you are seeing. The good news is it is on a socket, you can easily pull it off and test. While the relay is off check for any continuity between C1443/C1442 pins to ground. As I mentioned earlier they are three terminal caps with shield connected to ground, which is not shown in the schematic. On my 485 there was a short to shield. Still the best explanation is somehow your timebase shaft is misaligned. What is the history of this unit? May be previous owner tried to repair and placed the shaft wrong. Ozan
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Re: 485 super weak brightness control
On Tue, Mar 23, 2021 at 08:29 PM, Ondrej Pavelka wrote:
I must have a failed relay in the B board. Any idea what these are? They
are labeled tektronix but are they replaceable with something commonly
obtainable?
K1242: They are well-known points of failure, which has been described several times, can't point you somewhere though. Have a look at TekWiki. Raymond
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Re: 485 super weak brightness control
On Tue, Mar 23, 2021 at 08:26 PM, Raymond Domp Frank wrote:
A time/div, pulse length B gate (A and B interlocked):
1 ns - 75ns
2 ns - 80 ns
5 ns - 120 ns
10 ns - 120 ns
20 ns - 230 ns
50 ns - 58 ns
100 ns - 1.1 us
200 ns - 2.2 us
500 ns - 5.5 us
1 us - 11 us
2 us - 22 us
5 us - 55 us
10 us - 110 us
20 us - 215 us
50 us - 540 us
100 us - 1.1 ms
200 us - 2.2 ms
500 us - 5.4 ms
1 ms - 11 ms
Raymond
Sorry: 50 ns - 580 ns Raymond
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Re: 485 super weak brightness control
I must have a failed relay in the B board. Any idea what these are? They
are labeled tektronix but are they replaceable with something commonly
obtainable?
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Show quoted text
On Tue, 23 Mar 2021, 20:26 Raymond Domp Frank, <hewpatek@...> wrote: A time/div, pulse length B gate (A and B interlocked):
1 ns - 75ns
2 ns - 80 ns
5 ns - 120 ns
10 ns - 120 ns
20 ns - 230 ns
50 ns - 58 ns
100 ns - 1.1 us
200 ns - 2.2 us
500 ns - 5.5 us
1 us - 11 us
2 us - 22 us
5 us - 55 us
10 us - 110 us
20 us - 215 us
50 us - 540 us
100 us - 1.1 ms
200 us - 2.2 ms
500 us - 5.4 ms
1 ms - 11 ms
Raymond
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Re: 485 super weak brightness control
A time/div, pulse length B gate (A and B interlocked):
1 ns - 75ns
2 ns - 80 ns
5 ns - 120 ns
10 ns - 120 ns
20 ns - 230 ns
50 ns - 58 ns
100 ns - 1.1 us
200 ns - 2.2 us
500 ns - 5.5 us
1 us - 11 us
2 us - 22 us
5 us - 55 us
10 us - 110 us
20 us - 215 us
50 us - 540 us
100 us - 1.1 ms
200 us - 2.2 ms
500 us - 5.4 ms
1 ms - 11 ms
Raymond
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Re: 485 super weak brightness control
What mine does is following
1 2 5 they get shorter
10 is reset to the length of 1
20 is reset to the length of 2
50 is reset to the length of 5
100 is again rest to the length of 1
200 is reset to the length of 2
Could you measure for me width of B gate for each time setting? Say from
1ms to 1ns ?
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On Tue, 23 Mar 2021, 19:12 Raymond Domp Frank, <hewpatek@...> wrote: On Tue, Mar 23, 2021 at 06:51 PM, Raymond Domp Frank wrote:
Ondrej,
Your observations re. B-gate in 1, 2, 5, 10 ns positions are as they
should
be. I guess at positions 5ns/div and faster, it says "A only" on the front
plate but I guess it actually shows B.
From what I can see in your video, all B-gate times are ok from 1 ns/div
down to 100ns/div. At longer times, B-gate is too long (belonging to 10x
faster B-times).
Raymond
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Re: 485 super weak brightness control
On Tue, Mar 23, 2021 at 06:51 PM, Raymond Domp Frank wrote:
Ondrej,
Your observations re. B-gate in 1, 2, 5, 10 ns positions are as they should
be. I guess at positions 5ns/div and faster, it says "A only" on the front
plate but I guess it actually shows B.
From what I can see in your video, all B-gate times are ok from 1 ns/div down to 100ns/div. At longer times, B-gate is too long (belonging to 10x faster B-times). Raymond
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Re: 485 super weak brightness control
On Tue, Mar 23, 2021 at 06:58 PM, Ondrej Pavelka wrote:
I used 2445B thus far, less messing with intensity to take pictures
Yeah, you used the 2467B (top one) for the latest video. I find the 2467B far less convenient for general use, especially re. brightness settings. Raymond
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Re: How to explain how negative feedback lowers noise?
