Test Equipment Anonymous (TEA) group therapy thread

[Vince]

SURPRISE !!!


Found this beauty on leboncoin.fr for only 50 Euros.... 6 weeks later the deal is finally done and I received it today 

A Rochar A.1335 Neeksee DVM

I know, I know.... I already have two of these.... but, I love them, and they are very, very sick and I am struggling to fix them.
So I though having a third one for spares or to take measurements, couldn't be a bad thing eh...
Plus, this one is the luxurious version of this meter, i.e. it's got auto-ranging and can do AC as well as DC.
The base model is manual ranging and can only do DC.

Just unpacked it and fired it up a moment ago to see what I have got...
Physically and cosmetically it's in good nick. Needs a good cleaning of course, that goes without saying...
Electrically, it doesn't work "obviously", but it's plenty alive.
It powers up, the display tubes are working and bright bar the second from the right, which shows no sign of life whatsoever...
It also fails to count / measure anything.
At power up, display shows random digits.
However as soon as I fiddle with the triggering switch and push-button, it immediately resets / clears the display. So at least we know the reset circuitry and counters are probably fine.
So if it fails to count, I would say it's not due to the counter/drivers/display boards, but rather the main board where all the magic happens. Could be many things causing this problem.

Also, I noticed that the overall brightness of the display sometimes fluctuates, dims and comes back up a second later. So I guess the caps in the HV section supplying the tubes, are "reforming"... and would need replaced probably.

Anyway, I will play with it a bit this week-end I think.  Take it apart, give it a good clean, see if I am lucky enough that it can be fixed easily this week-end.
That would be awesome. I really would like to be able to fix this one, so that I have at least one good / working meter that I can then use to help me troubleshoot my other two meters that have been resisting me for what feels like eternity now.

Wish me luck ! 

[duckduck]

<SNIP>
Found this beauty on leboncoin.fr for only 50 Euros.... 6 weeks later the deal is finally done and I received it today 

A Rochar A.1335 Neeksee DVM

I know, I know.... I already have two of these.... but, I love them, and they are very, very sick and I am struggling to fix them.
So I though having a third one for spares or to take measurements, couldn't be a bad thing eh...
Plus, this one is the luxurious version of this meter, i.e. it's got auto-ranging and can do AC as well as DC.
The base model is manual ranging and can only do DC.
<SNIP>

An autoranging nic-C meter that does AC and DC? I'm jealous.

[salvagedcircuitry]

This week on All Boat Anchors Go to Heaven....
A very sad and neglected HP 3585A spectrum analyzer is on the operating table.
Powers up but no signs of life on the display. Front panel lights up like a Christmas tree and the buttons are all mushy.
On first analysis, most of the slotted cards look dirty but A85 looks like it gave up the ghost.
Ultrasonic machine is working double duty but there is clearly surgery coming up soon. 

[salvagedcircuitry]

One 3585A has entered the building

[W6EL]

One 3585A has entered the building

NICE!

Alright, so how'd you do it?

Also, tell us your ultrasonic cleaning technique with the zip-lock bag. I haven't seen that before.

[W6EL]

Many things got repaired this week. I have some photos too.

First off, calibrated the HP 400EL and HP 3400A meters. This was fun. It wasn't as difficult as I thought it would be, especially after the first one. I did find one resistor on the "1/10th scale" adjustment was quite a ways out. A 38K resistor was coming up at around 38.8k, and that was enough to prevent it from coming up correctly. It's a 200 ohm pot, so this little drift had some bad effects on it. Once replaced, all was well, and it went right to where it was supposed to.

Along the way, I noticed that my signal generators all have very slight differences in their own "flatness", and I have to say, I do not have test equipment that is calibrated enough to really be sure which device is better in-cal. Fortunately at the 1% level they are flat, so HP 3400A cal went fine. Two of my 3400A meters seem to have a little "dent" in their frequency response, right around 5 MHz. They sort of dip down about 2% and then come back up a few MHz later. I can't seem to get it worked out, but I think it is basically in-spec. These are the two newer ones. The older one doesn't exhibit this. I went around and re-cal'd a few times but it's still there. I'm not gonna have a heart attack over it though. I think the spec for these meters is something like "+/- 2% above 5 MHz" or something. I can't remember.

I found the technique of calibrating the amplifier via the DC output jack and then following up with the meter calibration sensible.

