Budget Multimeter for Vacuum Tube Use? - Page 1
Forum section: electronics / beginners

author: Ungolian
author_rank: Regular Contributor
timestamp: February 10, 2021, 09:26:10 pm
content: Hello all, first post. I'm an enthusiastic hobbyist, and I've put together my fist lab. I do audio work exclusively (mostly guitar), mainly 9v audio circuits, but have a few amplifiers I'd like to play around with. The amps are smaller combos, with plate voltages around 350VDC or less. I have an oscilloscope, an Owon VDS1022i (purposely got the "i" model), and use it with my laptop (battery only mode). For signal generator, I use my phone or tablet, and a frequency generator app. For now I only need a 1k sine @150mv (approximates a guitar input signal), and it seems to work fine.My question is what to do about my DMM choice. I have a Mastech MS8222h, but it's doing an odd thing where it's showing a constant -0.5v (that doesn't translate to a linear -0.5v drop when measuring) no matter what I do- different batteries, 9v adapter powered, and I calibrated it properly (100mv, the fine tune pot does nothing). I also have a Mastech MS8268 which works fine. Having 2 meters to read voltage and current is what I'm after, and I've scoured the forums already for the price range I'm looking for. It's the usual suspects- Aneng 870 (and it's re-branded brothers), Uni-T UT61E, Holdpeak HP770d, Vichy, Fluke 101, Amprobe AM-510, AstroAi 6000, etc. But they all have some particulars that make me question them, whether it be long-term reliability, input protection (I'm probably right on the edge of it being a factor), not true RMS (which I want), or if I should deal with Banggood/Ali. Without turning this into a discussion about what's already been covered, are there any other brands/models I've missed? I mainly need voltage and current functions, accuracy isn't SUPER important, portability is important (ruled out some used bench models, need to diagnose on site sometimes). Any sleepers? Anything I've listed "Good enough"?Apologies if this is covered somewhere else, but all I saw about tubes and meters was someone talking about a couple of bench meters they used for this stuff. That's not practical for me.Thanks!

author: bdunham7
author_rank: Super Contributor
timestamp: February 10, 2021, 10:22:49 pm
content: Since you like Mastech, look at the AMES DM1000 from Harbor Freight.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 10, 2021, 10:31:37 pm
content: Welcome to the the forum(s).You will get a lot of opinions and recommendations here. FWIW, about 20 years ago I bought my first piece of test equipment specifically for work with audio amplifier vacuum tubes. My mentor recommended a Fluke 179 and I have never regretted the choice. I think the key reason behind the recommendation was the ability to safely and reliably count on the Fluke to handle high voltage. It turns out that for some electronics measurements there are other meters that offer some advantages - especially for lower level signals but for safety and reliability it's hard to beat a Fluke. You might also consider some Brymen models but for high voltage I wouldn't cut any corners. Once you have one very good (very safe) meter you can always use other budget constrained meters for less demanding measurements. If Flukes are out of the budget the Brymen's are easy choices - they probably offer more value than the Flukes. Check out Dave's new EEVblog branded (Brymen inside) 786. It offers a lot for a very good price.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 10, 2021, 10:38:41 pm
content: Quote from: bdunham7 on February 10, 2021, 10:22:49 pmThis looks good.https://www.harborfreight.com/DM1000-Electricians-HVAC-Contractor-TRMS-Multimeter-64019.htmlIf Joe Smith blesses it as safeit could be a very good value.

author: Ungolian
author_rank: Regular Contributor
timestamp: February 10, 2021, 10:46:40 pm
content: Thanks to both of you. The Ames CAT ratings seems a little beefier, which is a plus (if true). $50 on eBay. Not particularly attached to Mastech, that's just how it worked out (I got the 8268 for like $25). I like the looks and features of the Aneng, but there is enough questions to make me a little hesitant. I did look at Dave's meters, and would love to have a Fluke. But right now, having to replace a broken meter is an unexpected (and unnecessary) expense. Especially now, budget is important. Even when testing plate voltages, I just do a quick check to see what it is, no prolonged contact. Usually it's just measuring bias on already working amps. Anyone else? Bueller...? Bueller...?

