HV multimeter probe : buying advice ? - Page 1
Forum section: electronics / testgear

author: Vince
author_rank: Super Contributor
timestamp: October 03, 2017, 11:21:12 pm
content: Hi there,I am planning on getting a high-voltage probe for use with a multimeter.I have absolutely no idea how much I should be spending to get something half decent that will not blow my face.Is there a particularly popular product at the moment that I should be aware of ? Brand/model ?Spec wise, I need something that's designed to work with the usual 10Mohm input impedance of most DMM.Rating : I want to buy it mostly to be able to work on old instruments that use CRT's (mostly my "collection" of old scopes, to start with) That is, small tubes, not big television sets.My immediate need is for a Tek 317 scope which uses a HV of 7.7kV (tiny 3inch tube) My Tek 2232 scope uses 12kV for its CRT so I would need to be able to measure at least this. My other scopes I have no idea, but I guess/understand that the voltage is closely related to the size/diagonal of the tube, right ? So if guess a 15kV probe would cover most CRT instruments I might come across. 20kV would put me even more on the safe side.Are there standardized voltage ratings, like 10kV, 15kV, 20kV. or does each manufacturer come up with pretty much anything and everything, depending on mood ?I am looking at spending no more than 100 bucks grand maximum, for a 20kV probe. If limited to 15kV then hopefully less than this...Is this realistic or should I be better off buying a used old one on Ebay ? If so, any particular brand or model worth searching for ?Thanks in advance for your good advice if you know the subject with up to date information...--Vince

author: bd139
author_rank: Super Contributor
timestamp: October 03, 2017, 11:30:51 pm
content: You can get some reasonable ones rated up to 40kV on ebay. Mine is an unbranded "HVP-40". Cost me around £45 ($60). I've poked that in various things up to 20Kv or so and it's been fine. I have avoided hooking it up while the DUT is powered up though. Output is 1V per 1kV on a 10M Zin meter.

author: tautech
author_rank: Super Contributor
timestamp: October 03, 2017, 11:54:39 pm
content: Quote from: Vince on October 03, 2017, 11:21:12 pmNo you don't.PDA multipliers are either working or not and the CRT is the best indicator of that.Instead focus on being able to accurately measure the EHT, commonly in the 2-3 KV range and needs be adjusted to meet spec.Then the PDA multiplier just boosts this by its multiplier factor to whatever it is.

author: Vince
author_rank: Super Contributor
timestamp: October 04, 2017, 12:22:36 am
content: Quote from: tautech on October 03, 2017, 11:54:39 pmYes good point !.... However for educational purposes I would still like to be able to actually witness what's actually coming out of the anode...QuoteYes I guess that's true for "modern" '80s scopes like my 2232, but for example the Tek 317 I am hoping to start trouble shooting soon, has a multiplier made up of discrete components and I think something in it might be wrong. I want to be able to measure the voltage at various points in the multiplier so I can figure out what stage is faulty. From what I can see in the schematics, the multiplier is a 3 stage thing, each using a capacitor and diode/vacuum tube. Looks like a traditional voltage "multiplier" doubler but with a tube diode rather than a semi-conductor based diode.The trace on the screen gets dimmer and dimmer, so much as to become completely invisible, within only 30 to 60 seconds following power up.I suspect either the HV is faulty, or the brightness control circuitry, is. So my plan is to first measure the actual anode voltage. If it drops then I will look at the HV multiplier circuitry, but it if its healthy then I guess I would rather have to turn my attention to the brightness control section.My first guess is that the 55+ year old capacitors in the HV multiplier are leaky, seems common in these old tube instruments as I understand it.

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2017, 12:44:38 am
content: Of greatest concern for PDA measurement is loading as the PDA current is only a mA or two whereas the EHT can probably handle 20 mA loading. Either way DUT loading would be the first spec I'd be looking at to ensure a HV probe was suitable for your needs.Maybe this one, although my buy price is ~1/2 your limit:http://www.pintek.com.tw/product_detail/landersound/index.php?Product_SN=19259&Company_SN=6002&Product_Site_Classify_SN=17071Remember PDA voltages are + and EHT are negative WRT DUT ground.

author: Vince
author_rank: Super Contributor
timestamp: October 04, 2017, 01:38:01 am
content: Just for my information... what do the PDA and EHT acronyms actually stand for exactly ? From what you say I gather that PDA relates to the CRT anode/HV multiplier output voltage, and EHT relates to the various control grid voltages ?Pintek, rings a bell. didn't EEVBlog show one of these recently ?! This name sounds familiar...The Pintek HVP-40 40kV for DMM use looks fine for me, and well under 100 bucks so within my budget, great !Only 73 Euros / 65 Pounds from the UK :http://www.ebay.fr/itm/Piintek-High-Voltage-HVP40-probe-40KV-DC-28KV-AC-1000Mohm-1000-1-4-DMM-EUship-r-/381090989314?hash=item58bacb0502:g:6XAAAOSwFfhXjbgI.. and still in the UK, looks like you can get it even cheaper, rebranded as a "Testec" unit, for only 45 pounds. I assume this is what you bought unbranded, BD139 ??http://www.ebay.fr/itm/Testec-TT-HVP-40-High-Voltage-Probe-/152725491809?hash=item238f261061:g:XGsAAOSwwyZZ0Sml45 Pounds and still, they accept offers !I think I am very tempted...As for loading, they are 1000M so for an anode voltage of 10kV say, that's a load of only 10uA, way less than a mA then, so might work just fine...Quote from: TautechLink doesn't work... but I get the picture.. Pintek seems to fit my needs and budget...