Alright, so the next patient is my Tenma 72-910 audio oscillator. This is also known as the "Audio Oscillator 8204A" and "Protek B-820". I can't find a service manual anywhere or even a user manual. Anyway, despite it's low price ($40 at the thrift store), it works well. Audio is quite flat all the way up. Metal film resistors throughout (where it counts). SNR is about 60-65dB. But I have noticed that there is a little 60/120 cycle that sneaks in at around -40dBc. It's not easy to hear but you'll see it on an FFT if you zoom in. So anyway, I figured, I'd go in there and replace some old tired caps and fix that right up. Well, no, it was more tricky than this.

There are three rails inside. +12, -12, and +8. The unregulated ~10VDC feeding the 7808 had about 300mVRMS of hum on it. I pop'd thte 2200 uF cap out, replaced it with a brand new one, and... it was still there! The other rails were around 10mV, for reference. I'm not sure why this one would be so much higher than the others. It's not from a center-tapped coil on the transformer, which the +/-12V rail is, so maybe that is part of it. At any rate, I threw a 10,000uF cap in the same place as the 2200uF cap and that was the end of it, no more hum! I also zip-tied the AC mains wires, which go to the power switch on the front panel, to the side of the chassis while I was in there. I measured no effects from it other than feeling better about it. I found this device kind of interesting. There's one chip in the synthasis portion of the device which I could not identify, OKI M5502. Also there appears to be a temperature sensor used, possibly for corrections? Lastly, I did notice an unfortunate increase in distortion when driving low loads and also when using the attenuator. Maybe a proper buffer circuit will happen some day for this device, we will see. The reference crystal is 3.2768 MHz, so no 10 MHz inject happening here.

Patient number 3 is my Tenma 72-410A Bench DMM. This is also known as LG DM-441B and possibly EZ Digital DM-441B. I've always liked this meter due to the bright LED display. You can view this thing from any angle and with any lighting situation. It has a Maxim RMS converter (MX536 I believe) and one of those standard looks-like-a-transistor 2.5V reference jobs. The ADC and LED display driver is one chip which is simply DC in and LED segments out. It was probably never designed to impress, but I do like it anyway. Except for a few things. Annoying thermal drift (and this is why the zero adjustment is on the front panel), and unequal frequency response. The thing was sold with a big "CALIBRATION FAILED" sticker on top, so, I knew this going in a few years ago when I got it.

I figured I'd break out the old golden screw driver and get it all fixed up. And so, with my meager equipment, I got through the DC and low frequency calibration just fine. No, I do not have a 1000V source. I'll skip that for this meter!

With the high frequency cal, I could not get it to meet spec at the required 10 KHz and 50 KHz points. It was out by 15%! We can't have that, can we? I took the metal shield off and found a few things. For one, someone had passed this huge orange wire, used for the 10A current reading, over top of one of the AC compensating circuits. Moving it a little to the side got me much closer. But also, I had to change two capacitors out to get it really dialed in. You can see the ugly bodging in the photos. Not pretty. But, once complete, it's rocking much more flat out to 50 KHz. I'll have to run a curve on it to really know for sure, but it seems really good.

I do want to eventually go in there and resolve the zero-shift. I think some modern low-offset op-amps and an improved power rail balance scheme will do the trick. Currently they use 5.1V zener diodes at each op-amp with lovely 5% resistors. But of course, they did not place the zeners together, and they have aged, and of course, noise, etc. PPMs leaking everywhere. This is not the way. I will give it the treatment when I get around to it. 

So yeah, that was fun. I have taken a look at the HP 3490A calibration steps and I am a bit overwhelmed. I will probably skip the 1000V 100KHz source for now...

Y'all are doing some neat projects, so great to read, great work everyone, nice progress on our multi-step program.

[Black Phoenix]

TERRA Operative, I have something for you...







Next week I will sent you. I didn't had time this week to do it. Tracking no will be sent via PM.

Also as we talk, it have some problems, as bad contact on the selector wheel, it is not reading correctly currents via the clamp. But it have all the parts you required for your own clamp, so use it as a donor.

[factory]

Many things got repaired this week. I have some photos too.

...snip...

