Test Equipment Anonymous (TEA) : Discussion and Group Therapy Thread

[tautech]

I am slipping. I have not bought any TE since last Summer. Shame on me.

Slacker !

$20k's worth purchased yesterday.

Not entirely for yourself, I guess..?

Yup, correct.
Things are getting pretty crazy when the day your previous $20k order turns up you need to order as much again....and still orders for more stuff arrives.

At least there is never a day when you're not handling some piece of TE....dreams are made of such !

[Robert]

I bought another clamp meter. A HEME / ITT Metrix 200P auto ranging 20A 200A AC/DC clamp meter with instant or RMS output in addtion to the LCD. Also Voltage, Real and Apparent Power, Powerfactor and frequency. Came with case instruction and 3 Phase adaptor for less than £25 including post. Condition is as new. I've already got one onf these and a 2000P (200 /2000A version) Thery are thery nice but apparently unrecognised meters. Been a few of both the HEME and ITT branded ones on UK ebay recently. I mostly resisted...
https://www.ebay.co.uk/itm/389691090478? I really don't need another 2000A clamp or another of these.

Robert.

[bd139]

Quick holiday report ... quite technology focused this one. That and some GDR weirdness.

Spent a week in Berlin and Dresden hitting museums with a friend. Oh and bars. I will avoid talking about those.

I can't be arsed to write it all up but it's worth noting a couple of high points:

1. Dresden technology museum, Dresden. Really excellent. Old Pentacon / Praktica factory. Full of really unique exhibits of microelectronics, photography and Robotron kit. There was a lot of old fab gear in there and demonstrations - build your own silicon stackup for kids.

2. Amble around Dresden. Still loads of old GDR murals and buildings up there.

3. DDR Museum, Berlin. Excellent view of the GDR and lots of interactive things including "how socialist are you". Not very apparently.

4. Stasi Museum, Berlin. Again excellent although I walked into it with a Praktica MTL50 hanging off me and found out that it was the preferred camera of the era for their operatives. That'd explain the funny looks. Sipped Fanta while relaxing in their meeting room.

5. East Side Gallery, Berlin. Exceptional. That's about all I can say.

Some selected photos all shot on iPhone as I don't have the film dev'ed off the camera I had with me (authentic GDR made Praktica)...

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[bd139]

Oh and a low point. We found this museum...

e4391ed1-af0c-4023-92d5-5ba445e04e8f.jpg

----

Next trip is in 19 days... off to Naples with the youngest two for a couple of days.

[MED6753]

If I ever get the opportunity to travel to Europe again Deutschland will be number 1 destination.

[25 CPS]

Holy crow. I'm still around. I've been so swamped lately that I haven't even been lurking though.

2025 finished up hectic but ok for the most part. Apart from a ton of work and indoor football starting up in late fall, I had two short road trips to the US to visit friends which were both good although the second one got off to a bit of a rough start. The part time security job I have kept trying to call me in, and when I got to the border, I got absolutely reamed out about the portable toolkit in the trunk of the car which always stays in the car in case I have car trouble.

Things started to go bad towards the end of the year. I was stopped at a traffic light on Boxing Day. It was a green Christmas but there was a snowstorm overnight into December 26th and the roads still hadn't been plowed by mid afternoon, and someone changed lanes behind me and then couldn't stop in time and rear ended me at low speed. It was a thud that shook both vehicles and luckily there was no damage. My dash cam's collision detection didn't get set off, so apparently I've been over potholes that were worse than this.

2026 though. I hope it improves from here. I ended up with a serious ankle injury while I was playing football that still hasn't fully recovered. Somewhere along the way, I also chipped a tooth but it was unrelated. Then, one morning while I was entering the parking garage at the train station on my way to work, some jerk driving the wrong way around a corner through the one way entrance sideswiped me and took off. Unfortunately, this time, there was damage but it isn't too bad. Of course, there weren't any cameras in the garage and because he was coming around a corner and he turned into the side of my car, the dashcam got a good side view of his pickup truck but not the front or rear and so no license plate. And then my parents. I don't even know what to say about my parents. They arranged this family meeting dressed up as a social family dinner and then dropped a bombshell on my sister and I that I'm still struggling to comprehend.

That mess with my parents happened right before my vacation started last week. A couple of days after that, I had a road trip for a railway museum conference that I booked last year which was really enjoyable. I needed that break badly and I didn't want to come home. The inured ankle is slowly but surely recovering. I'm still on vacation right now and recovering from the whole overall package the last few months has thrown at me.

Bench time has been pretty much impossible to get between work and everything else going on, and was outright impossible while the ankle was at its worst because of being unable to do the basement stairs. Test equipment hasn't been a total desert though: I did pick up a Hewlett-Packard 3400A voltmeter last week before the railway museum conference.

