Test Equipment Anonymous (TEA) group therapy thread

[mnementh]

(Attachment Link)

$74 on Amazon...

mnem
 

if you don't behave yourself, I am going to start drop shipping stuff from my shelves to your place in texas.   

*wibble* 

mnem
"Excelsior, you fathead!"

[tggzzz]

and thanks to another forum member there is an 10811 OCXO

I rescued one of those as a the sole saving grace from an ill-judged PPAuctions purchase. I put it in an eddystone case with a nice low-noise 723 based PSU, as per the manual. Bootiful.

This was from a deceased 5371A apparently. Wonder if it was the same device?

They are indeed rather nice bits of kit. Teardown here: http://www.kerrywong.com/2014/07/01/hp-5350b-ocxo-repair/

Mine was from such an MDA, but the rest of the thing ended up in the tip and as bits of scrap metal to be used as convenient[1].

[1] e.g. in my daughter's luxury ice cream business, which it seems you won't be able to enjoy until she manages to create a "good enough" vegan ice cream.

[mnementh]

Yes indeed. From the overcome side I was thinking externally but that's verging on rocket science. Building wideband matching networks for that stuff; forget it. Added 485 to shopping list Edit: actually removing 485 from shopping list. I don't NEED one. I'd LIKE one but I'm supposed to be downsizing!

Have a look at the schematics I added to my previous post, and then go and wash your mouth out with soap.

While I AGREE with you on all of the above in principle; IRL for most applications the 24xx so far exceeds its spec that it is still serviceable even with that bodge in the frontend, which most experienced users know to avoid engaging except as hybrid amp protection for when they're about to do something stupid. And Tek did make a matching attenuator specifically for use above 100MHz, just like the ones Siglent makes for their scopes and the one I bought with my 1054Z.

You ARE right... it WAS A SIN to put that clusterfuck right there in the frontend of what is otherwise their masterpiece of portable analog scope design. It's just a sin that for the most part, you CAN live with.

mnem
 

The 24x5 spec at 300MHz is that the input impedance is either j35ohms, or 50+j35 ohms =~61ohms. Does lipstick allow a pig to "exceed expectations"?

Can you point to the "matching attenuator specifically for use above 100MHz", please? I'm not aware of any that address the //15pF issue.

That depends; If you're planning to kiss the pig, maybe...

I'm AGREEING WITH YOU. It's a sin. PERIOD.

It still works most of the time; you still get get useful information from what is displayed, and you protect those effing delicate hybrid ICs in the frontend. One of the very first discussions I first read your little diatribe on the subject, another user mentioned the atten complete with part #. Jeebus; it was forever ago...

I've never NEEDED it; I expect the waveform to be flat and skewed whenever 50Ω is engaged and I process the information internally with that in mind. Maybe I'm just not used to everything being spoon-fed to me; I'm used to having to understand my tools and their shortcomings. 

As I said; it's a sin you can LIVE WITH. 

Cheers,

mnem
"In God we trust; all others pay cash."

[mnementh]

Dammitt...

I got up early to get some work done in the garage before The SUCK sets in; cooked breakfast and ate it over the TEA and checking my CL postings, and here it is after 11 o'clock already... 

mnem

[tggzzz]

Yes indeed. From the overcome side I was thinking externally but that's verging on rocket science. Building wideband matching networks for that stuff; forget it. Added 485 to shopping list Edit: actually removing 485 from shopping list. I don't NEED one. I'd LIKE one but I'm supposed to be downsizing!

Have a look at the schematics I added to my previous post, and then go and wash your mouth out with soap.

While I AGREE with you on all of the above in principle; IRL for most applications the 24xx so far exceeds its spec that it is still serviceable even with that bodge in the frontend, which most experienced users know to avoid engaging except as hybrid amp protection for when they're about to do something stupid. And Tek did make a matching attenuator specifically for use above 100MHz, just like the ones Siglent makes for their scopes and the one I bought with my 1054Z.

You ARE right... it WAS A SIN to put that clusterfuck right there in the frontend of what is otherwise their masterpiece of portable analog scope design. It's just a sin that for the most part, you CAN live with.

mnem
 

The 24x5 spec at 300MHz is that the input impedance is either j35ohms, or 50+j35 ohms =~61ohms. Does lipstick allow a pig to "exceed expectations"?