Alright, so the next patient is my Tenma 72-910 audio oscillator. This is also known as the "Audio Oscillator 8204A" and "Protek B-820". I can't find a service manual anywhere or even a user manual. Anyway, despite it's low price ($40 at the thrift store), it works well. Audio is quite flat all the way up. Metal film resistors throughout (where it counts). SNR is about 60-65dB. But I have noticed that there is a little 60/120 cycle that sneaks in at around -40dBc. It's not easy to hear but you'll see it on an FFT if you zoom in. So anyway, I figured, I'd go in there and replace some old tired caps and fix that right up. Well, no, it was more tricky than this.

There are three rails inside. +12, -12, and +8. The unregulated ~10VDC feeding the 7808 had about 300mVRMS of hum on it. I pop'd thte 2200 uF cap out, replaced it with a brand new one, and... it was still there! The other rails were around 10mV, for reference. I'm not sure why this one would be so much higher than the others. It's not from a center-tapped coil on the transformer, which the +/-12V rail is, so maybe that is part of it. At any rate, I threw a 10,000uF cap in the same place as the 2200uF cap and that was the end of it, no more hum! I also zip-tied the AC mains wires, which go to the power switch on the front panel, to the side of the chassis while I was in there. I measured no effects from it other than feeling better about it. I found this device kind of interesting. There's one chip in the synthasis portion of the device which I could not identify, OKI M5502. Also there appears to be a temperature sensor used, possibly for corrections? Lastly, I did notice an unfortunate increase in distortion when driving low loads and also when using the attenuator. Maybe a proper buffer circuit will happen some day for this device, we will see. The reference crystal is 3.2768 MHz, so no 10 MHz inject happening here.

That Tenma oscillator has a frequency counter input too, that ICs above & below to the crystal look counter related (note where the counter input lead is going too), two 74LS390 dual dividers, the 4511 is the BCD decoder/latch for the 7 segment LED display, possible the M5502 is part of the display multiplexing. I'm guessing the audio oscillator section is all analog, can't tell from the picture.

Edit: It's a rebranded Hung Chang 8204a, instructions confirm the counter part; https://e-l.unifi.it/pluginfile.php/641909/mod_folder/content/0/Generatori%20tensione/HUNG_CHANG_8204A.pdf?forcedownload=1

David

[factory]

One 3585A has entered the building

NICE!

Alright, so how'd you do it?

Also, tell us your ultrasonic cleaning technique with the zip-lock bag. I haven't seen that before.

Isn't that a way of saving on the cleaning chemicals? Keep the fresh cleaner stuff in the bag with the part being cleaned, anything else lower cost liquid outside.

The SA looks familiar, sure I've seen one missing the control and panel CRT recently.

We once had the bigger brother to that Crest cleaner at work, two cleaning tanks, two rinse tanks, two drying stages and automated loader, cost an absolute fortune in the early 90s, I miss not having access to it, they got rid of it when they EOL'ed the lab.

David

[Robert763]

Also allows you to not mix chemicals. If you have water based cleaner in the tank and you want to do a item with IPA or similar you don't have to empty the tank. The use of a sub container be it a bag or tub can allow you to clean larger items because the sound waves transfer through the walls and into the other container.

[m k]

Thank you, Vince!
It was also even cheaper than I thought.

Digits will be maybe a half height lower but should be clearly visible.
If not then there's still some tilting available.

180V power is in the background.
I've now learned that trial and error with E12 x 10^4 is not refreshing.
So it's now putting out around 4.9mA and that it must be.

I thought resistors of same set would be close to each other but these 10^4 things are something else.

That China goods double meter is also pretty useless, but it's still there since it's there already.
Maybe first decimal accuracy tops, and for tens of volts and over an amp of current.
Current is now changed to 1000x but not tested yet.

[W6EL]

That Tenma oscillator has a frequency counter input too, that ICs above & below to the crystal look counter related (note where the counter input lead is going too), two 74LS390 dual dividers, the 4511 is the BCD decoder/latch for the 7 segment LED display, possible the M5502 is part of the display multiplexing. I'm guessing the audio oscillator section is all analog, can't tell from the picture.