Hi Keith,
Don't conflate my being didactic with being angry. Email is a lousy medium because the reader will attach an emotion track based on scant clues. That is a noisy, error-prone process.
That said, I would refer you to my initial response to the OP. Not surprisingly, I prefer my example to yours. I have taught feedback to a large collection of quite diverse audiences, and have settled on a particular set of explanations as a result of many pedagogical experiments.? I craft the particulars to match the background of the intended listener. It is very tricky to provide simple answers that also do not introduce fundamental errors.
The reason I began my response with the quote, "You cannot control what you do not measure," is that many folks have heard it before, although likely in other contexts. Even if they are unfamiliar with it, it makes intuitive sense, and it captures the essence of what negative feedback is about: You need to measure the variable to be controlled. That's necessary (but not sufficient). So in that likely familiar quote is the notion of control based on some sort of measurement of the thing to be controlled, which also then implies the existence of some sort of reference that conveys when that control is successfully achieved.
The example I offered was the thermostat. Everyone has one in the home. Everyone knows what it's supposed to do, even if the particulars of how it does what it does may be mysterious. It's a commonly encountered negative feedback system. All you have to do is point out a few of its features, and how they map to features of the quote. This simple answer to the OP's first question has all of the attributes that you enumerate, and has the added distinction of not introducing fundamental errors in the process. I teach a freshman class that has many non-EE/non-STEM students. They all grasp negative feedback's essence from the thermostat example. I had an occasion to test that explanation again this past term. And it triggers the right set of follow-on questions.
The discussion about noise wasn't a digression unrelated to the first. A proper description of negative feedback, simple or not, should set one up for answering more sophisticated questions. A poor simple explanation will align neurons in a way that actively militates against an intuitive understanding of the OP's second question (or is it the first?). Once you've got the right block diagram implicitly or explicitly implanted in their crania, adding a couple more inputs (noise or signal) to the system poses no cognitive problem. If you haven't given them the right block diagram, answering the noise question becomes nigh impossible.
So, mere simplicity is not a virtue. There's a lot of engineering that should go into crafting an answer that is both simple and correct. That kind of simple answer is scalable to address more sophisticated questions. I would go further and argue that a good simple answer stimulates precisely those types of question. A random simple answer is often a "lie that we tell to children" to get them to stop asking questions. That's bad enough, but even worse is that answering the more sophisticated questions that do get asked requires undoing the simple explanation. Why do this when there are demonstrably better alternatives?
-- Cheers
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
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On 3/23/2021 06:04, Keith wrote: re: Negative Feedback example, etc.
Folks tell me that a gentle answer turns away wrath, so I hope this is a gentle reply. I mean it in that spirit.
Tom, with respect to your criticism of my example, I would suggest that you do a quick review of the original post #1. Here is the pertinent part of it, for your convenience:
Hi all,
I'm trying to explain to people at my company (none of whom are EEs or
statisticians) how negative feedback works in a system. That's one
thing that I'm trying to get across, and I can't come up with an
explanation of it in every day terms. All the examples I find in
biology etc seem kind of dubious and not very straightforward -
there's a lot of "trust me on this" as to why it's actually negative
feedback and not some form of other regulation. What's a simple
/physical/ negative feedback?
This is question 1 in the OP...period. The core of it is simple. "...how negative feedback works in a system..." Only in the next sentence (not quoted above) does the OP then use the word "another", and only then does he bring up a second question about feedback and noise. So, the original post is really two questions. Question 1 is the issue of a real world example of negative feedback in a system. Question 2 is the interaction of feedback and noise.
Nothing in my example is intended or stated to address that second question. I had nothing to add to that discussion, and so attempted to provide the OP with his example for question one. Now I admit that the use of the word "noise" in my example does unintentionally blur the line - since I say "noisy happy children". I see how that might cause confusion, so I will attempt to edit my post to remove that word. Thanks for that.
But, to be clear here, my example was only intended to apply to question #1 in the OP. Question #1 was the only part for which I felt I had an example that met his requirements, specifically that it be;
1. "non technical" - (which I admit I assumed would mean for persons who have no electronic background)
2. use "everyday terms" (everyday means things that average people from all walks of life could grasp)
3. provide a "simple / physical / negative feedback" example.
Of course every analogy breaks down at some point, but in learning and teaching, it is quite common to go from the simple to the complex in a series of stepped examples - first simple and familiar, and therefore necessarily incomplete at some level. Then more subtle, complex, and therefore more narrow and demanding in proofs and adherence to reality.
Thanks for reading my reply in a mild spirit. I mean no disrespect, but at the moment I stand by my example (modified to remove the word "noisy" of course) as meeting the requirements of OP's question one only. Of course, if you see it differently, then perhaps we'll just have to agree to disagree on this one? In any case, thanks for your contributions to the forum. You're a valuable resource here.
Warmly,
Keith
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Raymond Domp Frank