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Is the 5.2V rail at 11V because it is unloaded ??
Dave

Bonjour à tous

Great topic, and as Dr Lee mentioned, historical links.

We must deal separately the noise of the input signal vs internals noise of the amplifier opamp, resistors, etc.

There is also the "noise gain" of the amplifier.

One can write books about this, and I reference the OP to the manual excellent texts on opamps and noise in electronic systems

if the objective is to extract a signal from a noisy input, an amplifier with or sans negative feedback will produce the same results, changes in amplitude but no effect on the SNR.

I hope this note can be useful

Bon courage

Jon

Other time bombs: there are study cases made for transporting gear. Typically they have an aluminum extrusion frame with plywood panels that have been laminated with Kydex plastic sheet, and those pieces fitted into the extrusion. The whole thing is pop-riveted together, and there are bulbous metal corners that help hold the whole thing together. The thickness of the plywood varies from 1/2" to 1/4". Generically, these have become known as Anvil Cases, after the company that pioneered their use for musical touring groups back in the 1970s. The heavier ones come with an ATA ruggedness rating. Even more generically, these are sometimes called "rock and roll road cases."

Inside the case, are sheets of polyurethane foam, cut to size to nestle the gear being transported. The case companies will make cases to fit *anything.* from a coffee maker to a Fender Twin Reverb amplifier to a Tek 7000 series scope. These cases are the gold standard for moving gear around and having it survive. Mostly.

Mostly because the urethane foam degrades over time (many years) and the byproduct of the degradation is acetic acid; i.e. vinegar. I have old cases (> 20yrs) where you can easily smell the unique vinegar smell when you open it up, and I've had gear show the signs of acidic corrosion after being stored in one of these cases. I have switched my case foam to polyethelyene foam, similar to pink antistatic foam, but black in color. It's not as soft as the urethane foam, but it does lock the gear into the case so it doesn't rattle around. I've stopped playing basketball with my cases. For smaller cases, I'm using Pelican cases instead of ATA cases, but for really large stuff and for 19" equipment racks, it's still an ATA-style case. I still use the soft urethane (ester) foam for case tops, because it is easily replaced.

I use a company in NJ who sells Pelican cases with custom made foam inserts. They use a water jet to cut the foam, and there is a CAD program online to help you define your design. For a small extra amount, they will sell you a guarantee that they'll make the foam again and again until you're happy. It's worth it. They have great prices for the Pelican (and other) cases, and the price for the foam is reasonable. There are several types of foam to choose from. This is my vendor:

--rick

Hi,

"You cannot control what you do not measure" is how I introduce negative feedback to my freshmen. An example that they all seem to get right away is a thermostat. I go from there to explaining how negative feedback solves the tracking problem ("How op-amps won WWII"), which explains the lowering of distortion, (possible) reductions in noise, etc.

But the oft-repeated claim that negative feedback reduces noise needs to be treated with great care, because it is mostly false, or at least "not even wrong". Negative feedback won't clean up a noisy input (other than by filtering, which can be provided by open-loop means with even lower noise). Because neg. fb is a tracking system, the output can't be less noisy than the input; indeed, it can only be noisier. At best, neg. fb can appear to suppress noise entering into the system near the output (because it is then tracked out). I say "appear" because an open-loop system possesses the same property, so it has nothing to do with neg. fb, per se. So, perhaps the reason you are having difficulty showing neg. fb's noise-reduction abilities is that they don't actually exist!

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

The following photos have been updated in the Sampling with 3S2 album of the [email protected] group.