It's good to be back. Here's hoping I can stay without being thrown off by any more garbage being thrown my way.

[tggzzz]

Welcome back.

I'm sorry to hear there have been a succession of "it never rains but it pours moments"; we can all sympathise. Sometimes life is plodding along quietly, there's a big bang, and then it takes time to settle into "the new normal".

I hope you can find some distracting (relative) normality here.

As for TE, I'm somewhat apprehensive of the approaching radio rally season. I haven't repaired my existing pile, and it looks like my second-hand PVR needs recapping.

[25 CPS]

Welcome back.

I'm sorry to hear there have been a succession of "it never rains but it pours moments"; we can all sympathise. Sometimes life is plodding along quietly, there's a big bang, and then it takes time to settle into "the new normal".

I hope you can find some distracting (relative) normality here.

I've been slowly getting things back to normal but it hasn't been easy. The months-long pummelling of issue after issue has been exhausting. At this point, I'm just looking forward to spring and not being cooped up inside and hopefully things settle down and it's possible to go back to living life instead of tap dancing around the latest mess even though the whole separate set of issues with my parents is going to take a long time to run its course.

As for TE, I'm somewhat apprehensive of the approaching radio rally season. I haven't repaired my existing pile, and it looks like my second-hand PVR needs recapping.

I've got a project backlog too so I've been deliberate about not adding to it. Right now my bench looks unchanged from the fall when things got hectic before the wheels completely fell off in early 2026 with the Hewlett Packard 211AR square still sitting disassembled and the parts I bought for that waiting to be installed. I did briefly get on the bench about 10 days ago to replace the batteries in my Agilent U1272A that's my main portable troubleshooting multimeter which ran out in use, it got substituted with my U1242A to finish the job, so I could get the 1272A back into service.

I totally forgot to mention that I picked up a Fluke 12 multimeter a few days before I got the Hewlett Packard 3400A. Both were available locally and reasonably priced and in working condition so I jumped on those. The standard form factor for handheld DMMs is pretty much settled on a big function/range selection knob below the display and above the input jacks but Fluke tried out a number of other designs like the 12 with a couple of buttons and a switch or the side-switch drawbar meters like the 8060A and others, and I wanted a Fluke 12 to add to my little collection of non-standard form factor Fluke multimeters.

The Hewlett Packard 3400A is another meter that's been on my want list for a long time and two of these came up locally right around the same time and for the same price. One of them was damaged severely and had a rotting meter face and the other was in good condition and was a newer revision that had a standard IEC detachable power cord socket instead of the dreaded PH-163 power connector that comes up so often. It took a few tries for the seller and I to get things lined up but we eventually met and I was able to pick it up a couple of days before heading off to the railway museum conference. The other 3400A in really sad condition is still for sale and that one is old enough that it's got the PH-163 power socket. Of course, no power cord is included. That seller has an HP 8551B spectrum analyzer with the matching 851B display unit but they also look like they're in sad shape and appear to be missing the interconnect cables unless they're not shown in the pictures of either unit's listing.

Speaking of pictures, I should grab some pictures of the Fluke 12 and HP 3400A and post those.

[EC8010]

I have a Fluke 12 and an HP 3400A (with IEC guzzinter). They don't get used very often and I don't much like the operation of the Fluke but I probably wouldn't like to part with them.

[Zenith]

I have 3 and a half HP3400As. All have the IEC connector. They all have the photo chopper and nuvistor input stage. I believe there were production mods to replace the nuvistor with a FET input stage and the photo chopper with an IC chopper amp.

Three work nicely and agree. The other, I can't quite decide whether it's a parts mule or restorable. The meter has a flaking scale - which is a common problem with HP meters of that period, and the photo chopper has a fault. The photo chopper using two neons was ingenious. In time the neons blacken and the striking voltage rises. The LDRs were special and are completely unobtainable.

I've never seen an HP3400B, which was a later version.

I also have a Solartron VM1484. It works on the same principle of matched thermocouples, which I recall was a Western Electric patent. It agrees with the working 3400As.

Then there's a Ballantine 323, which I posted a report of on here. That relies on a pair of unusual diodes. They are referred to as back diodes and uni-channel tunnel diodes. It also has a very odd non-linear meter movement. I'm not satisfied I understand exactly how it works. It agrees with the 3400As and the DSOs.

[tggzzz]

The other, I can't quite decide whether it's a parts mule or restorable.

Or a Newbury hamfest special

[mnementh]

mnem
that is all.