author: bob91343
author_rank: Super Contributor
timestamp: February 10, 2021, 11:21:48 pm
content: Save a little and give up on true rms. It's of very little value for the most part. What prompts you to specify that? I have both true rms and untrue, and have never had a need to worry about true rms. In fact I am scratching my figurative head to think of a situation where that would be important, especially for your situation.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 10, 2021, 11:26:17 pm
content: If that Harbor Freight DM1000 meter is this Mastech MS8215B meter:http://www.mastech-group.com/products.php?cate=123&PNo=144.... for $70 it looks like a worthy contender, especially if Joe S blesses itEven if something on eBay looked similar, I'd pay $20 more to get Joe's good housekeeping seal of approval if I was going to run 300+ volts through it. If Joe isn't testing it, I guess you could roll the dice and get the $50 version - but Ames could put their name on anyone's product. I'd go for an Ames product that looked like it might be the Mastech MS8215B.

author: Ungolian
author_rank: Regular Contributor
timestamp: February 10, 2021, 11:47:13 pm
content: It's not so much that I need RMS for anything I'm doing, it's a matter of adding something else to my toolbox, which can be useful in the future. It looks like the Ames has Lo Z input, the Mastech is probably Hi Z (the manual wasn't helpful). I like that too. I like collecting stuff I don't currently have. I got this transistor tester a couple of months ago, and I've used it more than anything. I have a bunch of vintage transistors I got a long time ago (OC44's, OC75's, BC108's, and BC109's).

author: Electro Fan
author_rank: Super Contributor
timestamp: February 10, 2021, 11:59:51 pm
content: Quote from: Ungolian on February 10, 2021, 11:47:13 pmYou are fitting in very well here.(I'm still voting for the Harbor Freight that looks like it's a Mastech MS8215B.)Edit:https://manuals.harborfreight.com/manuals/64000-64999/64019.pdfLooks like it has Lo-Zhttp://www.mastech-group.com/products.php?cate=123&PNo=144#_Scroll down to the Support tab to see the manual for the 8251B; it has Lo-Z (page 11)HF Ames DM1000 and Mastech MS8251B look to be very similar.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 11, 2021, 12:26:00 am
content: One of the comments says this is based on the Mastech MS8251.Edit: Pretty good candid review but I think I'd see if some other forum members who are familiar with the 8251 recommend it for probing high voltage DUTs. Otherwise it might be worth considering Brymen (or Fluke, etc.).

author: bob91343
author_rank: Super Contributor
timestamp: February 11, 2021, 01:58:03 am
content: What is low-z? That's a new one on me.

author: bdunham7
author_rank: Super Contributor
timestamp: February 11, 2021, 02:03:43 am
content: Quote from: bob91343 on February 11, 2021, 01:58:03 amCommon feature found on electrician-oriented meters nowadays, it uses a lower resistance PTC across the inputs to load the circuit slightly and eliminate stray voltage caused by leakage and capacitive coupling. This meter has a somewhat lame Low-Z, a 400K resistor apparently. Fluke typically uses a PTC with a 3-4K normal resistance that increases if any real voltage shows up. I don't know what other manufacturers do.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 11, 2021, 02:29:12 am
content: Quote from: bob91343 on February 11, 2021, 01:58:03 amGood question. When I saw your post I figured I might have been researching/reading/copying and pasting too fast or had a dyslexia moment or two. But check out the images from the Mastech and Ames manuals.

author: bdunham7
author_rank: Super Contributor
timestamp: February 11, 2021, 02:30:58 am
content: Quote from: Electro Fan on February 11, 2021, 12:26:00 amThe OP wanted TRMS and stuff and wanted it cheap. The other green Cen-Tech meter for the same price looks interesting--it measures sound level, light level and relative humidity??? But no TRMS.Anyway, one downside to any of these meters is that they generally are not properly protected against accidental overloads in non-voltage ranges. If the OP is measuring a 400VDC plate voltage but mistakenly leaves the meter in a resistance range, he may fry it on the spot. I'm not sure how they get away with the CAT rating and ETL Intertek approval, but I don't have the standards so I can't say.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 11, 2021, 02:38:41 am
content: Quote from: bdunham7 on February 11, 2021, 02:30:58 amRogerHard to get everything plus inexpensive. My main thought is that when working with high voltage sufficient user protection and equipment margin for error is the first requirement.