• GR oscillator display with Russian D42 replacement, 750 MHz unsmoothed

By: Charles <charlesmorris800@...>

I should do the recapping of my Tektronix 2465 (not A / B), I found on this group the list produced by Menahem Yachad of CondorAudio but from Mouser (Italy) there are some parts not available.
Since I am not expert in the particular characteristics of the parts, I ask if someone can help me to choose alternative parts for these components:

Board Original Value Mouser Part# Note Warning
A3 1 uF 50v nonplzd 505-MKS2C041001FJC00 Film capacitor 1uF 63 Volt 5% not available
A1 220 uF 16v ELCTLT 647-UHE1E221MPD Aluminum-radial electrolytic capacitors 25volts 220uF 8x11.5 20% 3.5LS not available
A5 47 uF 25v ELCTLT 647-UHE1E470MDD Aluminum-radial electrolytic capacitors 25volt 47uF 5x11 20% 2LS not available
A2 10 uF 100v ELCTLT 647-UPW2A100MED Aluminum-radial electrolytic capacitors 100volt 10uF AEC-Q200 not available
A2 7.0 ohm NTC Thermistor 995-SG210 7.0 ohm NTC Thermistor 7 ohm 4 AMP minimun 2000pcs

Many thanks and cordial greetings,
Giorgio

OK, had a chance to play with it. In a word, performance is improved but still not perfect. After reconnecting the 300 ohm fixed resistor and readjusting R44 (the bias for this TD), I can now get a usable sine wave display up to 800 MHz, and even at 900 it's not too bad with smoothing enabled. Adjustment of the trigger sensitivity becomes quite critical though. Pics added to Sampling with 3S2 album, under heading "GR Oscillator..."

One more question, the A sweep is triangular but the B sweep has a flat top
and becoming almost square, that doesn't look right?

I can't access B sweep without taking the case off so I don't know the exact shape but it should look similar to A sweep. A sweep maxes out at 10ns/div, B sweep can go 2ns/div (then there is a 2x multiplier in horizontal amp for 1ns/div) so the ramp is faster on B-sweep at 5/2/1n. Expected waveform is about 1V per time division. If you are sure of the measurement setup this could be the problem.

Is my understanding correct: In 5ns/div with "B horizontal mode" you see a good B sweep but with "A horizontal mode" setting B sweep at R1322 looks distorted?

Were you able to look at A-gate/A sweep/B-gate signals and compare with the picture I sent?

Ozan

EDIT: U9028 should be U902A/B
Dave

I can see -3.6 when 521 is selected, -3. 7 when B is selected and -5.3 when
there is A selected and outside of the 521 range

These look fine. Logic selects B sweep is selected in 5/2/1n mode. I was hoping this would be it but no smoking gun yet.
Ozan

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?

The other thing I'm struggling with is why negative feedback lowers
noise in an amplifier. That's actually an effect that's relevant to
the work we're doing (it's some maths code stuff) and I just don't
know how to explain it. What's the best way you can explain how this
works?

Thanks

Back to 3T77A tunnel diodes :)

It took six full weeks (Feb. 11 order, until today Mar. 22), between the Russian and the US postal services, but I finally got a "Pellet" 1I308J (20 ma Ge TD). It switches right around 20 ma, too!

So even though my 3T77A does trigger reasonably well (as you've seen in my pulser pics, 5 ns pulse at 0.5 MHz rep rate), it won't do a clean display a sine wave above 620 MHz as I previously posted. Rather than leave well enough alone, I'm going to change the 10 ma leaded TD I installed for D42 (trigger regenerator) for the spec'ed 20 ma, and put the original bias fixed resistor back to stock too.
I think it will fit in the clip for the original package (it's quite small) although I may need to bend the top spring clip a little.

More later.

One more question, the A sweep is triangular but the B sweep has a flat top
and becoming almost square, that doesn't look right?

On Mon, 22 Mar 2021, 17:50 Ondrej Pavelka, <info@...>
wrote:

I can see I haven't read your question correctly.

I can see -3.6 when 521 is selected, -3. 7 when B is selected and -5.3
when there is A selected and outside of the 521 range



On Mon, 22 Mar 2021, 17:34 Ondrej Pavelka, <info@...>
wrote:

-3.7 vs -5.3 when I switch between 10 and 5

On Mon, 22 Mar 2021, 16:06 Ozan, <ozan_g@...> wrote:

I think the problem is in horizontal amplifier because I can see nice A
sweep on R1307 and nice B sweep on R1322 coming in and what comes out
(TP1364) is rubbish. Whatever is switching between the two is not

working
Signal at TP1335 is responsible for A vs B sweep.

well. I can see the horizontal position just changing the shape of the
pulse but I think in correct operation this should just be moving the

pulse

but not change its shape drastically.

