Real Scoop on meters for tube amp use

[Enzo]

I think I bought my first digital meter about 1974. In all that time I have never had a meter auto-off on me while using it. I will believe it happens, but I have never seen it.

Analog meter needles are "better" for seeing fleeting voltage changes. OK. If I really need to see something fleeting, I really ought to be viewing it with my scope anyway. My Fluke, and most modern meters have an analog bar on the display anyway. When i am watching a needle flutter, I am not looking at precise voltages, I am looking at trends and activities. The analog bar on my DMM does that just fine.

I got my first meter almost 60 years ago. it was of course analog. I still have my first Eico VTVM. As far as I know it still works, it sits across the shop. Haven't used it in years. Here is what I like about a digital meter. I can read 600v and then 6v and then -45v all on my DC scale without touching the meter. On my VTVM, if I read +600v and then probed -45v, I would likely bend the needle against the stops. I can adjust the meter to zero in the center on my analog, but then the scales are only half as long. But it does allow me to go both polarities.

If I inadvertantly probe 500v while still set for resistance, the meter objects on its display, but isn;t harmed.

My meter has a 10A current scale. None of my VTVMs had that. My VOMs did, but then they were not usually as helpful elsewhere.

I don't like to do it, but now and then my DMM hits the cement floor from the bench top. My VTVM would not survive that even once.

Don't get me wrong, those SImpson 260s are really fine meters, and if cared for will last a lifetime. Accurate, reliable, consistent. They were the standard of the industry for years and years for a reason. But I think that a good digital meter will do everything you need in an amp shop. I have a Triplett version very similar to teh Simpson, and now and then I get it out for nostalgia sake and think "I ought to start using this regularly", but I never do, because it serves no purpose to do so. If it were all I had, I'd do fine with it, but my Fluke suits my needs even better.

Plus the DMMs have useful tests like the diode test function. I use that all the time on semiconductors. I don't use it, but many meters now measure capacitance, even inductance, and hfe of transistors. Some even do frequency. Mostly those extra functions do not add to the cost.

[Tom Phillips]

Relevant points made by Enzo. An old VTVM is a nice blast from the past and can still be useful but it does not have the conveniences and protections built into modern test equipment. My original Heathkit VTVM sits on my office desk as a decoration and a memory piece that reminds me of my Dad when we built it together at the kitchen table in ~1963. It was my first piece of test equipment and I plan to keep it forever.
Cheers,
Tom

[Enzo]

Amen to keeping it. My second piece of gear was an Eico 950B cap bridge. I still get it out now and then to check cap leakage at high volts. A few months back, Dean stopped in for a visit and was eyeing it, and I almost sold it to him, but at the end of the day I just couldn;t part with it.

I had to convince my dad to let me buy the thing "You already have a tester, son, you don;t need two testers."

[The Dude]

I built a Heathkit meter in tech school (similar to the one pictured below). It sits at home as a "history piece". I couldn't tell you the last time I turned it on.

[tubedood]

So the general consensus is that the new digital meters can respond as quick as an analog for seeing a quickly changing signal?

[The Dude]

I would say that the analog meter has a slight advantage there (if you're looking to see a change). I use a scope for that, but if you don't have a scope.......

[tubedood]

Cool Dude that's what I was wondering... Maybe a cheapo 10 or 20mhz scope is my next purchase! I'd love to learn to see whats actually going on in these amps.

[Enzo]

I guess the question is just what would be the situation wherein you would need to see fast changing voltages on a meter? No one would propose using a DMM as a VU meter. How often does it come up? And for every situation where you might prefer a needle moving, there will be a hundred places a nice stable number staring out at you is better. If I measure B+ on a tube amp, it will be about 500v. If it moves about as the mains drift, so it changes from 498 to 503 and back. My DMM will show that, and I can;t imagine why I'd need to know exactly when and how fast it made those tiny changes.

An analog meter movement has momentum, it is not instant. it can swing fairly rapidly, but nowhere near as fast as say an LED VU string. The analog bar on a modern meter is pretty quick itself.