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2017, 01:55:31 am
content: Quote from: Vince on October 04, 2017, 01:38:01 amExactly and CRT cathode, don't forget him.EHT = extra high tension, I use the term WRT CRO's to differentiate between CRT voltages and the HV that's used for the deflection plates, commonly ~150V+ that's much higher than anywhere else on a CRO.....excepting those old glowing ones full of tubes.PDA = post deflection acceleration....self explanatory.I see some of these terms used in different ways on the forum and I think CRO newbies would get confused and at one time I was too until I saw it laid out in this way in an old CRO service manual.Try this one:http://www.pintek.com.twLook for HVP40 in their HV probesBTW, the 2 HV probes you've linked are the same.....original and rebrand.

author: Vince
author_rank: Super Contributor
timestamp: October 04, 2017, 01:59:34 am
content: Thanks for the info .Link still doesn't work.. just give me the product name I will look it up on Pintek's website directly !

author: Vince
author_rank: Super Contributor
timestamp: October 04, 2017, 02:06:49 am
content: OK the HVP 40 ! Yes, that's exactly the one I mentioned earlier, that's the one I am interested in and I think also the one BD139 bought.I think your first link didn't work because it looked like it was some kind of PHP dynamic link with session and ID information in it, rather than a simple static link.

author: Vince
author_rank: Super Contributor
timestamp: October 04, 2017, 02:10:31 am
content: Quote from: tautech on October 04, 2017, 01:55:31 amYes I know, I did mention it !I will make an offer on the rebranded unit, no need to pay more for what is obviously the exact same product...

author: bd139
author_rank: Super Contributor
timestamp: October 04, 2017, 06:49:05 am
content: All the HVP-40 probes are made in the same Chinese sweat shop. Whichever brand you choose it’s going to be the same probe. Mine doesn’t even have a brand on it when I look at itWith respect to measurements, you do occasionally need to poke the PDA voltage. The multiplier tends to snuff it on some of the older scopes, particularly the 4xx ones I’ve noticed. First indication on a completely dead scope with controls that light up and a power supply that checks out is check the mutliplier input test point which is usually in the 2kV range. For that you need an HV probe anyway because even my funky new bench DMM only goes up to 1kV. If that checks out then you check the multiplier output.Current is around 10uA per 10kV so you’re not going to load it heavily.Note that leakage is dangerous at full whack so you need to keep the probe and the test site clean. Also don’t attach the probe to anything unless the unit is OFF to avoid accidents. O

author: Vince
author_rank: Super Contributor
timestamp: October 04, 2017, 12:17:25 pm
content: Thanks, can't wait to get that probe and start poking around that old 317 scope...

author: bd139
author_rank: Super Contributor
timestamp: October 04, 2017, 12:43:30 pm
content: Nice scope - please take some pictures if you get the time

author: Vince
author_rank: Super Contributor
timestamp: October 04, 2017, 01:25:17 pm
content: That's off topic but since my original question has been answered by now, I guess we can afford to drift a bit !Pictures were already taken, so here are some. Haven't done anything to it yet apart from opening it, so I still need to give it a good clean and do a little TLC, but overall it's in great nick.More on it to come soon if you are interested, as I intend to open a thread in the " Repair " section of the forum when I start working on it, in the coming weeks I expect, so stay tunedThere is also this video I found recently on YT, which you might like, a guy fixing his Tek 317 :

author: bd139
author_rank: Super Contributor
timestamp: October 04, 2017, 01:32:11 pm
content: Excellent - thanks for posting the photos. Certainly in good condition that one. Good luck with the repairs

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2017, 06:11:24 pm
content: @ VinceCheck out this thread:https://www.eevblog.com/forum/testgear/vintage-tek-restoration-pictures-by-martin/

author: Vince
author_rank: Super Contributor
timestamp: October 04, 2017, 06:45:03 pm
content: Wow, thanks for the link Tautech !!!A seasoned Tek restorer... and "local" to me as well, a German neighbor.Will take my time and read all 10 pages, but I can already see from the first page that he worked on two 310 models, these are very similar to my 317.With this thread and the guys at Tekscope, and this HV probe, my little 317 shall be fixed promptlyCan't wait to get started on the repair.

