Test Equipment Anonymous (TEA) group therapy thread

[mnementh]

mnem
Well hell.

[Robert763]

Cheap HV probe on ebay this morning. 26$

https://www.ebay.com/itm/BECKMAN-INDUSTRIAL-HV231-22-HIGH-VOLTAGE-PROBE/274689423954

I don't like the hook on the end. When measuring HV my mantra is get on and get off ASAP. With that hook you could easily get hung up. 

My thoughts precisely.

Hook unscrews, there should be a point with it. If mising can be made from metal PCB pillar with male end turned / filed down.
Idea of the hook is you connect with power off, stand back switch on, take reading (no touchy), power off, probe un-hooked.

  Din't read all the posts, answered already - sorry.

[Robert763]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

You can tell them apart by the reduced or missing dielectric, like this random 75 Ohm BNC Tee.

Those are the modern "compatable" type. The original 75R BNCs had full dielectric coverage and smaller diameter center pins. These have better match and lesss reflections than the modgern ones but if you plug a male 50R or "new" 75R into a original 75R female it will deform the contacts and the female won't connect reliably to an original 75R. An original 75R male won't make reliable contact with any 50R or "new" 75R.
Fortunatly original 75R connectors are rare. The center pin is noticably thinner.

[Ero-Shan]

@tautech:

I think, I'll order next month an electronic load from Maynuo @Welectron.
This one: https://www.welectron.com/Maynuo-M9812-Electronic-Load

What do you think is a similar device (tech-spec wise) from Siglent?
What would you recommend?

Thank you for your answer.

Could I perhaps interest you in a Chroma load?

Thanks, those are nice units but they do not fit my specs. 60V is too low for what I need.
Btw, I had already checked out your store, I always do this on a regular basis.   

I have two electronic loads: A Zentro ELA 40/40D (40 V/ 40 A, 200 W) and a TET 60 V/ 100 A. Alas the latter is dead, and there's absolutely nothing to find about it. I opened it once and and looked for something to measure, like a supply voltage, when suddenly both supersonic wind tunnels sprang into action, startling me to death. Still, it didn't work. And even after looking for half an hour, I hadn't find a way to disassemble it. My relationship with mechanical engineers is a bit strained.

I sure would like to have a load that works at a higher voltage. I don't need 100 amps, not even 40. Say 400 V/12 A should satisfy all my needs.

[Kosmic]

Cheap HV probe on ebay this morning. 26$

https://www.ebay.com/itm/BECKMAN-INDUSTRIAL-HV231-22-HIGH-VOLTAGE-PROBE/274689423954

That tempted me at first glance but looking at the label on the handle, it's designed to pair with a 22 M\$\Omega\$ input impedance meter.  I can't think of one offhand that's suitable to pair with that probe.  At least, I know for sure I don't have something that would work correctly with that.  Maybe that's the reason for the price?

Woah, I completely missed that part. I found some specs online and they were talking 10M. I guess it was the model HV321-10. 22M is weird. I don't think I even seen a meter with a 22M input impedance.

[SilverSolder]

@tautech:

I think, I'll order next month an electronic load from Maynuo @Welectron.
This one: https://www.welectron.com/Maynuo-M9812-Electronic-Load

What do you think is a similar device (tech-spec wise) from Siglent?
What would you recommend?

Thank you for your answer.

Could I perhaps interest you in a Chroma load?

Thanks, those are nice units but they do not fit my specs. 60V is too low for what I need.
Btw, I had already checked out your store, I always do this on a regular basis.   

I have two electronic loads: A Zentro ELA 40/40D (40 V/ 40 A, 200 W) and a TET 60 V/ 100 A. Alas the latter is dead, and there's absolutely nothing to find about it. I opened it once and and looked for something to measure, like a supply voltage, when suddenly both supersonic wind tunnels sprang into action, startling me to death. Still, it didn't work. And even after looking for half an hour, I hadn't find a way to disassemble it. My relationship with mechanical engineers is a bit strained.

I sure would like to have a load that works at a higher voltage. I don't need 100 amps, not even 40. Say 400 V/12 A should satisfy all my needs.

Wonder if it is possible to cobble together a relatively simple "high voltage front end" for a regular electronic load?

[Robert763]

I am aware of this. I'm weak in the math, but I understand the principles involved. I also know that in many cases, as per the discussion I linked to, the specification is not adhered to very well. EDIT: I also understand that is primarily due to a combination of short cable length and low frequency and low-power signal making it possible to get away with that misuse.