[EC8010]

I've always wondered why people went to the trouble of making true RMS meters. The only genuine application I can see is for measuring noise. But the meter needs enough bandwidth, so that disqualifies most handheld DMMs even for audio, let alone video. Seems to me that true RMS is more of a marketing thing than a genuine need. Perhaps someone can tell me why I'm wrong?

[tggzzz]

I've always wondered why people went to the trouble of making true RMS meters. The only genuine application I can see is for measuring noise. But the meter needs enough bandwidth, so that disqualifies most handheld DMMs even for audio, let alone video. Seems to me that true RMS is more of a marketing thing than a genuine need. Perhaps someone can tell me why I'm wrong?

Presumably non-sinusoidal waveforms, e.g. UK mains - which is visibly non-sinusoidal

Alternatively just use an analogue CRT scope...

With the tangential method the noise signal is connected to both channels of a dual-channel scope used in the alternate-sweep mode.
(a) The offset voltage is adjusted until the traces just merge.
(b) The noise signal is then removed. The difference in the noise-free traces is twice the RMS noise voltage.
(c) This is repeated at a different intensity to show that the method is independent of intensity.
(d, e, f) Scope settings are: horizontal = 500 ms/cm, vertical = 20 mV/cm.
https://bestengineeringprojects.com/ele ... technique/

[Zenith]

True RMS meters were preferred for THD measurements as they dealt accurately with noise as well as the mainly harmonic residual. Older distortion analysers didn't have them and spent a page in the manual apologising for it.

They are used for accurate measurements with all sorts of power electronics, such as inverters, which don't produce anything like a pure sine wave.

I'd guess most people only want to measure the fairly OK 50/60 Hz sine voltage produced by the mains, or through a transformer. For instance, checking that the heater supply to valves is close enough to 6.3V, or checking what the secondaries of an unlabelled mains transformer are. Older analogue meters had a decibel scale, which was done with a nod to audio work. Audio power meters really ought to have had TRMS meters, but assuming you were measuring with a sine wave, average responding (calibrated to RMS sine) is OK. Back in the day, a TRMS meter was an expensive piece of gear on its own.

These days, the dearer DMMs are TRMS. I'm not sure what the crest factor or frequency limits are. I'd guess that when people are paying over £50 for a meter, they expect it, and with modern electronics, it isn't difficult to do using digital techniques, especially if the frequency limit isn't above audio.

[EC8010]

Good point; measuring THD requires true RMS. I hadn't thought of that one. And yes, if there's noise there, then it's really THD + N and definitely requires an RMS meter. Turning to an inverter, if it produces 240VRMS but not a sine wave (and they generally aren't) then when rectified and smoothed, it's not going to produce the expected voltage. A switcher can probably cope with that. A "linear" supply with transformer followed by linear regulator might not. Either way, I don't see the utility of true RMS for measuring an inverter. Unless, of course, the inverter is going to supply a kettle for your cup of tea. Then, you really do want 240V RMS to get the correct heating effect.

Coming back to just measuring audio levels, we're not interested in measuring the amplitude of distorted waveforms. If we want to know the maximum output of something, we want to know the meximum undistorted output, so an average reading calibrated RMS meter is fine.

I do measure THD + N. Mostly on my full bells and whistles dual domain audio test set, but also on my older mostly analogue test set. I often take the output of the analogue test set's filters to an oscilloscope and measure RMS there (having checked that I have an appropriate sample rate).

It really does seem that true RMS in a DMM is mostly marketing hype to justify a price. Conversely, RMS as an automated measurement on an oscilloscope is extremely useful and is my preferred way of measuring noise (because I can see what's going on and decide whether to believe the number).

And yes, UK mains isn't sinusoidal. Generally has flat tops caused by all the capacitor input supplies loading it.

[EC8010]

I hadn't seen that tangential method before. Mind you, it's a long while since an analogue oscilloscope allowed you to explicitly select alternate sweep (as opposed to chopped). No doubt there are plenty of people here who can quote type numbers of oscilloscopes that would do it...

I have a nasty feeling that the tangential method assumes that the noise is white. That's the other problem with measuring noise. Ideally, you view a frequency spectrum of the noise, allowing the white component and 1/f (or worse) components to be quantified individually.

[tggzzz]

It is a neat trick, provided a percent or two is sufficient.

Any vaguely sensible analogue scope will do, i.e. 2 inputs and sufficient bandwith.

Provided the chopping period is much shorter than the sweep speed, then that ought to work too.

[EC8010]

A percent or two uncertainty is perfectly adequate for noise. You generally go to the trouble of measuring noise in order to make a design decision. So you're not actually going to use the exact device you measured, but others of its ilk. +/-1dB sample variation is quite common, and that's +/-12%, so if your measurement uncertainty is less than a third (+/-4%) it's good enough.