Edit: It's a rebranded Hung Chang 8204a, instructions confirm the counter part; https://e-l.unifi.it/pluginfile.php/641909/mod_folder/content/0/Generatori%20tensione/HUNG_CHANG_8204A.pdf?forcedownload=1

David

David,

Amazing catch on the additional model of the oscillator. I've never seen this one. I will have to see if anyone has a schematic, because it would be interesting to see exactly what's going on with it. I have never gotten the SYNC connector to do anything, for example, but maybe I'm not understanding it correctly. I figured it was to provide a little forcing function to whatever is oscillating inside it, which would cause it to sync to the provided signal, but I've yet to see any signal I put in make a drop of difference on the output.

Here's some more pics if anyone is interested.

--E

[salvagedcircuitry]

One 3585A has entered the building

NICE!

Alright, so how'd you do it?
Also, tell us your ultrasonic cleaning technique with the zip-lock bag. I haven't seen that before.

Thanks! The 650uf capacitor on board A85 died. It was a standard 20% capacitor and it leaked on the portion of the board with the two precise 1.0% kemet 47uF foil wound capacitors. Luckily because HP hard gold plated every board in this fellow, the failed cap did not tarnish the traces much at all. Its kinda incredible actually. I've had other boards where the failed caps ate the traces. Not here!
It was the first time I tried the plastic bag method. Traditionally, I've been using glass containers inside larger ultrasonic machines to save on cleaning fluid, but this time I did not have one big enough. My brother suggested the plastic bag method and it worked great! I thought I would need a rigid container as most of the ultrasonic documentation from various vendors calls for a rigid glass container. You can even buy beaker holders from most legitimate ultrasonic vendors. What was nice here is that since all the parts are through hole, I could get away with using my 40khz ultrasonic and not use my 135khz unit which would have taken a lot longer to get the same result. One of the boards I debated on cleaning had a very oven sealed looking component so I skipped that and used a toothbrush and ipa. Rather be safe than EOL.

Isn't that a way of saving on the cleaning chemicals? Keep the fresh cleaner stuff in the bag with the part being cleaned, anything else lower cost liquid outside.

The SA looks familiar, sure I've seen one missing the control and panel CRT recently.

We once had the bigger brother to that Crest cleaner at work, two cleaning tanks, two rinse tanks, two drying stages and automated loader, cost an absolute fortune in the early 90s, I miss not having access to it, they got rid of it when they EOL'ed the lab.
David

My crest is nice, but it is a desktop ultrasonic targeted toward consumer use. The one you are describing is likely a stout commercial version with external transducers and or a vapor depotision unit. Those are truly drool worthy and big$.

Also allows you to not mix chemicals. If you have water based cleaner in the tank and you want to do a item with IPA or similar you don't have to empty the tank. The use of a sub container be it a bag or tub can allow you to clean larger items because the sound waves transfer through the walls and into the other container.

Correct indeed!

[Vince]

Some good news.... this week I finally... finally managed to sell these 33/303 Vintage QUAD amps I repaired.
Took 6 months no less. Starting price 500 Euros which was  plenty consistent with other ads... but no takers so had to keep dropping the price every other week and 6 months later it finally went for 350 Euros. Well below prices I see everywhere.... except mine did sell, but the other ads just rot there forever. So I think sellers will have to come to their senses and realize people aren't capable or willing to splash ridiculous amounts of cash for old stuff anymore.

I probably spent 50 to 75 Euros in parts so not that big a win compared to what on-line ads had me dream of... but that's a real world price... what people actually are willing to pay right now. So.... it is what it is.

I had long given up making lots of money on these amps.. they drove me so crazy, all I wanted now was simply get them out the door, was fed up with them.

Buyer was decent, well, a bit troublesome like all buyers, but I put up with his crap so I could finally sell these amps and make some money.
He said he inherited from his uncle,  the matching QUAD "FM3" radio tuner. So now with my 33/303 combo, he has the complete set, which is cool.

You can't imagine how relieved I feel not to see these amps in the house anymore. I lost so much hair because of them.
Frees some very precious space in the lab / living room as well, which is priceless.

[Vgkid]

* snip *

After following your previous repairs on these units , I can tell that you are relieved to finally get rid of these units.

[TERRA Operative]

TERRA Operative, I have something for you...

Next week I will sent you. I didn't had time this week to do it. Tracking no will be sent via PM.

Also as we talk, it have some problems, as bad contact on the selector wheel, it is not reading correctly currents via the clamp. But it have all the parts you required for your own clamp, so use it as a donor.

Much thanks! 

I also have some things to send in return. Those watches (that tag and the first two watches on your list), so I'll pay for those tomorrow and have them send off mid-late next week.