author: bob91343
author_rank: Super Contributor
timestamp: February 11, 2021, 03:24:06 am
content: I don't think it's wise to equip a lab with a lot of stuff at the outset. Unless you know exactly what you need.My approach has simply been to wait for bargains. I go to swap meets (at least I used to) and comb the auction listings and make friends with people of similar interests. I trade and I bargain and in the process meet some cool guys.It took a while but now my lab is beyond my previous dreams. I have precise gear, wide bandwidth, great tools, and I have invested very little. In the process I have accumulated a priceless body of knowledge.I have gotten stuff that needed repair and often I could repair it. Again, the knowledge and experience are priceless.Sure you can buy your way into a fancy setup but considering the cost and lack of knowing what you are buying, I think that's not the best way.I have been doing electronics now for maybe 75 years, or more, and never have needed a true rms meter. I have never needed a low-z one either although cobbling up one doesn't appear to require a rocket scientist. I work from audio to vhf and if someone needs a measurement I usually can do it.Just a few words for a kind of reality check.

author: Ungolian
author_rank: Regular Contributor
timestamp: February 11, 2021, 04:54:24 am
content: Quote from: bob91343 on February 11, 2021, 03:24:06 am

author: Ungolian
author_rank: Regular Contributor
timestamp: February 11, 2021, 04:56:19 am
content: Edit error...Thank you all for the replies so far. Lots of good info. The Ames/8215b has my interest, it seems a little different than the normal meter. The HVAC marketing angle seems like a good mid point- It's not entry level, but it's not engineering grade. Bob, I appreciate the advice too. I'm a little past the beginning stage, and there are some things I can see in the somewhat immediate future, and having tools that can get me in the right ballpark is definitely useful. Whatever those needs are.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 11, 2021, 05:17:51 am
content: Quote from: bob91343 on February 11, 2021, 03:24:06 amAll the voice of experience and wisdom, for sure.Just one possibly slightly different view regarding RMS.(And it looks like Ungolian is past the beginning stage so this is probably not applicable to the OP, but it might have some merit for beginners.)It has been my experience that working with RMS can sometimes help the "non-highly math adept" start to see some patterns, or cause an enthusiast to wonder what drives the patterns, such as 0.707, 1.414, 2.828. When sine waves are at work (which is often the case with function generators and in other situations), non-highly math adept enthusiasts can do testing and measuring and see the patterns at work and maybe start to do the math that shows the relationships as the concepts of peak and peak to peak and RMS are observed. Of course sine waves are not always the case, perhaps as most often and clearly seen when wall AC is involved, so RMS doesn't solve all problems. And of course if someone is strong with calculus the area under the curve can be determined regardless of the shape of the curve. But as people start from scratch with electricity, electronics, and test equipment and as they try to get their head around DC vs AC and volts vs amps vs watts and as they learn the applicable math from scratch (often starting with Ohm's Law) gaining an understanding of RMS can be pretty helpful. And therefore, at least for beginners, it's probably good to have at least one meter (or maybe two) that can measure RMS - if for no other reason than to stimulate thinking regarding why two meters (one that does RMS and one that doesn't) will show two different measurements of the same signal.

author: Ungolian
author_rank: Regular Contributor
timestamp: February 11, 2021, 06:07:30 am
content: I'm always willing to learn. In fact, here's a question or two. Most of the stuff I deal with are some type of audio amplifier (guitar, bass, PA, gain boosting effect). They all have a hi Z input, low Z input, or both. Is there a preferred difference between using a hi z meter with a low z input, and vice versa? Is it that each circuit (meter and amplifier) has its own impedance, usually set by the input stage of each circuit, and each meter makes it calculations based on its input z, not the input Z of the audio circuit? Does it really matter? Second, I really wanted a true RMS meter for a second source of comparison, a different set of measurements. Unnecessary? Probably. Over compensating? Most likely. Also, I can use my scope for a lot of measurements. It's an Owon VDS1022i. It's rated high enough, is isolated, has 2 channels, and is portable enough (it fits in the same case as my laptop). Ideally, I want a PicoScope 4262 for audio range, and the Owon doesn't seem like a bad choice for higher voltage/risk stuff (it was fairly cheap).