The most basic scope you can find will be enough to work on these amps. Your audio bandwidth is not a challenge to any scope. We all prefer triggered sweep, and I doubt anyone even makes recurrent sweep scopes these days anyway, but if you find a working old non-triggered scope, like many basic Heathkits and Eicos of 50 years ago, it still will display what you need on the screen. The difference between triggered and not triggered is a triggered scope will display a steady signal like a sine wave rock steady, while a basic recurrent sweep scope you may have to fiddle with the sweep to get it steady. if you are off a bit, it slowly walks across the screen. But even moving, it is fine for looking at ripple or at a waveform.

[The Dude]

Yes, I completely agree. Although I did say that the analog meter would probably be more useful for monitoring more rapid voltage changes. I also said in post #19 that I haven't fired up mine for quite some time (years). So, I wouldn't say the need for it comes up often.

Edit: Years ago, I repaired and aligned satellite equipment. It required making calibration adjustments wherein you would adjust a pot or variable cap for maximum voltage at test point "x". It was much easier to find the peak adjustment with an analog meter. Since then and now that I work primarily on audio gear, I haven't had much use for that meter. The point is, I guess, that it depends on what you intend to do with it.

[tubedood]

Thanks Enzo for the reply! The main reasons I needed a fast responding meter was for duty cycle and sensor input and I think your right Its not needed in this situation so a decent digital is ok? (OH my I'm clinging to our roots haahaa I miss the analog meter)...

[Enzo]

Well, you will never see duty cycle on a meter. You could peak it as an RMS response I suppose, but that is where a scope comes in - duty cycle.

Look at it this way, invest in a good DMM< and then one day if you REALLY need an analog for something, plop down a few bucks for a working VTVM and add it to your collection. No reason to be either or. Just most everyone will tell you how nice it is their analog meter, but they haven;t gotten it out in years.

[bob p]

Bob mainly just likes to try to discredit whatever I say or like.

It's not that way at all, Terry. Sometimes I just have an opinion that doesn't align with yours. You need to be ok with that.

[bob p]

Well, you will never see duty cycle on a meter. ....

Never say never. Maybe you've got such a well-stocked bench that you haven't been shopping for meters in a while, but today's meter-on-a-chip packages commonly provide a duty cycle function in even the cheap bargain-bin class of meters. (Of course, whether or not it actually does anything useful is an entirely different question.)

this Cman meter is probably 15 years old and has a duty cycle setting that I don't even use. Fluke even offers online instructions on how to use it's meters to measure duty cycle.

How to measure duty cycle with a digital multimeter

[bob p]

I built a Heathkit meter in tech school (similar to the one pictured below). It sits at home as a "history piece". I couldn't tell you the last time I turned it on.

LMAO. I have one of those Heath bench-type VTVM in beige!

[bob p]

I think I bought my first digital meter about 1974. In all that time I have never had a meter auto-off on me while using it. I will believe it happens, but I have never seen it.

I guess whether or not you've ever been annoyed by an auto-off feature would depend a lot on how you use your meters. My understanding is that you primarily do service work, where your bread and butter is to diagnose a problem, fix the UUT, and get it off of the bench as quickly as possible. If I had your diagnostic acumen, I would probably never see a meter auto-off on me. But to say that I don't have your level of repair experience would be a great understatement.

I think that the likelihood of being annoyed by an auto-off function is a lot more likely if you're a hobbyist builder, a modder, or a designer. I imagine that someone like Justin gets frustrated by auto-off because the meter can shut down on him while he's in the middle of diagnosing a problem, crunching a few numbers, and thinking about what he wants to change. I don't doubt that if he just wanted to ID a bad part, replace it and move on, then he wouldn't have that problem. But repairing and modding are entirely different tasks.

Someone like Chuck, who did a lot of voltage testing developing his zener mod thingy, probably looked at a UUT long enough to allow an auto-off meter to shut down.

This week I have been trying to reverse engineer an amp that has a horrible frequency response problem. I don't have a frequency response sweep plotter, so I had to do my plot the old-fashioned way -- spin the dials and push buttons on the frequency generator, write down the output voltage onto a notepad, repeat. by the time I swept the UUT for all of the relevant data points on a double log dB plot, the meters had shut themselves off a dozen times.

whether or not auto-off is a problem for the user depends entirely on what type of work he's doing. i think that someone who focuses on repairs, or just builds amps off of schematics, is likely to not ever experience the frustrations that someone might gripe about when doing design work or blueprinting a circuit. I think it all depends on the type of task you're performing.