Can you point to the "matching attenuator specifically for use above 100MHz", please? I'm not aware of any that address the //15pF issue.

I'm AGREEING WITH YOU. It's a sin. PERIOD.

It still works most of the time; you still get get useful information from what is displayed, and you protect those effing delicate hybrid ICs in the frontend. One of the very first discussions I first read your little diatribe on the subject, another user mentioned the atten complete with part #. Jeebus; it was forever ago...

I've never NEEDED it; I expect the waveform to be flat and skewed whenever 50Ω is engaged and I process the information internally with that in mind. Maybe I'm just not used to everything being spoon-fed to me; I'm used to having to understand my tools and their shortcomings. 

As I said; it's a sin you can LIVE WITH. 

I understand that we agree it is a "sin" I don't understand the relevance of "...so far exceeds its spec...", but no matter - it is unimportant.

Despite being aware of the problems of the //15pF, I have been caught out. The trace looked strange, but not in a way that was immediately and obviously traceable to the //15pF.

More positively, what did you mean by "...matching attenuator specifically for use above 100MHz"? I'm curious as to what that is and how it helps.

[mnementh]

The relevance of "so far exceeds its spec" is that even with the distortions caused by impedance mismatching, it is still fast enough and sensitive enough to give useful information about the waveform.

The capacitive loading, as with impedance distortion, I think has a lot more to do with how you're used to thinking about what you see on the screen.



I'm used to thinking in terms of this, where the waveform over time is the primary information being presented. The SHAPE is what's important. You are essentially concentrating on the waveform, seeing the display as representation of SHAPE rather than its absolute accuracy.



A lot of people are more used to thinking of the waveform as a graph, plotting datapoints on the screen over time. The ABSOLUTE VALUE of each sample is what's important; usually because there are relatively few of them. You are looking at the output of the scope more as a serial voltmeter in this case.

In short; thinking analog vs digital.

As for the atten; I was referring to something someone else posited in a discussion forever ago; as it was supposedly made by Tek for this instrument, I have no reason to believe it would distort the waveform any more than absolutely necessary, and that the results would be superior than the built-in "50Ω".  I may be completely wrong as far as it correcting the capacitive loading; no idea.

Either way, you can definitely still gain useful information from a 24xx scope with the 50Ω engaged; so while not the BEST solution, it still serves its primary purpose: to protect that delicate frontend.

mnem
*Hopelessly Analog*

[tggzzz]

If that was the only form of distortion,I could live with it.

Unfortunately when you are looking at bursts of bits where the bit rate is sufficiently high that there is Inter-symbol interference due to the probe's dimensions, the cause and effects can be subtle. Yes, a mere 100Mb/s is sufficiently fast

Been bitten by that

[mnementh]

Again... every tool has its limits; they are all bound by their fundamental nature.

Analog is limited by slew rate and the loading the frontend applies to the DUT; digital tends to present much lower loading to the DUT, but is prone to digital artifacting. Part of why most of "the really smart dudes/dudettes" I've ever known always keep a dusty but decent CRO handy to reality-check their shiny DSOs. 

mnem
"So Doc, tell me the bad news."
"Mister D, you are frighteningly fat. I have no idea how you're still alive."
"I don't think I like that answer... I'm going to get a second opinion."
"Okay; you smell funny too."

[BU508A]

Building switching converters has always interested me.

Perhaps you'll find this thing interesting.
Buck-boost converter with single 3.7V input and bipolar (+/- 15V) output@100mA with an LT1172.
I'm looking for a "quiet" converter to supply sensitive opamp circuits so I tested this one.
It is mentioned in the DN47 of LT.

Schematic:



Output, used two LEDs @ 1mA as a load, driven by a constant current source. blue=-15V; red=+15V



The prototype itself:



And this is what my scope sees:

+15V out:



-15V out:



Im not really satisfied, obviously. Need some additional filtering, though.

Edit:
Added DN47

[tggzzz]

Again... every tool has its limits; they are all bound by their fundamental nature.

