Test Equipment Anonymous (TEA) group therapy thread

[Swake]

This thing is on sale on Ebay and I must say that for a seemingly simple multimeter it seriously confuses me on how to connect the wires.

Is the bottom left black connector the common for DC? And the yellow one for AC? In that case how should the left switch be used and why is there a AC sign on the right of the yellow Volt connectors, while I would expect to be able to measure DC volts too or is the AC sign only for the 250 and 500 ranges? Why is there a bridge over the Rx10, and what does it change if this thing is removed. What does R.P. stand for? Is that the common for the resistance measurement or the first range? I think 5V DC is not a common value back in the time, is that an input to power the Ohms range? What is N.F. supposed to be.   

[Messtechniker]

N.F. (German: NiederFrequenz) might be low frequency so that the decibel scale applies.

[W6EL]

Oh, and my HP-3490A arrived. After it blew out a RIFA cap (flames like a torch, loud noise, awful smell, you know it), it's working fine. I am considering adding a true RMS circuit of some kind or another inside it, because.. why have a 6 digit meter without actually reading RMS... We can do this, it's 2023, there's dozens of ways to measure RMS and it'll be fun to experiment. This thing has the most satisfying switches and rolling unit selector you've ever felt. Click!

The earlier HP 3480 series with 3484A plug-in, did have a TRMS option (043), based on similar thermocouple to the 3403 series, strange they never offered this option for the 3490A. 

David

Hi David,

Indeed that does seem odd.

What does the group think about the LTC1968 for RMS conversion?

I think the requirements here for my RMS modification to the HP3490A would be that we have several MHz of bandwidth available and that the converter accept the output of the attenuator, which is supposedly 0 to 1 volt, possibly over of course. This is of course difficult territory for many devices. Or should I put the circuit in another place?

--E

[Robert763]

Choice of RMS converter depends on your requirements.
The LTC1968 is easy to use, has good linearity and reasonable crest factor (up to 4) and frequencies upt to 100's kHz,
The AD 536 has poorer linearity but better crest factor (7) and higher frequency.
The AD 637 is the best of the bunch but at a premium price. Same linearity as LTC1968, crest factor to 10 and frequency to 8 MHz.

[W6EL]

Hi Robert,

The AD637 has bandwidth to 8 MHz if you're ok with a 3dB error, which I am not really. 3dB is significant. The 1% error bandwidth is 200 KHz. Still not too bad.

The LTC1968 has 1% error bandwidth of 500 KHz. About 6 Mhz if you can go out to 10% error. (The plot is on page 5 of the datasheet, bottom-center).

I like that the AD637 has a log output available, that might be a nice thing to try. And I do see the higher crest factor, which is just wonderful at +/- 1% error at CF=10.

With regards to the complexity of implementation, I see that the AD637 requires two capacitors and optionally a high-precision trimmer. That doesn't seem too bad. I don't need the additional steps for the below-10Hz measurements. It looks like the LTC1968 needs a cap for AC coupling and then it is recommended to go into a "CAVG" capacitor to smooth out the readings. I believe the integration mechanism of the HP 3490 will basically take care of the averaging for the selected integration period.

That puts these two options pretty close in terms of complexity. I think. Looks like the AD637 seems to anticipate a +/- supply, and that may be a good thing for low-level signals anyway.

I'm leaning towards the AD637 simply because I think my realistic requirements are not several MHz. The kinds of non-sine signals I'd measure are usually a lot lower.

Then there is also the LT1088, but I don't know if I'm up for adding that many parts

[Black Phoenix]

Well probably my first post here about my own equipment:

After 5 long years, my Fluke 289 is back, after being in Portugal waiting for transport. He met the 87V who was bought in 2019 as a "need a DMM right now and mine is 10000KM away"! Although some days ago I sold my Fluke 54-II for an offer who was hard to refuse. I didn't want it but truth to be told the last time I really used it in a important task was back in 2014...

It's good to have then back (together with a ton more stuff that I could carry with me).



