Real Scoop on meters for tube amp use

[tubedood]

Hi folks, just a quick question on grabbing a multimeter for tube amp use... I was told years ago by a tech in the Automation/Controls field that a simple analog meter would be my best friend in certain situations of needing fast reliable results in seeing a fast moving signal. He said it responds fast and accurate in ways a digital couldn't (at least back then in the 1990s). Do you folks still like the analog meters or are we going the way of the digital? I'm ok with either I do have a fluke for work but I'm curious if the analog still has its uses and preferences.

Thanks in advance,
Dale

[Leo_Gnardo]

I get it all done with an old Fluke benchtop DMM plus a couple of the better quality Radio Shack DMM's from 20-25 years ago. I broke or blew up all my ol' fashioned analog meters BUT sometimes they were handy. Somehow I'm getting along without analogs for a couple years now.

[tubedood]

Cool Leo thanks for the reply I appreciate it! I'm trying to get things together for a few amp builds and I'd like to be able to blame me this time for the failure and not the equipment haha

[bob p]

Most of the time you can get by with a DMM but be sure to check the specs. It's important to have one that has sufficiently high impedance that it won't corrupt your measurements. Although I use a DMM most of the time, there are instances where I'm glad that I own a VTVM.

[52 Bill]

Before digital meters were affordable, all we had were analog meters. I've had portable VOM's that didn't work well for tube amps and I still have my trusty old RCA VTVM.

I prefer the digital meters now, as they show me the voltage immediately. With the analog meter you have to interpret the values on the scales. Analog meters are cool when you are monitoring a fluctuating voltage, as the needle swings up and down with the voltage level. My current bench meter is digital, but it has a bar display that moves up and down with fluctuating voltages.

Whatever meter you choose, just make sure that it is rated to handle the voltage levels that you will be reading AC and DC, and that the probes are rated high enough as well.

[tubedood]

Thanks for the tips! I thought the old simpson analog was good for tube amp work but I'll have to research things further... things change!

[Leo_Gnardo]

Thanks for the tips! I thought the old simpson analog was good for tube amp work but I'll have to research things further... things change!

Yep the ol' Simpson 260 was the cat's pajamas at the time. They still make 'em too - figure on spending $275 to $500 depending on source & features, OW!

Mostly I used the analog meters to check transistor junctions, diodes too. Now there are diode & transistor checkers built into cheap DMM's.

As 52 Bill noted, fluctuating voltages will be hard to read on a DMM. Mostly I encounter this when repairing vibrato/tremolo circuits. When I see the voltage value bouncing around I figure something's starting to work right, then I hook up the oscilloscope to verify, and by that time I'm likely hearing wobbulation noise in the speaker = vibrato OK.

Somewhere I still have a Simpson 160 mini meter lurking around, should see what about reviving it. I think it takes a hinky battery, 22.5V, about the size of a regular AA, that's the hangup. Where to find one of those at a reasonable price.

[big_teee]

I haven't used anything analog meter wise in over 20 years.
I can use most DMMs, even the cheapies, the only pet peeve I have with some DMMs?
Are Meters that auto range, some seem to take forever to get there, to give a readout.
Some of the cheapies, you set the range on, and they actually read faster.
The other Item I've mentioned before, is if you pay a lot for a fancy meter, make sure it has auto power off.
I multi-task around the 20 acre property, and I'm bad about leaving meters, & soldering stations on.
The auto shutdown is a nice feature.
T

[Dave H]

I thought the old simpson analog was good for tube amp work but I'll have to research things further... things change!

Digital meters usually have a constant input resistance of 10M but the input resistance of an analog meter changes with the range setting. e.g. A 20k per volt (50uA movement) analog meter has an input resistance of 20M on the 1000V range but the input resistance is only 200k on the 10V range which isn't great if you want to measure grid voltage.

[Tom Phillips]

Digital meters usually have a constant input resistance of 10M but the input resistance of an analog meter changes with the range setting...