[AVGresponding]

True RMS meters were preferred for THD measurements as they dealt accurately with noise as well as the mainly harmonic residual. Older distortion analysers didn't have them and spent a page in the manual apologising for it.

They are used for accurate measurements with all sorts of power electronics, such as inverters, which don't produce anything like a pure sine wave.

I'd guess most people only want to measure the fairly OK 50/60 Hz sine voltage produced by the mains, or through a transformer. For instance, checking that the heater supply to valves is close enough to 6.3V, or checking what the secondaries of an unlabelled mains transformer are. Older analogue meters had a decibel scale, which was done with a nod to audio work. Audio power meters really ought to have had TRMS meters, but assuming you were measuring with a sine wave, average responding (calibrated to RMS sine) is OK. Back in the day, a TRMS meter was an expensive piece of gear on its own.

These days, the dearer DMMs are TRMS. I'm not sure what the crest factor or frequency limits are. I'd guess that when people are paying over £50 for a meter, they expect it, and with modern electronics, it isn't difficult to do using digital techniques, especially if the frequency limit isn't above audio.

Good quality inverters produce a better sine wave than the mains!

[Zenith]

What about crappy inverters or faulty inverters, and what happens when you are developing a good inverter?

[25 CPS]

I have 3 and a half HP3400As. All have the IEC connector. They all have the photo chopper and nuvistor input stage. I believe there were production mods to replace the nuvistor with a FET input stage and the photo chopper with an IC chopper amp.

Three work nicely and agree. The other, I can't quite decide whether it's a parts mule or restorable. The meter has a flaking scale - which is a common problem with HP meters of that period, and the photo chopper has a fault. The photo chopper using two neons was ingenious. In time the neons blacken and the striking voltage rises. The LDRs were special and are completely unobtainable.

I've never seen an HP3400B, which was a later version.

The other 3400A for sale has a seriously flaking delaminating scale. It honestly looks like water got in it and made the whole thing run. It's still listed for sale too. Trouble with neons as equipment has aged has been a problem with a bunch of Hewlett Packard equipment. The photochoppers and the power supplies in 141T mainframes both come to mind immediately.

I've never seen an HP 3400B either.

There was a full service TV and stereo shop near my parents house called Reid and Campbell and they had a repair department at the back of the part of the store dedicated to selling stereo equipment. The bench was along the back wall of the building and there was a big plate glass window facing the showroom so you could see the two technicians working on customer equipment from behind. The wall behind the bench contained all their test equipment and it was all recessed and each piece had an exact size cutout for the faceplates. I remember seeing at least one HP 3400A type meter in that wall of test equipment behind their bench. Most of it was HP or Sound Technology equipment going from memory. I wish I'd paid more attention to the test equipment they were using but I never had much time to look through that window the few times I was in that store.

[tggzzz]

FYI, if anyone needs neons type (I think) 16L or 3L, send me a PM

[Zenith]

The other 3400A for sale has a seriously flaking delaminating scale. It honestly looks like water got in it and made the whole thing run. It's still listed for sale too.

The lacquer layer starts to flake. I think storage in even a slightly damp place will cause it, rather than just age. There are a couple of ways of dealing with it. I removed the pealing lacquer very carefully, then replaced the lacquer with the stuff in a can used to fix charcoal drawings. You have to make paper masks so as not to spray the scale mirror. The scale markings under the lacquer are about as permanent as dirt and you have to be careful with them. It has to be done with the scale removed so the spray doesn't get into the movement. You also don't want lacquer flakes getting into the movement. Something of a mission.

Another way would be to make a new scale with a computer, (scan it, or use meter scale software, or maybe scan a good scale), print it making sure it's the correct size, and then go through the fiddly business of gluing it in place.

I'd be tempted by the tatty 3400A - for the right price - which wouldn't be much. The spare parts including screws and feet can be useful, not to mention more valuable parts. Wait two or three weeks, then phone and if they still have it, offer him no more than $10.

[Robert]

Real world case of needing a TRMS meter.
Setting up a external amplifier for a servo altimeter. Many years ago I was asked to do a duplicate inspection on one of these that had beeen repaired. I refused as the manual said to use a TRMS meter. Tech said it didn't matter. Turned out the shop didn't have a TRMS meter. So I went home and got my Fluke 8060A. The amplifier failed test when measured with the 8060A. When aligned with the 8060A it failed if you tested it with the non TRMS meter. The amplifiers were tested on a rig without the altimeter. When I looked through the history of the manual they had changed the meter model several times. It started off with a specific, rare and obsolete phase quadrature meter, Changed to a specific VTVM. then a DMM and finally to a TRMS DMM. The signal being measures was a 400Hz sinewave that was chopped up in the amplifier.

Robert.