The probe bags are left the TLK-225 kit but I removed the TwistGuard TP-175 probes for the TP-220 Industrial probes. The other small one is just the TL-224 leads, TP-220 Industrial probes, AC285 Alligator clips and AC220 Pincer clips in the pouch of the Fluke Electronics kit that I found being sold empty online.

Also not present is the Fluke 225 Scopemeter who was sold way back in 2016 when my contract finished in the Telecom company and I gone through some unexpected health expenses. That I solely regret doing it because:

First - it didn't turn my life into something better by selling it and getting the money (the health problems still continue here, not life treating ones) and;
Second - I had to refuse some freelance industrial maintenance work to old customers I worked for while employed because of not having it with me any more.

[Ice-Tea]

Huecke TV-Demodulator 327. Popped something in the PSU when powering up. Not sure if it's a RIFA, smells a bit less "papery". Free for anyone that wants it (shipping to be payed, though).

EDIT: manual included.

[Runco990]

You know... I LOVE old test equipment.  My lab, an entire bedroom, is full of old HP and Tektronix gear, all lovingly restored and weighs a ton.  And then there's the garage......   

But I am even more blown away with what we can get TODAY!  Like the tiny SA, pocket scopes, etc..  It is absolutely AMAZING that you can theoretically have a full lab setup with room to spare in a CLOSET! 

Just incredible.  And yet, I can't seem to part with my vintage gear..... 

This is my current lab.  What you DON'T see are the 12 other scopes, 2 more HP spectrum analyzers, etc, etc, etc.  It's an illness.   
It was NOT fun to move it all into this new house.  Turns out I own way more T.E. than furniture....

[TERRA Operative]

I like your setup. 

[wkb]

I care rats ass about what they say about their glorious newfangled NanoVNA toys and whatnot: using the T&M of old produced by the likes of HP, R&S, Marconi, Tektronix etc etc simply gives one that "wow" factor that is basically 'unexplainable' to those who lack the necessary genes.

I just feel sorry for them 

[Neomys Sapiens]

I'm leaning towards the AD637 simply because I think my realistic requirements are not several MHz. The kinds of non-sine signals I'd measure are usually a lot lower.

Then there is also the LT1088, but I don't know if I'm up for adding that many parts

The AD536 seems to have spawned an improved version in the guise of the AD736 /AD737.
All of them except the LTC1986 are at least available in one hermetic case, some even more than one. The LTC1986 is only available in MSOP. I am curious how stable that can be.

[Runco990]

I like your setup. 

Thank you!  It still needs some tweaking, but it's nice and cozy when it snows outside!   
My old shop, while quite big and well set up, was in a cold garage....  not always fun.

[Runco990]

And to share some TEA, I just got this RCA power meter and recently this Lafayette FET meter.
So the Lafayette was the usual ebay "not tested" which means "tested and known broken".  It had 2 fried resistors and an open pot.  I took it completely apart, drowned it in the ultrasound tank, cleaned, fixed and it works a treat.  I bought it entirely because it looked cool, and I like the "0" feature for aligning FM discriminators.  Of course, I needed another meter like a hole in the head.

The RCA was the proper ebay "landfill-to-you" pick.
It looked terrible.... movement was OBVIOUSLY out of whack, it was VERY yellow and cloudy and scratched AND... the cord was cut, so you KNOW it came from a "working environment".

Long story short, it must have fallen and instead of someone fixing the movement, why not just solder another resistor in there to barely get a reading at 120v but no where else?  Nope. 
So I undid all that, fixed the movement and polished the meter plastic.  I may re-paint the hammer tone case one day.  But for now it calibrates and works.  Did I need it?  Hell no!  Did I want it for $14?  Yep.   
I'll find a permanent spot on the bench for it.

[med6753]

You know... I LOVE old test equipment.  My lab, an entire bedroom, is full of old HP and Tektronix gear, all lovingly restored and weighs a ton.  And then there's the garage......   

But I am even more blown away with what we can get TODAY!  Like the tiny SA, pocket scopes, etc..  It is absolutely AMAZING that you can theoretically have a full lab setup with room to spare in a CLOSET! 

Just incredible.  And yet, I can't seem to part with my vintage gear..... 