[Vince]

OK ! I worked all evening and morning on the Rochar DVM.
I am lucky, this one is not causing too much trouble, I was able to revive it and make good progress, almost there.

1) Gave it a good clean, looks much more pleasing up close in the flesh now. Looks nice and not a bio-hazard any more 


2) Fixed the dead digit : was simply the tube itself that was dead (shit happens...) ... luckily I had a spare one... thanks to a generous TEA member who sent it to me some time ago. His identity shall remain preserved, but you know who you are, so thank you very much ! 

3) Looked under the chassis at the Vref board. It's got the same two big yellow dipped WW resistors with that special tempco, that I had trouble with, with my other meter... some may remember it ?



They were open-circuit because of moisture getting in somehow, and corroding the leads from the inside. Didn't know how they were constructed of course, so I sadly ruined them when trying to crack them open. So any repair was out of the question.

Anyway, in this meter same problem. One of the two yellow resistors measured open-circuit. Indeed you could see green stuff leaking were one of the leads traverses the yellow "jacket", for lack of a better term. This resistor was the one that's setting the charging current for ramp generator that does the voltage/time conversion. So I thought... open-circuit resistor means zero current charging the timing cap, hence no ramp, hence of course the instrument is unable to measure anything... so since this was identified as a show stopper, I decided to start the repair process from this angle, and go from there. There was no point troubleshooting anything until this problem was fixed.

So I tried to fix this resistor, to see if I could do better than last time. Yes indeed. I managed to crack it open without damaging the coils inside.




Noticed that on one end, the wire had come off the "cup" of the terminal. So I unwound the wire a bit, to get some slack, soldered the resistor back to the board, then tried to solder the wire to the board / terminal strip as well. I managed to do it after half a dozen attempts... the wire is so thin that it kept breaking when I worked it with the iron tip. Also, my tweezers are too big and crap quality to reliably grab that tiny wire. Not to mention I could barely see the wire with my naked eyes to begin with. The opti-visor came to the rescue but it was only good when inspecting the resistor up close... but working distance with this optivisor is too crap to let me do any soldering work, so had to solder pretty much blind, not really seeing that wire...  I took a pic up close, with a white sheet of paper to help see the wire.




Anyway, once soldered, the instrument as I hoped, was now alive ! It can take measurements ! 





4) ... but only in single-shot mode... the trigger circuitry had a problem. If I trigger manually, using the push-button, it works. But if I set the trigger to "AUTO" mode, it doesn't measure anything, no go.
Luckily I fixed it quickly, was easy : the trigger circuitry has x3 5uF axial electrolytic caps to get the oscillator/flip-flop of the AUTO mode going, as well as the reset circuitry. I tested them with the chinese component tester... all 3 were "Unknown or Damaged part"  woops.....replaced all 3 with "brand new" 40 year old NOS Nichicon 4.7uF caps I had in my stock, (radial sadly, of course) which somehow measured just fine on the chinese component tester..... AUTO mode now works fine ! 




5)  OK so at that point the meter basically works, I am overjoyed.
I then tested it with my chinese Vref that can output 2.5 / 5.0 / 7.5 / 10Volts.
On the "native" / 5V range, it didn't need much in term of zero and full scale calibration.
Then I tested the 50 and 500V ranges and they are slightly off (a few LSDs, still reasonable), so might play with calibrating those ranges once all else is all and good.

6) All these first steps went quite quickly... hadn't even yet taken the time to check the power supply... so I now did that. All seems good, slightly excessive ripple on some rails so might replace the filter caps later on, but for now the ripple is still plenty acceptable, I think, given that the meter... works. 
the 200V supply for the display tubes is not fluctuating any more, so I guess the caps have now reformed. Of course they must be on their way out, and will die soon I guess.... and unsurpringly this particular rails is the one having by far the most ripple, at 10V or so (didn't scope it, but the DMM says 3.1V, so make that times 3 or so to get actual peak to peak value).


7) So at that point I basically had a nice working meter, so I could now start testing it more thoroughly to shake more bugs. Bugs I found :

7.1)  On the 5V / most sensitive range, 1mv resolution, with the inputs floating, it displays zero at first but then it steadily, slowly increases, increased.... A cap must be charging somewhere... but where ?  Not overly concerned about that in the short term, given that as soon as you short the inputs it displays a solid "0000", so clearly whatever is causing the drift when floating, is not capable of travestying an actual measurement when you want to make one.