Analog is limited by slew rate and the loading the frontend applies to the DUT; digital tends to present much lower loading to the DUT, but is prone to digital artifacting. Part of why most of "the really smart dudes/dudettes" I've ever known always keep a dusty but decent CRO handy to reality-check their shiny DSOs. 

mnem
"So Doc, tell me the bad news."
"Mister D, you are frighteningly fat. I have no idea how you're still alive."
"I don't think I like that answer... I'm going to get a second opinion."
"Okay; you smell funny too."

The way I allowed myself to be bitten would have happened with either an analogue or a digitising scope. It was a waveform and probing issue, no more. A simple Spice simulation duplicated my problem.

[mnementh]

Those happen too. That's why your most important tool is always the one right behind your eyes. You proved the problem to yourself using a different method; which is valid engineering. Possibly THE MOST valid form thereof.

mnem
"Absence of proof is not proof of absence."

[bd139]

Building switching converters has always interested me.

Perhaps you'll find this thing interesting.
Buck-boost converter with single 3.7V input and bipolar (+/- 15V) output@100mA with an LT1172.
I'm looking for a "quiet" converter to supply sensitive opamp circuits so I tested this one.
It is mentioned in the DN47 of LT.

Schematic:



Output, used two LEDs @ 1mA as a load, driven by a constant current source. blue=-15V; red=+15V



The prototype itself:



And this is what my scope sees:

+15V out:



-15V out:



Im not really satisfied, obviously. Need some additional filtering, though.

Edit:
Added DN47

That's really cool. Thanks for posting 

I had half of a similar design on the breadboard ages ago but couldn't get the noise spikes down to an acceptable level. Additional filtering as you say. Then I found that the royer converters tend to have a much less noisy output. The converter I built earlier for the +-15V had no harmonics or spikes I could detect with the DS1054Z FFT which was a surprise! Alas it wasn't that efficient and the 2n2219's I was using for switching were getting quite warm. I didn't delve too much further into it as I got distracted by radio things 

Again thanks for posting - that's a really neat build. A fan of the Roth prototype boards as well I see

[mnementh]

Isn't that really the price you have to pay for clean power? You can have efficiency, which switchers give us, or clean, which operating in linear mode gives us. 

Times you really want both is when everything comes up poop. 

mnem
"Tastes like purple."

[bd139]

That was more of an artifact of my shitty engineering that was. Jim Williams designed some nice CCFL inverters for laptops which were crazy efficient. Just requires the right knowledge (and a current probe which I don't own yet  )

[med6753]

Got the Heath V-7A all put back together and fired it up and things immediately went south.  Monitoring the B+ and it would come up to +80V and then promptly drop down to +20V and stay there. No shorts, no smoke. Had me scratching my head for a while but finally found it. Broken wire that grounds one side of the filament and functions as a common reference for the entire VTVM. Without that ground the entire circuit floats like it's lost in space. Once fixed now have 52V B+ which is good. Manual sez +50V to +70V.

But things are still fubar. Real bad fubar. ACV tries to read negative. Pegs meter below 0. DCV reads fine on 1.5V and 15V range. On 5V and 50V range reads way high. Ohms is complete no work. Meter doesn't swing to the right to infinity. Ohms battery is good and it has good contact. I can measure 1.5V at the 9.1 ohm resistor in the start of the ohms divider.

So.....one thing at a time. But I suspect problem with ACV and Ohms is one in the same. I have a softcopy manual but it does NOT have all the pictorials on how the decks should be wired. All I have is the schematic to try to slug thru those switches.   

[mnementh]

That was more of an artifact of my shitty engineering that was. Jim Williams designed some nice CCFL inverters for laptops which were crazy efficient. Just requires the right knowledge (and a current probe which I don't own yet  )

Yeah, but a Royer drives the transistor bases off the transformer; pretty hard to make that not drive linear mode unless you do some waveform-shaping to force it into a proper square wave. As long as you can keep the frequency such that it's not a problem elsewhere... it seems to me the cleanliness of power output is a function of the fact it operates mostly in linear mode...?