author: helius
author_rank: Super Contributor
timestamp: February 11, 2021, 06:18:43 am
content: Quote from: Ungolian on February 10, 2021, 11:47:13 pm"Lo Z" is useful in exactly one circumstance, and that is testing for live circuits in fixed electrical wiring. In all other situations you want as high an input impedance as possible to avoid loading the circuit under test (especiallyin vacuum tube circuits which have high impedances everywhere). Lo Z is mainly found in meters designed for electricians.

author: helius
author_rank: Super Contributor
timestamp: February 11, 2021, 07:05:58 am
content: Quote from: Electro Fan on February 11, 2021, 05:17:51 amAllmeters (and I do mean all) will read the magnitude of an sinusoidal AC waveform in volts or amps RMS. RMS is not "optional". It is the way the amplitude of sinusoids isdefined.There is no (useful) "non RMS" measurement of the amplitude of a sinusoid. You can measure the peak-to-peak (P-P) voltage on an oscilloscope or a scope-meter hybrid like the Fluke 289; P-P is not the amplitude. On other meters like the Fluke 189, you can display either the positive or negative peak: again not the amplitude. Only the RMS of an AC waveform is its amplitude.What is different betweenTrue RMSand "average responding, RMS indicating" (the only other common type of meter)?Response to non-sinusoidal signals only. The first type reports the RMS amplitude of the signal; the second type assumes the signal is sinusoidal, integrates the average of the absolute value of the signal, and scales its reading based on the sinusoid assumption. So a square wave's amplitude will be indicated with a +11% error: the average of the absolute value of the square wave is equal to its peak, and is equal to its RMS, but since the meter assumed sinusoids only, it multiplies the average of the absolute value by 1.11 to get the "sine"'s RMS, even though the waveform was not a sine wave. The square wave case is the one with the greatest error: all other waveforms yield lesser errors.https://www.eevblog.com/forum/beginners/what-is-the-differance-between-mean-value-response-and-rms/QuoteThere are no meters that "don't do RMS". Full Stop. See above.If the readings on two meters with and withoutTrue RMSdiffer, it means the waveform isnot a sinusoid.

author: Ungolian
author_rank: Regular Contributor
timestamp: February 11, 2021, 08:09:01 am
content: Thanks for the input Helius. I think I'm just over complicating things for myself. Seems like the scope can answer that question better than the meter, if needed I haven't had a scope that long.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 11, 2021, 08:32:16 am
content: Quote from: helius on February 11, 2021, 07:05:58 amSorry for the improper terminology of “do”. Of course any meter will produce a reading, but as you point out the reading might differ by approximately 10% with some meters. In some situations a user might or might not be aware, or care. In some situations it might matter. Full stop.

author: bdunham7
author_rank: Super Contributor
timestamp: February 11, 2021, 03:11:01 pm
content: Quote from: Ungolian on February 11, 2021, 06:07:30 amLo-Z on a DMM is not related to the different input impedances of amplifiers. The basic idea is the same, but they exist for entirely different reasons. I don't know if you are confusing the frequency symbol (Hz) with Hi-Z or what, but handheld DMMs typically don't have any type of Hi-Z option. And when you talk of making calculations, I assume you mean the reference impedance of a DMM that measures dBM or has some other decibel function--that is yet another concept. In that mode, the actual impedance of the meter remains unchanged but you tell it (or on some it just assumes 600R) what the assumed impedance of the circuit is, from that it can calculate dBm from voltage. Anyway, you have 3 entirely different issues there, best not to mix them up.QuoteIf you are budget constrained, TRMS might be a feature to consider dropping. If you are measuring anything other than mains power derived AC, like audio signals, you need consider the DMM frequency limits. Many DMMs have very low frequency response in the AC ranges.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 11, 2021, 05:04:29 pm
content: For audio, I would perhaps consider a meter taking into consideration one additional aspect: bandwidth. If you would like to have a good idea about the response of an audio amplifier across its operational range (up to 20kHz), it might be interesting to have a meter that can reach that. Most of the options shown are electricians' meters and go up to a maximum of 3 or 4kHz.The cheapest option I know that can reach this bandwidth is the UT61E - unfortunately it is not the most robust out there. Other meters start to get above the $100 mark, such as the Brymen BM857/BM867 (20kHz).Being in the United States, you may also try to find a good deal on Fluke's wonderful 8060A - although an old one, it reaches 100kHz and its specs are impressive even to this day. But that suggestion comes with the normal warnings for a used equipment.In my opinion you already have a good collection of instruments for what you do - even for higher voltages of your vaccuum tube amplifiers, as long as you are paying attention to what you do. Of course, as bdunham7 also says below, the Mastech meters you have may not survive a distraction, but you will still be dealing with much lower energy than the limits of any CAT I circuit.Quote from: bdunham7 on February 11, 2021, 02:30:58 amThe CAT ratings do not care about the instrument's survivability, but how well it stays together on an event.One aspect about joeqsmith's tests is that they deal with multi-kVtransients- events that happen in the tens of milisseconds which you will rarely (if ever) experience debugging an amplifier. As mentioned before, chances are that you will eventually forget the meter on a specific range and leave it plugged for several seconds before realizing your mistake. Joe's tests give an idea about the outcome of such scenario but are not definitive in any way. For that, you can look at one of the early Dave's videos where he plugs the meter in an outlet and goes through the ranges - pedigree meters such as Fluke, Keysight, Brymen... or even others such as Klein, for example.