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2017, 06:53:59 pm
content: Quote from: Vince on October 04, 2017, 06:45:03 pmIt's all about remembering this sort of stuff is on the forum and being able to find it.If you get stuck with the 317 and have a thread going about it you can always PM Martin with a link to it and he'll likely come to your rescue.He knows a lot about glowing Teks.

author: Vince
author_rank: Super Contributor
timestamp: October 04, 2017, 07:11:34 pm
content: Yeah that's my intention as well ! Will try and do as much as I can by myself, and when I am really stuck or unsure about to do, I will bother those who do know their stuff

author: David Hess
author_rank: Super Contributor
timestamp: October 05, 2017, 03:47:15 am
content: I picked up a used Fluke 80K-6 inexpensively for working with oscilloscope CRTs but I was only interested in the cathode voltage which will be in the range of -2000 to -4000 volts.If you want to measure the PDA (post deflection acceleration) voltage, then a higher voltage probe will be necessary and if you want to measure some of the other high voltages, a probe with a higher input resistance will be necessary. Both are found in higher voltage probes like the Fluke 80K-40 which works up to 40 kilovolts and has a 1 gigohm input resistance instead of the 75 megohms of the Fluke 80K-6.With some experience, there is no reason to measure the PDA voltage because it can be diagnosed by how it affects the display. I have never had a reason to measure the other CRT voltages for the same reason.

author: Vince
author_rank: Super Contributor
timestamp: October 05, 2017, 11:43:34 am
content: Hi Dave,Thanks for your input.I am set on the 40kV one, will be more versatile and give the extra input impedance as you say.Buying a lower rated one would make sense if it could be had for 5 bucks delivered and all I wanted was to fix this 317 scope as cheaply as possible and call it a day...but this is not what I am trying to do. Fixing this scope is merely an excuse/opportunity to get a probe, but I am not trying to buy as low a spec as I can get away with. Rather I am trying to get something as versatile as possible for god knows what device or experiments I might fancy in the future.... and I don't see the point of buying sub 10kV probe only to be forced to buy a higher rated one later when I need to... and end up paying twice and having two probes taking up valuable space in the cramped lab rather than just one.So if a 40kV probe can do the job of a sub 10kV one, let's just buy that. And as you say, its higher impedance just makes it even more versatile/useful !

author: Vince
author_rank: Super Contributor
timestamp: October 06, 2017, 07:06:31 pm
content: Quote from: tautech on October 04, 2017, 06:11:24 pmTautech, Am only halfway reading that interesting thread, but then I got side tracked... there, there is a link to a sticky post about restoring old gear in general, how convenient, and then you gave yet another link, where people show off their Nixie tube gear ! Of course I had to look a t it.... 10+ pages, will take me quite some time to look at all this ! But I can't possibly miss on any of this stuff, so will have to read each and every post.... and maybe add my two own Nixie counter in there, if they have not been posted by someone else.This EEVBlog forum is incredibly large and resourceful ! I am glad people like you do remember where to find the interesting stuff... otherwise valuable information would useless because buried deep down and nobody would be able to find it. Search engines in forums never quite cut it IMHO... nothing beats well organized data like these sticky posts.Anyway, I am so excited at all this interesting and plentiful information, will spend most of my evening reading Martins thread and this Nixie tube thread.

author: tautech
author_rank: Super Contributor
timestamp: October 07, 2017, 12:24:15 am
content: Quote from: Vince on October 06, 2017, 07:06:31 pmI get just as much of a kick out of you enjoying those links as you do yourself.Rob.

author: Vince
author_rank: Super Contributor
timestamp: December 16, 2017, 03:15:55 am
content: Quote from: bd139 on October 03, 2017, 11:30:51 pmSome feedback after a a couple month, fo rthose who might come across this thread/ be interested in such a probe.Ended buying that 40kV Pintek probe, tried it when fixing the CRT section of my Tek 317, worked just fine, I am still alive. Overall build quality looks good, works just fine, stable reading. Quality of the leads and and clips is good, nothing looked cheap or crap or dangerous... it's a decent product, useful, very versatile with its 40kV range, and at a decent/reasonable price. Couldn't get it as cheap as BD139 did in the UK because I didn't find any unbranded HVP-40 when I searched, only OEM/Pintek branded ones, but still it was very reasonable and also came from the UK. somehow on the best price was there, not in China, go figure. I paid 75 Euros for it, including shipping to Frog land. I saw if for two or even three times that price though, so make sure to compare prices before buying !..... But at 75 Euros shipped, I feel it was quite a good buy, a useful and quality tool in the lab for not much money.Anyway,

author: cheeseit
author_rank: Regular Contributor
timestamp: June 19, 2018, 06:58:25 pm
content: Excellent, this thread was just what I needed. I was researching, and about to order, the Voltcraft H40 from Conrad (€114) and then found this thread. I'm pretty sure the H40 is a rebranded Pintek HVP-40 so I instead ordered the HVP-40 on eBay for €74 with free shipping from Netherlands. You guys just saved me €40, thanks! And thanks for the feedback Vince!

author: Vince
author_rank: Super Contributor
timestamp: June 19, 2018, 07:23:27 pm
content: No worries, glad this thread did not help just myself !And thanks to the guys above who led me to this probe, a great addition to my lab !