You observed that B sweep works in 5/2/1n mode (is my memory correct?).
B sweep is used in 5/2/1n settings even in A mode and as far as I can tell
sheet <11> doesn't know whether you are in A or B sweep other than the
control signal coming in from connector N4. In sheet <12> N4 is expected to
be -3V in B sweep and 5/2/1n mode. What voltage do you see at N4 when you
are in B sweep vs A sweep 5/2/1n?

Ozan

OK I replaced Q913 and Q923 and I'm using an external supply of 45V

I have isolated W984, W987, W989, W972, and W991

W972 reads 35V

W984 reads 95V

W987 reads 8.5V

W989 reads -8.5

but W991 is showing 11V

I suspected Q921 but it seems to be OK.

I guess the next suspect is the LM358 in U9028 ???

The inverter stage seems to be working OK but I'm mystified by the 5V rail at 11V !!

Any suggestions welcome.
Dave

If it works like the FG 502 (making an assumption) that is the heart of the unit everything is derived from the triangle wave. If there is any setting where the triangle wave is not running that is why there is no signal. Even the sign is shaped from the triangle wave with a shaper network.

Eric

I would definitely keep the original GR connectors, and if you need to, use an SMA adapter. They're made by GR too and it doesn't have any effect that I can see on my ~ 650 ps (so far) avalanche pulser output. BNC seem to be a crapshoot (and the faster you shoot, the more crap they introduce!)
;)

Yea that is why I only changed the normal connector as it only has a wire to it. I did not mess with the fast rise and fall either.

Eric

For those who haven’t seen this, this is how the GR874 connectors are mounted directly on the Fast Rise and Fast Fall outputs of the Type 106.

I definitely DO NOT want to mess with that!

/g/TekScopes/photo/261997/1?p=Created,,,50,2,0,0

/g/TekScopes/photo/261997/0?p=Created,,,50,2,0,0

Ken,

I think you are right. This is definitely an early production unit.
Although to me, it looks like it might be a transition unit. The reason being that it does have the screw on the front panel to lock the unit in place. Which is how the mechanism works on the later cases. They might have had some leftover earlier type enclosures, and they decided to use them on some units, even though they were clearly designed for the newer cases.
What startles me is that the case fits perfectly, and has obviously not been cut down or trimmed to fit, in anyway shape or form. The bottom feet look very much original as well. However, there is a small hole on the left side of the unit, when it’s facing the user, that seems to be there to facilitate access to a trim pot control of some sort. But that control is not there; it’s actually off center from that access hole. But maybe it was on even earlier units...?

All this make me think it’s a transition model.

I can see I haven't read your question correctly.

I can see -3.6 when 521 is selected, -3. 7 when B is selected and -5.3 when
there is A selected and outside of the 521 range



On Mon, 22 Mar 2021, 17:34 Ondrej Pavelka, <info@...>
wrote:

-3.7 vs -5.3 when I switch between 10 and 5

On Mon, 22 Mar 2021, 16:06 Ozan, <ozan_g@...> wrote:

I think the problem is in horizontal amplifier because I can see nice A
sweep on R1307 and nice B sweep on R1322 coming in and what comes out
(TP1364) is rubbish. Whatever is switching between the two is not

working
Signal at TP1335 is responsible for A vs B sweep.

well. I can see the horizontal position just changing the shape of the
pulse but I think in correct operation this should just be moving the

pulse

but not change its shape drastically.

You observed that B sweep works in 5/2/1n mode (is my memory correct?). B
sweep is used in 5/2/1n settings even in A mode and as far as I can tell
sheet <11> doesn't know whether you are in A or B sweep other than the
control signal coming in from connector N4. In sheet <12> N4 is expected to
be -3V in B sweep and 5/2/1n mode. What voltage do you see at N4 when you
are in B sweep vs A sweep 5/2/1n?

Ozan