author: Ungolian
author_rank: Regular Contributor
timestamp: February 11, 2021, 10:21:55 pm
content: Thanks to all that have contributed. I'm just going to save up a little more and get one of Dave's BM235s, very reasonable considering what you get. Getting a second meter immediately isn't necessary. After looking at so many meters over the last couple of days, it occurred to me that a lot of them kind of have a Star Trek kind of look to them...

author: wizard69
author_rank: Super Contributor
timestamp: February 13, 2021, 01:21:22 am
content: Quote from: Ungolian on February 10, 2021, 10:46:40 pmIf the budget is tight put off the purchase! I personally believe meter safety is important no matter what you are doing. The higher the potential energy in the device you are working on the more important it becomes. Even transistor based amps can produce some nasty surprises so the fact that you have tube circuits doesn't make the problem that much more significant. So putting off until you can pay for a slightly higher end meter makes sense to me.I also like Dave's new EEVBlog meter and might even buy one as soon as taxes are handled. Otherwise I tend to go with Fluke for handhelds. However just because I have Fluke on my mind doesn't mean there are not cheaper choices out there. The main reason to go with the EEVBlog meter is to support the forum and get something back that I can actually use.

author: wizard69
author_rank: Super Contributor
timestamp: February 13, 2021, 01:55:30 am
content: Quote from: Ungolian on February 11, 2021, 10:21:55 pmI see what you mean. If there is one place that Fluke comes up short it is on fancy displays! It occurred to me that considering the meters you already have you might want a meter with rudimentary scope functionality. That really blows your budget but if you are willing to wait even longer that might not be a problem. A chips become cheaper scope meters have come down in price so it may be worth seeing what is available at the time you make your purchase decision. Such devices do well with audio work as you don't need massive bandwidth and of late have become more capable. That may make your field work a lot nicer too. I'm not thinking A high end Fluke here but rather something like > Vhttps://www.amazon.com/dp/B078WRKZG7/ref=sspa_dk_detail_2?psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFUTTZaUTZROE1RUzYmZW5jcnlwdGVkSWQ9QTAzNDc2NTExWFdDWVQ5RlVaSE8wJmVuY3J5cHRlZEFkSWQ9QTEwMjc3MDBLQk1DN0I0VE5YVUQmd2lkZ2V0TmFtZT1zcF9kZXRhaWwyJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==I have no idea what the quality is like on this unit, it is just an example of what popped up. Eventually somebody will get the UI and the performance right such that such a meter will be very useful. Some of the older examples sucked from the usability standpoint. Oh i didn't check the voltage range on this unit and frankly BNC connectors suck for high voltage safety. I bring this up because there are time where such a feature would have saved me some grief. Contrast this with a lot of the special functions or features in a meter which seldom get used.I'd almost suggest buy a Fluke Scopemeter but I can't afford one and I suspect you can't either. I'm just keeping an eye on these alternatives as one day there will be a $200-300 meter that actually works well and is of high enough quality to purchase.