This is my current lab.  What you DON'T see are the 12 other scopes, 2 more HP spectrum analyzers, etc, etc, etc.  It's an illness.   
It was NOT fun to move it all into this new house.  Turns out I own way more T.E. than furniture....

And I thought I had too much TE. This is my current lab in a spare bedroom just as yours. I moved it all in April to this current location and it took me 2 months to get it all set up. And yes, love the vintage stuff.






Currently restoring a Tek Type 516.

[Runco990]

LOVE the tube scopes, but I just don't have room for them.  I do have one of those tiny RCA one's though.

But I think Paul Carlson has us all beat when it comes to the sheer tonnage of test equipment! 

Maybe if I had a bigger house.... 

[TERRA Operative]

Just recieved delivery of a Tek SG5030 levelled sinewave generator. No levelling head of course, but I didn't buy it for that.
My existing unit is playing games so this one will make it easier to repair, or just use this one anyway..

I fired it up and besides the expected 'requires calibration' and 'calibration constants are borked!' errors which were mostly bypassed with a reinitialization of the internal memory, there was a huge list of errors about all sorts of output parameters... yay.

I took the top off and checked the internal coax connections for fun, compared to my existing unit (it was obvious someone was inside before me) and, oh, look at that, the two coax cables to the output amplifier board are reversed..... lol. I seem to have a memory of the manual having some of the internal connections labelled wrong (double lol), or was that something else I am thinking of?

I correct those connections, and now there are no errors (besides the one telling me to calibrate).

Most importantly, there are no 'output unlevelled' errors like my existing unit.

Tonight I'll give it a good going over, adjustment/calibration and replace the Dallas NVRAM chips with FRAM's.
Then, time to mix and match the best of both to get a nice working unit, then the left overs will be repaired into another unit for sale, once I repair my old levelling head (with broken internal PCB).

And then it's back to adjusting and calibrating my scopes for sale. (Except Vince's reserved one haha ).

[W6EL]

LOVE the tube scopes, but I just don't have room for them.  I do have one of those tiny RCA one's though.

But I think Paul Carlson has us all beat when it comes to the sheer tonnage of test equipment! 

Maybe if I had a bigger house....

The tube scopes, especially the all-tube ones, are really something. Just outright works of art. I believe I had a Tek 545 when I was little (8 years old, long story). It was just such a fascinating machine to me, and I would often get lost in all the functions and end up with a little dot in the middle and have to ask my dad to come reset it. The insides were amazing. The swing-out board on the right side with a dozen or so vacuum tubes, each perfectly wired to large ceramic terminal strips... it's really something. But it is hard to keep them going. Not from the tubes but from all the capacitors and bad switches.

I still have my Tektronix 465 and 475. The 475 is connected to my HF station so that I can monitor my transmit signal. No analog meter is anywhere near as truthful as an analog oscilloscope when it comes to measuring moving power. As for my 465, the tube does not come on. Something is wrong with the high voltage inverter, and I'm just not up for fixing it. I got the HV probe and all so that I could do this work, but I feel like there's too much at risk digging around in that section. So, it sits. Anyone want to fix it for me? 

I'm using my digital HP 54645D+FFT right now for most things, and I have to say, it's a nice scope. HP made some annoying scopes for sure but this one is more than tolerable and is just filled with convenience features. The menus are short and to the point, buttons on the panel do what you expect. I can't complain. It's responsive too.

I also had a LeCroy 7200A (not the "wavepro" 7200A model, but rather, the old school clunky i386 one) which was purely a waste of time. What a nasty scope. I actually gave it away. I told the guy I'd charge him if he brought it back. Early digital scopes are sometimes really awful and this one really was. Terrible clumsy non-responsive UI filled with menus and complexity nobody needed. Impossible to just turn it on and go. Sophisticated, works out to 2 GHz with the right probe adapters (two channels used in a kind of ping-poing fashion at 6 bits resolution), color VGA screen, has its own interactive BASIC interpreter, but just a nasty scope. A true PITA and I wish I could get the time I spent with it back. Here's some photos from way back when I had that clunker.

Anyway! Yes, old gear is better even if it isn't.

