Bench Multimeter - Which one to get ? Fluke Agilent ?

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The Fluke 45 has dB measurement and "power" (watt) measurement for 2, 4, 8, 16 ohm.

Would it be good for measuring the output power of Tube amplifiers ?

As for the dB measurements, that seems like a good tool for measuring the roll off frequency and also for active crossover measurement.
What do you guys think about this ?
 
I have two Keithley 199 5.5-digit meters. They are great. They have true RMS AC with wide bandwidth (I measured 800 kHz at -3dB), 4-wire Ω, dB, and +-303000 count display. They actually report 6.5 digits over the GPIB bus. Mine both have the scanner option, so I can automatically or manually switch among 8 inputs. I picked one up very cheaply on eBay; the seller couldn't get a reading and listed it as "for parts/repair". Actually it didn't take readings because the trigger wasn't configured, and I had it taking good readings within a few button presses.

I would recommend getting one with LED or VFD display, not LCD. The readability of an LCD on a bench instrument is generally very poor since overhead lighting doesn't strike the display directly so contrast suffers (not usually a problem for handhelds). I can hardly believe that HP used them for so long on so many otherwise great instruments. Shame.

4-wire Ω isn't a big deal; you can use the zero feature with a 2-wire measurement to get results that are about as good. "Compensated" 4-wire is worth having, since it compensates for thermal/Kelvin voltages in the sense leads.

Keithley should be on your short list next to Agilent/HP and Fluke.
 
The Fluke 45 has dB measurement and "power" (watt) measurement for 2, 4, 8, 16 ohm.

Would it be good for measuring the output power of Tube amplifiers ?
Yes. You need to load the amp with a power resistor and then measure AC voltage accross it, after setting the reference value "4 Ohms" etc to the value of your load resistor plus selecting power for display.

As for the dB measurements, that seems like a good tool for measuring the roll off frequency and also for active crossover measurement.
What do you guys think about this ?
You can get freq. response data/graphing by using a sine generator and reading frequency and AC voltage in dB's at different frequencies. Then input that into an Excel spreadsheet and plot the results. You don't need dB value for this, normal voltage reading is OK, too, Just tell Excel to plot a logarithmic Y axis.

Using a soundcard and a (freeware) measurement software is much more convenient for audio frequencies, though. Active XO's a measured in the blink of an eye.
 
I recently picked up a very used Fluke 8840A/AA. Nice meter, but now I see the Fluke 45 looks even better for the typical hobbyist.
It does look like the 45 lacks 4-wire resistance measurement capability.

@manp111: If you are looking for an affordable, high precision instrument: I would want to support Stormrider on that statement.

The 8840A has excellent long drift specs and very good overall accuracy. Check for the AC true RMS option - but for the GPIB option only, if you are into it.

It is hard to get a better bench-top DMM bang for the buck in my humble opinion.
I have seen some FLUKE 8840As which were sold on ePay for less than 100USD incl. shipment. Ask for a picture of the VFD front display in operation, so you are not bidding for a dim one.

Cheers,

THDplusN_bad
 
It all depends on your requirements ...

Hi,

the Fluke 45 is nice due to its dual display.
The 8840A is different (and older) from the 8842A, but even beats it on long-term accuracy.
Both beat the Fluke 45 on accuracy, i.e. by a factor of 3 or more on DC voltage accuracy.

For typical repair and maintenance work on tube amplifiers, the accuracy of all three models would be more than sufficient I'd say.
Others might say they are all overkill anyway. ;)

A true advantage of FLUKE products is that you can download service manuals for most equipment from their website. Which is worth more to me than a fancy display or a brochure printed on glossy paper.

What is better for you depends on your personal preferences and what your requirements are.
I would study the technical specs which are all available on fluke.com and then decide...

Cheers,

THDplusN_bad
 
Another reason to choose LED... some Fluke LCD displays die prematurely. I bought a Fluke bench meter with a bad LCD display, and Fluke sold me a replacement for a reasonable amount. On some meters, the display can be saved by cleaning the conductive rubber strip with alcohol and/or flipping it end for end, which exposes fresh areas of contact material. A couple of coworkers and I bought Fluke 77's around the same time in the '80s; their displays failed within a few years; my 77 is still on the original display.

If you go for a used 88xx meter, be aware that while an 8810A appears to have switches and jacks for the ohm and AC V functions, those functions are not installed on the basic model, so the switches don't move (and break off if you try too hard). Presumably Fluke thought this would make it easier to upgrade, but it's annoying on the test bench and misleading when buying. There's a specification sticker on the underside with boxes to check off for the various options like AC, RMS, ohms, etc.
 
another vote for fluke 45. I have 2 of them.

they have rs232 on the back! for us automation guys, that is useful. no need to mess with complex hpib to get values into your computer.

bought my flukes on fleabay for $100 or less. they are findable at that price if you keep trying.

inside, they are very simple and very well designed (and stable over time).

I also have the bigger flukes (88xx series) but the 45 is just right for most people short of standards labs guys ;)
 
some of the older hp's and other brands will lose their calibration data if the battery on board is not changed in time. in fact, to change the battery means to lose calibration data! I have an HP that is like that, but my flukes store their data in eeprom (where it makes more sense than battery-backed ram!).

for people who don't want to be stuck with no calibration and forced to pay for that service after a battery failure, it can matter.

I've heard of people hot-plugging a new battery before removing the old (using blocking diodes). all just to keep their precious cal data ;)

just a thing to be aware of when picking an older ebay meter that is digital.
 
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