author: Ungolian
author_rank: Regular Contributor
timestamp: February 13, 2021, 07:17:13 pm
content: I do have a scope, an Owon VDS1022i. I did a lot of research before I bought it, and it seems like a hand-down winner for what I'm doing. It's portable (a necessity), it's isolated (I use it with my laptop in battery only mode), and it's rated at 400v peak to peak, I really didn't see anything even close to that, and certainly not in that price range. Now is that rating accurate? Can't say. There is a good EEVBlog thread on it too, with the general consensus that it is a great scope, for the money. Better/more sensible construction than comparable Hanteks. That's the other reason I can wait a little longer on getting another meter. I haven't had a scope for too long, and I generally look to grab a meter when I really don't need to- I have a scope!Also, I didn't know who this Joe Smith guy was (I just saw the name thrown around a couple of times in this post), but wow! He's like Mythbusters for this type of stuff. Mad props! I wouldn't mind seeing him take on some of these budget USB/PC scopes.Can anyone confirm or debunk the ratings on my scope?

author: rsjsouza
author_rank: Super Contributor
timestamp: February 13, 2021, 07:54:29 pm
content: I have a VDS1022I as well and really like it, but I haven't tested its maximum input of 400Vpk.However, I looked at its USB isolation circuit and it is quite good due to the isolation switching converter IC device being used (and there are no stupidities in the PCB routing).I think that you come across as someone making very solid considerations before a capital expense and I agree that, with what you have, reaching for a more robust and solid meter is a good move. Good luck in your quest for your next meter!

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 14, 2021, 06:30:59 pm
content: Forgive me for jumping in so late, but I just noticed the thread title and it startled me.I don't think "budget multimeter" and "vacuum tube use" belong in the same sentence, much less on the same workbench. You need a good quality meter with actual real insulation that can handle over 400 volts routinely, and probe leads and probe connector tips to match (like alligator clip tips and grabber tips, because you will want to clip the negative multimeter lead to the chassis of your DUT or some other location in the circuit, and probe the circuit with one probe in one hand only). In this regard I care less about what it says on a CAT label; I care more about brand names, sturdy build quality, field reputation, and of course it has to have the CAT rating.All of which, for me, adds up to Fluke. Shop used markets if necessary but remember: cheap tools are no bargain.(I have an ancient 83 for mobile use that is still going strong, and an 87-III that I use around the bench at home.)

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 14, 2021, 07:53:10 pm
content: The previous post has a really good point. It is hard to beat a Fluke for high volt safety.Also note that the voltage measurements you will obtain with a modern multimeter will not match the volts on any old schematic.The volts on old tube schematics were not made with modern Multimeters which are more like a VTVM.The really good old multimeters, like VTVMs, had several different input impedances.Also the previous post had another good point, there is a saying that old electronics techs had one hand in their pocket while measuring volts to avoid a shock while new techs have one hand on the ground (chassis) to avoid static charge to any chip..You may also wish to consider an old analog unit but be careful of the old test leads etc...

author: TimFox
author_rank: Super Contributor
timestamp: February 14, 2021, 09:00:23 pm
content: To WG: VOMs in the vacuum-tube era were simple voltmeters, with a switchable resistance in series with a sensitive ammeter. The cheapest were "1000 ohms/volt", with a 1 mA meter; better were "20,000 ohms/volt", with a 50 uA meter (e.g., Simpson 260), and the expensive ones were "100,000 ohms/volt", with a delicate 10 uA meter. The schematic diagram in the service information would specify which rating was used when measuring voltages, or possibly if a 11 megohm VTVM (see below) was used. The effect of a 1000 ohms/volt meter on the circuit voltage would be substantial.To Helius:One must be careful about emphatic use of "all", as in "All meters (and I do mean all) will read the magnitude of an sinusoidal AC waveform in volts or amps RMS. RMS is not "optional". It is the way the amplitude of sinusoids is defined."It is true that average-responding and true-RMS responding meters are always calibrated in terms of RMS values of the waveform, and that average-responding meters will only give the correct answer for a sine wave.However, back in the vacuum-tube days, many normal VTVMs used apeak-to-peakresponding rectifier circuit, and the meter would have separate calibrations for RMS (valid for a sine wave) and peak-to-peak (which would be accurate for a wide range of waveforms).Another detail about vacuum-tube circuits, especially RF and other wide-band applications (maybe not so important for audio circuits): since VTVMs were often used in radio repair, where touching a normal voltmeter lead (including those supplied with modern DVMs) would disturb a high-impedance node with excessive capacitance, it was normal to include a 1 megohm resistor near the tip in the probe used (only) for DC volts, to isolate the capacitance of the cable and voltmeter from the node. For example, measuring the DC voltage on the plate of an IF amplifier, or the DC grid voltage.My -hp- 410A, with 110 megohm input impedance, had 10 megohm in the probe, but the more common RCA VTVMs (and competition) had 11 megohm input impedance with 1 megohm in the probe. One can obtain the equivalent effect with a modern DVM by adding a resistor in the probe body, with a coaxial cable to the DVM, and correcting the reading for the voltage ratio (e.g., 10/11).