[tggzzz]

I still have my Tektronix 465 and 475. The 475 is connected to my HF station so that I can monitor my transmit signal. No analog meter is anywhere near as truthful as an analog oscilloscope when it comes to measuring moving power.

I'm not sure what you mean by "moving power", but a scope's vertical spec is 2%. That will also be frequency dependent because of the scope's frequency response and its VSWR of 1.3 (IIRC) i.e. >2dB.

OTOH an HP432 + 8474 thermistor mount is (nominally!) metrology grade: the calibration tewaks for different frequencies run from 100% to 88%, i.e. 0.5dB max. And it works to many many GHz CW only, of course, and it will also be measuring the harmonics that are probably invisible on a scope.

Can I interest you in mine; it is on fleabay

[vk6zgo]

I still have my Tektronix 465 and 475. The 475 is connected to my HF station so that I can monitor my transmit signal. No analog meter is anywhere near as truthful as an analog oscilloscope when it comes to measuring moving power.

I'm not sure what you mean by "moving power", but a scope's vertical spec is 2%. That will also be frequency dependent because of the scope's frequency response and its VSWR of 1.3 (IIRC) i.e. >2dB.

OTOH an HP432 + 8474 thermistor mount is (nominally!) metrology grade: the calibration tewaks for different frequencies run from 100% to 88%, i.e. 0.5dB max. And it works to many many GHz CW only, of course, and it will also be measuring the harmonics that are probably invisible on a scope.

Can I interest you in mine; it is on fleabay

HF comms radio is normally quite narrowband, so 'scope bandwidth of a 475 may be neglected.

An oscilloscope is not normally used standalone as a power meter but would be normally set up to a convenient scale so that changes in the output power would be visible.

An analog 'scope effectively has no inertia, compared with an old-style meter movement, which has inherent errors related to the ballistics of the movement.

Many years back, at my old job, we received a Modulation monitor from a remote AM station, which allegedly was reading high, with the mod scale "twanging".

We sent another off, & proceeded to test the "faulty" one, which was found to be normal, just in time for a report from the "first in" maintenance people that the replacement was also faulty.

The Boss sent two of us off in a van to check.

Arriving at the site, the Mod Mon was happily twanging away.
Grabbing an analog 'scope, the problem was immediately obvious, with the RF signal being driven to cutoff due to excessive modulation.

The MM showed little sign of distress other than the meter "twanging", nor was the audio audibly distorted.

It turned out that the "first in" guys had "lined" the TX mod up using an 8dB lower audio level than the correct one.

[W6EL]

I still have my Tektronix 465 and 475. The 475 is connected to my HF station so that I can monitor my transmit signal. No analog meter is anywhere near as truthful as an analog oscilloscope when it comes to measuring moving power.

I'm not sure what you mean by "moving power", but a scope's vertical spec is 2%. That will also be frequency dependent because of the scope's frequency response and its VSWR of 1.3 (IIRC) i.e. >2dB.

OTOH an HP432 + 8474 thermistor mount is (nominally!) metrology grade: the calibration tewaks for different frequencies run from 100% to 88%, i.e. 0.5dB max. And it works to many many GHz CW only, of course, and it will also be measuring the harmonics that are probably invisible on a scope.

Can I interest you in mine; it is on fleabay

The issue is similar to what vk6zgo pointed out.

With a meter, you cannot see the waveform. You can't tell if the modulation is flat-topping, and you can't see the carrier from the modulation. When I speak normally, even with a speech compressor on, I do not see much movement on my normal analog watt meter. It's like an extremely low-pass filtered version of my speech. Some people modify meters with "PEP kits" to read out the PEP level, but in doing so, they sacrifice responsivity since the meter must "charge and hold". With a scope, especially a fast analog one, you get all of this. You get very fast response, and you can see the modulation clearly. You can tell right away if you're flattopping. You can see the carrier and observe how the modulation depresses and boosts the level.

This is *especially* so on AM. Many meters just fall flat on their faces when faced with AM modulation. The move down or hardly at all, depending on how the rectification was done at the meter. And if you ask me, it's just not worth screwing around with. Use the meter for unmodulated carrier readings. Use a scope when there is modulation.

vk6zgo: Was the AM station running +4dBu or +8? Did the first in guys cal it 0dBu...? It's great that the equipment handled it as gracefully as it did though!