The advent of PTFe-dielectric cable and connectors has made some difference here; the near-neutral velocity factor thereof makes the calculations we use for making a SMA feed-cable on our RC transmitters, for example, a little simpler.

mnem
 

If we ignore power transfer (becasue it's not important for small signals) if the cable electrical lengthe is less than 1/4 wavelength of the frequency in use (or 1/ pulse width) then connector / cable impedance matching is not critical. Impedance mismatches cause reflections which are what causes issues.

[Robert763]

 

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

You can tell them apart by the reduced or missing dielectric, like this random 75 Ohm BNC Tee.

Those are the modern "compatable" type. The original 75R BNCs had full dielectric coverage and smaller diameter center pins. These have better match and lesss reflections than the modgern ones but if you plug a male 50R or "new" 75R into a original 75R female it will deform the contacts and the female won't connect reliably to an original 75R. An original 75R male won't make reliable contact with any 50R or "new" 75R.
Fortunatly original 75R connectors are rare. The center pin is noticably thinner.

  did it agian (not read all posts.)

[Cerebus]

My relationship with mechanical engineers is a bit strained.

I'm sure that if you screw your courage to the sticking post, spend some time down the mill, learn the drill, eventually you'll find a way to turn your hand to it and take the stress out of the strained situation.. 

[tggzzz]

Din't read all the posts, answered already - sorry.

I've never ever ever done that. Oh no.

More seriously, duplicating an opinion/technique is useful, just as repeating an experiment is useful.

[mnementh]

I am aware of this. I'm weak in the math, but I understand the principles involved. I also know that in many cases, as per the discussion I linked to, the specification is not adhered to very well. EDIT: I also understand that is primarily due to a combination of short cable length and low frequency and low-power signal making it possible to get away with that misuse.

The advent of PTFe-dielectric cable and connectors has made some difference here; the near-neutral near-ideal velocity factor thereof makes the calculations we use for making a SMA feed-cable on our RC transmitters, for example, a little simpler.

mnem
 

If we ignore power transfer (becasue it's not important for small signals) if the cable electrical lengthe is less than 1/4 wavelength of the frequency in use (or 1/ pulse width) then connector / cable impedance matching is not critical. Impedance mismatches cause reflections which are what causes issues.

That sounds like a good nutshell analysis of why all the RF guys say "Anything lower than x is DC..." yet the actual value of x seems to vary from a few MHz to a few GHz depending on their mood vs what bit of gear they have in front of them... 

mnem
 

[PA0PBZ]

Re: Electronic loads: After having the parts to build one on the shelf for like 5 years I bought one of those:



https://nl.aliexpress.com/item/4000580653360.html?spm=a2g0s.12269583.0.0.35ff2d2832gPfP

CV, CC, CP and CR, 220V/20A/150W, color display, bluetooth, app. 25 eurobucks, No idea how they make money on this 

[AVGresponding]

mnem
Well hell.

Watched that last year sometime, pretty interesting what you can do with a stubborn streak and a shitload of relays.



Some classic UK children's TV for you:

[mnementh]

That Bagpuss thing was definitely much better played at 2X speed. This too. 

mnem
*toddles off in search of dragon cookies*

[BU508A]

Re: Electronic loads: After having the parts to build one on the shelf for like 5 years I bought one of those:



https://nl.aliexpress.com/item/4000580653360.html?spm=a2g0s.12269583.0.0.35ff2d2832gPfP

CV, CC, CP and CR, 220V/20A/150W, color display, bluetooth, app. 25 eurobucks, No idea how they make money on this 

Seems there are two versions around:

[tautech]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

[factory]

Cheap HV probe on ebay this morning. 26$

https://www.ebay.com/itm/BECKMAN-INDUSTRIAL-HV231-22-HIGH-VOLTAGE-PROBE/274689423954

That tempted me at first glance but looking at the label on the handle, it's designed to pair with a 22 M\$\Omega\$ input impedance meter.  I can't think of one offhand that's suitable to pair with that probe.  At least, I know for sure I don't have something that would work correctly with that.  Maybe that's the reason for the price?

Woah, I completely missed that part. I found some specs online and they were talking 10M. I guess it was the model HV321-10. 22M is weird. I don't think I even seen a meter with a 22M input impedance.

You have now, my old Beckman 310 has a 22MΩ input impedance for Vdc (warning 2, 20 & 200 Kelvin Ω ranges may trigger  );


The newer Wavetek (took over Beckman) HD160B isn't 22MΩ, but still has the 1500Vdc range as the older meters do.

I agree with hooking the probe on before power-up, something Shango066 does on many TV resurrections to monitor the HT voltage (a common problem area with ancient TV's) while bringing them up with lamp-limiter and/or variac and while capacitors are reforming.

David

[factory]

Have you been changing out lots of them because they are really unreliable or something?