author: Ungolian
author_rank: Regular Contributor
timestamp: February 14, 2021, 10:22:13 pm
content: Is one of the EEVblog Brymens not in the same category as a Fluke safety-wise? I've been watching a lot of the Joe Smith You Tube vids, and the BM235 seems to get his "thumbs up". Second, my initial question was looking more for a meter that wasn't necessarily in the "trendy" category (Uni-T, Aneng, etc.), and has issues that make them questionable for this kind of stuff, but more for a manufacturer that cut corners in the accuracy category, and had decent protection and legit CAT ratings. Literally every meter I looked at in the beginning seemed to be great on accuracy, questionable on safety. I'm not dealing with Arduino, getting voltage and current readings that are in the ballpark are acceptable (previous comments about original analog MMs seem to back that up). Electro Fan pointed me in the direction of an Ames DMM, aimed at HVAC, which seemed to be exactly what I was looking to find. But since I also have a scope with a fairly beefy 400v peak-to-peak, so I can do pretty much everything I need with it while I save up for a Dave-O-Meter.

author: bdunham7
author_rank: Super Contributor
timestamp: February 15, 2021, 03:13:15 am
content: Quote from: Ungolian on February 14, 2021, 10:22:13 pmThere are many good reasons to buy Fluke, but the safety issue is way overblown, IMO. It isn't Fluke vs everything else, it is reputable manufacturers that use independent testing labs vs manufacturers that skip or lie about actual testing and safety performance. The Brymen 786 has a higher CAT rating than the Fluke 117 meter that is specifically for electricians, so it is probably good enough. I wouldn't worry about it. If you buy some cheap crap on Aliexpress, then you should worry about it.QuoteI really recommend you not use it at those levels without a better probe.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 15, 2021, 03:16:17 am
content: I think if safety is #1 you can’t go wrong with an appropriate Fluke model, but based on the many threads here and as reinforced by Joe Smith you can very likely say the same about Brymen. Study those two and find the models that best fit your requirements and budget. If some other manufacturer has something that looks attractive vs your favorite Fluke and Brymen add it to the short list. My guess is you will be safe and happy with a Fluke and you will be safe and happy and some $ wealthier with a Brymen.

author: Ungolian
author_rank: Regular Contributor
timestamp: February 15, 2021, 05:47:30 am
content: I'm pretty much sold that the Brymen is the way to go. But just wanted to hear it from people more experienced than I am (some of you should get kickbacks from Dave...).Honestly, I've never had more than 50vdc on my scope yet. I'm using it in the preamp sections of tube amplifiers, or 9-18vdc audio circuits. But a better set of probes isn't such a bad idea. If I'm diagnosing something and it isn't powering on, I'll check the fuse(es), and I'll do a quick check around the power transformer and rectifier with a meter. I've never used a scope for that, and I've never dealt with anything over 350vdc. There are some old Selmer and Marshall (particularly the Marshall Major 200w) amps that had plate voltages upwards of 600vdc, but I'll never see one of those. If there's anything wrong with a KT-88, there really isn't much a scope or meter will tell me that tapping on it with a pencil won't...

author: wizard69
author_rank: Super Contributor
timestamp: February 15, 2021, 06:45:31 am
content: Quote from: Ungolian on February 15, 2021, 05:47:30 amWell if Dave has a meter that fits the application it is a good way to support the forums. Every little bit helps and Dave is listing the units for a good price.In any event; if there is a situation where high energy is possible then you really want to buy a respected meter. That is one reason I often suggest Fluke as I'm a long time user in industry. There are of course others beyond Fluke such as HPAK, Brymen and others but I've not used any of those handhelds extensively.