I mean, most of the "true-sine-wave" inverters I've seen use a variant with feedback taps at either end of the primary, so that the waveform doesn't chop on one side...

mnem
 

[nixiefreqq]

mnem
"In God we trust; all others pay cash."
[/quote]

when i was 17 a neighbor gave me a 10 year stack of playboys.  pulled out the issues with jean shepherd and gave the rest to my brother.  and yes......read shep BEFORE looking at the naked ladies.  "ludlow kissel and the dago bomb that struck back" still makes me laugh out loud, because it could have happened in my old neighborhood.

[mnementh]

Hear "Ludlow Kissell etc" in Shep's Own Words

mnem
 

[bd139]

Yeah, but a Royer drives the transistor bases off the transformer; pretty hard to make that not drive linear mode unless you do some waveform-shaping to force it into a proper square wave. As long as you can keep the frequency such that it's not a problem elsewhere... it seems to me the cleanliness of power output is a function of the fact it operates mostly in linear mode...?

I mean, most of the "true-sine-wave" inverters I've seen use a variant with feedback taps at either end of the primary, so that the waveform doesn't chop on one side...

Basic royers are very non linear and noisy as hell. It's like someone whacking a tennis ball back and forth. I think as far as they go is generating crud cheaply  . It's only the resonant and Baxandall versions that have any semblance of tasty sines coming out and have any linear drive characteristcs. I was trying the resonant version there and mostly because I didn't have a suitable inductor as the current source for the Baxandall.

[med6753]

(Attachment Link)


Hear "Ludlow Kissell etc" in Shep's Own Words

mnem
 

I can assure you, I am NOT a nerd. 

[BU508A]

Again thanks for posting - that's a really neat build. A fan of the Roth prototype boards as well I see

You're welcome. 

 

Good eye! I'm a fan of them since I've discovered them many many years ago @Reichelt.
They're are of a good quality to a reasonable price imho.

[med6753]

Well gang...big step forward on the Heath V-7A. Found the issue with the ACV and Ohms. As I thought it was same thing. I had the fucking meter wired backwards.  D'OH. 

DCV is also looking better but not perfect. I may have a precision resistor that's gone bye-bye. But at least progress.

[mnementh]

Yeah, but a Royer drives the transistor bases off the transformer; pretty hard to make that not drive linear mode unless you do some waveform-shaping to force it into a proper square wave. As long as you can keep the frequency such that it's not a problem elsewhere... it seems to me the cleanliness of power output is a function of the fact it operates mostly in linear mode...?

I mean, most of the "true-sine-wave" inverters I've seen use a variant with feedback taps at either end of the primary, so that the waveform doesn't chop on one side...

Basic royers are very non linear and noisy as hell. It's like someone whacking a tennis ball back and forth. I think as far as they go is generating crud cheaply  . It's only the resonant and Baxandall versions that have any semblance of tasty sines coming out and have any linear drive characteristcs. I was trying the resonant version there and mostly because I didn't have a suitable inductor as the current source for the Baxandall.

    http://www.sophia-electronica.com/Baxandall_parallel-resonant_Class-D_oscillator1.htm

mnem
I learned something today!

[bd139]

Well gang...big step forward on the Heath V-7A. Found the issue with the ACV and Ohms. As I thought it was same thing. I had the fucking meter wired backwards.  D'OH. 

DCV is also looking better but not perfect. I may have a precision resistor that's gone bye-bye. But at least progress.

Hahahahaha. Been there and done that before 

Again thanks for posting - that's a really neat build. A fan of the Roth prototype boards as well I see

You're welcome. 

 

Good eye! I'm a fan of them since I've discovered them many many years ago @Reichelt.
They're are of a good quality to a reasonable price imho.

I recognised the colour . Yeah they're excellent boards. I use the stripboard they sell occasionally (yes I still use stripboard  ) as it's fun trying to get dense layouts out of it. Here's one I did a couple of years back. It's a 3 pole high Q bandpass filter.

[mnementh]

Well gang...big step forward on the Heath V-7A. Found the issue with the ACV and Ohms. As I thought it was same thing. I had the fucking meter wired backwards. D'OH. 

Well, at least this PEBWAC error wasn't accompanied by smoke and a shower of sparks... 

mnem
"Every silver lining has its dark cloud."