EDIT : checking the manual, it says the 5V range is super high-impedance, greater than a Tera ohm. So I guess it doesn't take much parasitic capacitance anywhere in the front-end, to cause the symptom I am seeing ? So chances are, it's not a fault, it's just normal behaviour...

7.2) Now for an actual problem : at first everything was fine when I was measuring the 10V output of my reference... meter would display "10.00", eh.  However after a while, it started spuriously displaying "12.00" instead... and as time went on, it's now pretty much et on 12V rather than 10.
Trying letting the meter cool down a bit, but when I powered it up again, it was set straight away to 12V rather than 10. So maybe not a heat related issue then... rather something that went wrong and is now permanently wrong... which in a way is a good thing since solid faults are of course so much easier to trouble shoot than random or spurious ones...
Anyway, I did some testing and it looks like the problem lies in the counter stage/Section of the display board n°2 (from the left) : when you trigger a measurement, all the counters / digits gets reset. This works fine. However where this particular board is having is a problem, is when it wants to "reset" when it overflows :you reset it, then it can count just fine from 0 to 9, BUT if it needs to overflow and roll back to 0... it rolls back to '2' instead.  So I guess I need to look at the schematic of the counter of that board, and try to understand what could be going wrong.


So overall I am quite happy. it's in good nick, inside out, and basically works, almost, just fine, after only a day working on it.

So since it's going quite well, I will keep working on it in the coming days. Try first to fix that counting issue, then replace a cap or two, then do some more restoration work. Need to fix the usual problem of the orange colour filter falling off thanks to the foam holding it in place, turning to dust.
Also noticed, buried, hidden behind the front panel by the input jack, an electrolytic cap in series with a resistor, wired across the negative jack and earth/chassis jack. Cap seals do'nt look great and the resistor is clearly cooked.

[Black Phoenix]

TERRA Operative, I have something for you...

Next week I will sent you. I didn't had time this week to do it. Tracking no will be sent via PM.

Also as we talk, it have some problems, as bad contact on the selector wheel, it is not reading correctly currents via the clamp. But it have all the parts you required for your own clamp, so use it as a donor.

Much thanks! 

I also have some things to send in return. Those watches (that tag and the first two watches on your list), so I'll pay for those tomorrow and have them send off mid-late next week.

No worries, I still didn't gave you the shipping address...

[W6EL]

Vince, that Rochar DVM is wild.

My DMM is far less wild although it is interesting. I took a closer look at my HP 3490A.

I decided to just go through some of the adjustment steps and see where things are. And that's where I found that the -30V regulated DC rail had 6V AC riding along side it! Yikes! That poor integrator circuit runs off +/-30V and it was bopping up and down all the time.

A few new caps later this thing is really doing very well. All the internal tests pass. Accuracy seems quite good considering I have not tried calibrating it yet. Exactly how I calibrate a 6 digit meter will be interesting. The 10V reference inside it seems dead-on. Readings agree with my poor 4-digit meters down to the last digit on the 4-digit meters.

So then I took a look around. Beauty everywhere. Red 0.005% HP branded resistors and large fat TRW capacitors. Gold traces, many without solder mask, shining like mirrors. I don't even know where to begin. Just really nice stuff.

This brings me to the RMS modification I was thinking of doing. It's gonna be tricky. I thought I would perhaps short CR14 and CR15 (have not done this yet, to be clear), making the amplifier an AC amplifier (without rectification), and then feed that into the RMS chip and simply pass on the DC to the next stage (LPF and then an integrator). However, the amplifier that HP implemented is really not all that great. There is *significant* non-linearity around the lower 25% of each voltage range, and also a lot of what looks like crossover distortion (possibly from Q4 and Q5?). I guess this is why the specifications are best in "the zone" of that upper 75% of each range. Anyway, there's simply no point in taking this ugly signal and taking the RMS of it. The only way to really do this is to replace the U4-U3-Q2 loop with a modern op-amp and the RMS converter. I mean, maybe... maybe I can remove all these nasty limiters and remove the unbiased Q4/Q5 buffers... maybe? Thoughts?

I am sympathetic that it is from 1978 and only designed for a scaled average rectified value. I get that, not dogging on the HP engineers and their early op-amps!