[tggzzz]

I still have my Tektronix 465 and 475. The 475 is connected to my HF station so that I can monitor my transmit signal. No analog meter is anywhere near as truthful as an analog oscilloscope when it comes to measuring moving power.

I'm not sure what you mean by "moving power", but a scope's vertical spec is 2%. That will also be frequency dependent because of the scope's frequency response and its VSWR of 1.3 (IIRC) i.e. >2dB.

OTOH an HP432 + 8474 thermistor mount is (nominally!) metrology grade: the calibration tewaks for different frequencies run from 100% to 88%, i.e. 0.5dB max. And it works to many many GHz CW only, of course, and it will also be measuring the harmonics that are probably invisible on a scope.

Can I interest you in mine; it is on fleabay

The issue is similar to what vk6zgo pointed out.

With a meter, you cannot see the waveform. You can't tell if the modulation is flat-topping, and you can't see the carrier from the modulation. When I speak normally, even with a speech compressor on, I do not see much movement on my normal analog watt meter. It's like an extremely low-pass filtered version of my speech. Some people modify meters with "PEP kits" to read out the PEP level, but in doing so, they sacrifice responsivity since the meter must "charge and hold". With a scope, especially a fast analog one, you get all of this. You get very fast response, and you can see the modulation clearly. You can tell right away if you're flattopping. You can see the carrier and observe how the modulation depresses and boosts the level.

This is *especially* so on AM. Many meters just fall flat on their faces when faced with AM modulation. The move down or hardly at all, depending on how the rectification was done at the meter. And if you ask me, it's just not worth screwing around with. Use the meter for unmodulated carrier readings. Use a scope when there is modulation.

vk6zgo: Was the AM station running +4dBu or +8? Did the first in guys cal it 0dBu...? It's great that the equipment handled it as gracefully as it did though!

By the time you can see anything much on a scope, the tx will already be significantly overdriven (for AM) and splattering harmonics out of band. I'd have thought an SDR or SA would be a more sensitive test.

[Robert763]

LOVE the tube scopes, but I just don't have room for them.  I do have one of those tiny RCA one's though.
<SNIP>

I'm using my digital HP 54645D+FFT right now for most things, and I have to say, it's a nice scope. HP made some annoying scopes for sure but this one is more than tolerable and is just filled with convenience features. The menus are short and to the point, buttons on the panel do what you expect. I can't complain. It's responsive too.

<SNIP>

If I was allowed to keep only one of my 'scopes it would be my HP 54645D with measurement module. Yes I have "better" 'scopes but the little HP is a good all-rounder and, for someone brought up on analog 'scopes, so nice to use. Having a separate processor for the user interface make such a difference to the responsiveness.


Anyway! Yes, old gear is better even if it isn't.

[EggertEnjoyer123]

Here's the HP comb generator teardown, as promised. I bought it for $20 at the swap meet last weekend.
I had to replace the original power connector, as it was the obselete 163 connector. I just cut a power cable and replaced the connector with the plug. The N connector on the front was also busted (the center pin was corroded and half of it was missing), so I replaced it with a few connectors I had lying around. The N connector was part of a 10dB attenuator, but my current setup just passes the signal through without any attenuation. Everything still seems to work.
There is a resonance at 11.5 GHz, but the old connector also had that issue.

[W6EL]

By the time you can see anything much on a scope, the tx will already be significantly overdriven (for AM) and splattering harmonics out of band. I'd have thought an SDR or SA would be a more sensitive test.

Well, I respectfully disagree. If you know what the modulation is supposed to look like, you can definitely see it right away.

I'm usually the first person to say "Use a spectrum analyzer, not a scope" for RF, but in the case of modulation with a relatively low data rate, a scope is very appropriate. Modern scopes actually can pull this off in the time domain too, but none that I own!

Here is a "textbook example" from a 1970s ARRL handbook.

[Robert763]

Got a package today:
Well packed for a change and very heavy
A ebay purchase but what is it? Not really TE but somewhat related.

Robert.