David

No, this is just as part of a scheduled rewire/refit, which is invariably a blunt instrument here, and can bag you some nice fittings from time to time. The ones I took out are identical to the one you pictured, with the possible exception of the battery; these are a slightly older 3S sub-C Ni-Cd pack, and newer ones will have 1S Li-ion packs.

However, during my time on the maintenance side, doing the fire alarm and EL testing I did notice that the cheaper LED fittings (even when from well known manufacturers) are appallingly unreliable, way more so than older fluo jobbies.

Odd this one still uses Ni-Cd, the new 3V LDO sorted it out and it's now back with it's owner.


Those square LED ceiling panels seem to be utter crap at work, so many have died in the toilet block leaving some areas in complete darkness, last failure took out about half a dozen of them, took maintenance several days to sort that mess out. They are extra annoying as the whole panel fails too, something which was very rare with the quad tube based panels they replaced. 

David

[Cerebus]

What you don't want to see on your United Airlines flight 328 from Denver to Honolulu:



(It landed safely.)

[Specmaster]

Have you been changing out lots of them because they are really unreliable or something?

David

No, this is just as part of a scheduled rewire/refit, which is invariably a blunt instrument here, and can bag you some nice fittings from time to time. The ones I took out are identical to the one you pictured, with the possible exception of the battery; these are a slightly older 3S sub-C Ni-Cd pack, and newer ones will have 1S Li-ion packs.

However, during my time on the maintenance side, doing the fire alarm and EL testing I did notice that the cheaper LED fittings (even when from well known manufacturers) are appallingly unreliable, way more so than older fluo jobbies.

Odd this one still uses Ni-Cd, the new 3V LDO sorted it out and it's now back with it's owner.


Those square LED ceiling panels seem to be utter crap at work, so many have died in the toilet block leaving some areas in complete darkness, last failure took out about half a dozen of them, took maintenance several days to sort that mess out. They are extra annoying as the whole panel fails too, something which was very rare with the quad tube based panels they replaced. 

David

Yeah, there are loads of cheap Chinese imports knocking around the wholesalers, they also have horrible drive characteristics as well.

[Specmaster]

What you don't want to see on your United Airlines flight 328 from Denver to Honolulu:



(It landed safely.)

You're not kidding, I bet there was a few soiled pants on that flight when it landed.

[factory]

Sort of TEA related (has a voltmeter built in), I posted a pic of my shed radio (a Danish made Sailor 16T) a while ago and someone on here was interested in seeing inside it, well I've finally had enough of the voltmeter under-reading and decided to adjust it.

A quick teardown, this radio uses a lot of those Mullard/Philips AF11x series transistors that have a bad reputation of failing with tin-whisker related shorts, despite this I haven't had any trouble with them yet.




Here is the problem I have, with an external supply set for 9V I get a reading of approx 8V of the built in meter.


Having a look at the circuit diagram they used a 10kΩ resistor in series with the meter with no provision for adjustment, it's on the power switch (arrowed).


A decade resistor was used to determine what value could be added in parallel to give a better reading, I came to the conclusion the best compromise was 83kΩ, I used a 120kΩ & 270kΩ in parallel across the original resistor.


All back together with fresh set of 6 D sized leak-tubes. 


David

[Cerebus]

What you don't want to see on your United Airlines flight 328 from Denver to Honolulu:



(It landed safely.)

You're not kidding, I bet there was a few soiled pants on that flight when it landed.

Yeah. I remember when "Fly United" made me think of this:



not this:

[tautech]

A quick teardown, this radio uses a lot of those Mullard/Philips AF11x series transistors that have a bad reputation of failing with tin-whisker related shorts, despite this I haven't had any trouble with them yet.
David

Where, them mighty hard to spot ?
In the tin cans ?
 

[Specmaster]

Sort of TEA related (has a voltmeter built in), I posted a pic of my shed radio (a Danish made Sailor 16T) a while ago and someone on here was interested in seeing inside it, well I've finally had enough of the voltmeter under-reading and decided to adjust it.

A quick teardown, this radio uses a lot of those Mullard/Philips AF11x series transistors that have a bad reputation of failing with tin-whisker related shorts, despite this I haven't had any trouble with them yet.




Here is the problem I have, with an external supply set for 9V I get a reading of approx 8V of the built in meter.


Having a look at the circuit diagram they used a 10kΩ resistor in series with the meter with no provision for adjustment, it's on the power switch (arrowed).


A decade resistor was used to determine what value could be added in parallel to give a better reading, I came to the conclusion the best compromise was 83kΩ, I used a 120kΩ & 270kΩ in parallel across the original resistor.


All back together with fresh set of 6 D sized leak-tubes. 


David

I have never before come across a radio which has NW on its dial and range switch, WTF is that then?