[Peter_O]

Finally I closed my search filters on a variac.
Because I wanted one with sufficient power, well build, and minimal, I've had an eye on those old Philips style ones.
No voltmeter no anything. In case needed, I have some DVMs available.   

Now I managed to get a 1kW new old stock one.
It came in the original packaging, mounted on the shipment board and with spec sheet and original rubber feet.

[Vince]

Looks nice, I too plan  on getting a kW variac to restore all my old hollow-state scopes and what not.
However I thought I was warned here that getting an old variac  or isolation transformer was not advisable because they were not designed to safely cope with the increased mains voltage that we have nowadays ?!

[Robert763]

Looks nice, I too plan  on getting a kW variac to restore all my old hollow-state scopes and what not.
However I thought I was warned here that getting an old variac  or isolation transformer was not advisable because they were not designed to safely cope with the increased mains voltage that we have nowadays ?!

I don't know who said that but they are wrong. Unless you buy an american one only intended for 60Hz 
Any decent variac will handle the "increased" voltage since harmonistion across Europe. In reality nothing should have changes as the "new" voltage was within the tolance band of the old one.
If you are worried, many variacs have a "boost" function that allows an increase of voltage above the line voltage. They are rated for the line voltage at this tap which is below the end of the winding. If you connect the input to the end of the winding (100% connection) rather than the "boost" tap the input voltage rating boes up to the boost rating, typically 15% higher than the normal line input rating so about 250V for a "220V" rated variac.

Robert.

[Vince]

Vince, that Rochar DVM is wild.

My DMM is far less wild although it is interesting. I took a closer look at my HP 3490A.

You might like / remember its bigger brother I have as well... the Rochar type A.1466

More accurate, with a plug-in design, and 25,000 counts, and some gold as well...
Sadly mine came with the most common plug-in which, although it does Voltage and Current which is cool, does only DC and no auto-range.
You can't have it all I guess.

However it's got a great excursion. It can measure voltage from as low as 1µV up to bloody 2,000V
Current can go down to 1uA as well.

There exists a plug-in that does 4-wire resistance measurements, would love to have that...might try to track one of these down one day....

So then I took a look around. Beauty everywhere. Red 0.005% HP branded resistors and large fat TRW capacitors. Gold traces, many without solder mask, shining like mirrors. I don't even know where to begin. Just really nice stuff.

Sometimes I wonder how "real" these ultra high precision resistors really are...
I mean, with such spectacular precision, wouldn't the temperature induced variations overwhelm / ruin this precision, and make it just a dream ?!
Or is it so that HP expects / relies on the fact that the instrument will be in a lab between 19 and 21 degrees all year long, then knowing the self heating from the instrument itself, they calculated and validated experimentally that the temperature of these resistors inside the instrument, varies only by 0.5 °C tops, and that this temperature variation induces a change of resistance that's 5 or 10 times less than the 0.00000000005% that they claim ?

I don't know, but sometimes I do wonder about the reality of these ultra high precision voltmeters/X/Y/Z .... 

[Vince]

Looks nice, I too plan  on getting a kW variac to restore all my old hollow-state scopes and what not.
However I thought I was warned here that getting an old variac  or isolation transformer was not advisable because they were not designed to safely cope with the increased mains voltage that we have nowadays ?!

I don't know who said that but they are wrong. Unless you buy an american one only intended for 60Hz 
Any decent variac will handle the "increased" voltage since harmonistion across Europe. In reality nothing should have changes as the "new" voltage was within the tolance band of the old one.
If you are worried, many variacs have a "boost" function that allows an increase of voltage above the line voltage. They are rated for the line voltage at this tap which is below the end of the winding. If you connect the input to the end of the winding (100% connection) rather than the "boost" tap the input voltage rating boes up to the boost rating, typically 15% higher than the normal line input rating so about 250V for a "220V" rated variac.

Robert.

Oh that's great thanks ! So I can get a cheaper old used one then, no need to splash an arm for a brand new one...

[Peter_O]

Oh that's great thanks ! So I can get a cheaper old used one then, no need to splash an arm for a brand new one...

Unless the seller has tormented it near to core meltdown, espeacially in case you are hunting for a combined variac and isolating transformer. 
I bought a brand new isolation transformer some months ago separately and will combine it with this guy.