One needs to check the specs for every specific meter.
Comments:
A given DVM may have 10M input resistance on the DC ranges but it takes a fancy unit to provide more than 1M input Z on the AC range.
We need to distinguish between an old style analog VOM and the later generation electronic analog volt meters and older VTVM technology that maintained consistent input Z on all ranges. The presence of an analog meter face does not, in itself, indicate poor specs. However, the better last generation analog voltmeters were often specialized, high cost devices. They were directed at the laboratory market not the service bench. For someone that has the desire to put up with the extra setup and care of an old VTVM the performance to cost ratio is really good. All this equipment has its place.
Cheers,
Tom

[Dave H]

One needs to check the specs for every specific meter.

Thanks, I agree. I was only referring to simple analog meters as mentioned by the OP. I should have been more explicit.

[bob p]

^^^ Yes Tom -- there's just no (affordable) substitute for a VTVM.

Regarding the opinion that all good meters should have an auto-off feature, I'll take the other side of the argument --

All cheap DMM come with an auto-off function. The presence of auto-off on a meter isn't a sign of a quality meter.

While most all DMM come with auto-off features any serious meter should not have an auto-off function, or it should at least have the ability to disable the auto-off feature so that it doesn't get in the way of your work.

I don't multitask, I prefer to focus my attention on a single complex task. It's not uncommon for me to spend several hours at work without interruption. When designing it's not at all uncommon for me to have several oscilloscope channels and several meters all hooked up to monitor several parameters in real time.

Nothing in the world is as frustrating as having a meter decide to auto-off while you're in the middle of your measurements, all because some nitwit meter designer designed the countdown timer to begin it's countdown the last time that you twisted the multifunction knob. Any smart circuit designer would have designed the countdown timer to reset it's countdown the last time that the meter perceived a change in input. The result of this brain-dead design is that instead of turning off 5 mintues after you last took a measurement, these meters will turn off 5 minutes after you last twisted a knob.

I don't know about you guys, but I have an attention span that lasts more than 5 minutes, and I find a 5 minute auto off feature to be a great inconvenience. If you're using multiple meters concurrently on a task, and they all have an auto-off feature, your work flow gets interrupted while one meter after another decides to power down. The result is that while you're working, one meter after another starts chirping, and you have to interrupt your work to service a cheap meter's demand for a knob twist. I don't like test equipment that makes the job more complicated, and that's exactly what you get with cheap meters.

In the big scheme of things, I like scopes that have built in voltmeters, which allows the elimination of an extra meter and it's leads from the test setup. I like bench meters, because they don't have auto-off features that get in the way of taking measurements. I like handheld meters that don't have an auto-off feature, or have an auto-off feature that can be disabled.

I don't like having my work flow interrupted by a cheap meter that demands that I divert my attention to circumventing it's battery-saving design. Those meters are designed as if the battery is more valuable than the operator's time. Batteries are cheap. My time is not.

[Dave H]

Do you not like auto-off meters then bob?

[Justin Thomas]

I'm in the same boat with the auto-off. There are times when I really appreciate it, like when I forget to turn it off. Which is rare. But most of the time, I am trying to look for a rise in voltage over time, or some such related thing. 20 minutes (on mine) just may not be enough. Or I need to do some math after taking measurements, and that can sometimes take quite a while, at MY level... I find it very inconvenient to have to disconnect the meter from circuit, turn it off, turn it back on gain, then reconnect it to a live circuit... It's kind of a hassle, and I'd prefer to just set it and forget it.

That said, I just looked in my manual, and there <IS> a way to defeat the "battery saver" in my Fluke 112. Yay! If I remember to use it...

Justin

[big_teee]

Bob mainly just likes to try to discredit whatever I say or like.
That's fine!
My Fluke is the only meter I've had that has auto power off.
It is a great feature.
I never had much issue with any multimeter.
I usually find something I like and dislike about all of them.
All you can do with any meter is take measurements!
They usually either work or they don't!
T