[Boatanchors] Novice questions on buying a suitable meter for boatanchor work

[Garey Barrell]

Dennis  -

1)  Yes.  The only additional feature would be 'True RMS' but that increases the cost considerably, 
and is not needed very often.

2)  Most DMMs are 10 Megohm input impedance on all voltage ranges.

3)  Definitely a short-coming of a digital meter.  It will drive you crazy.  Most quality meters 
(including the Fluke 115) have a 'bar graph' across the bottom of the display screen.  This helps 
somewhat, but still no comparison to an analog needle.

You might want to keep your eyes open for a Heathkit VTVM, IM-11/13/18/28/...  They're all the same 
circuit, main difference is meter size.  You can find a nice one for $10 - 20 in good shape, and a 
good 12AU7 will last forever.  Be sure and get the switchable 'DC/AC-Ohms' probe with it.  Aside 
from the nice analog meter, they also have a 1M resistor at the tip of the probe that serves to 
disconnect the test probe cable from any high impedance voltage readings such as the grids of 
oscillators, mixers, etc.  The plain DMM probe will kill the oscillations.

One last thing.  Do NOT apply more than the rated maximum voltage to a DMM.  It WILL smoke it, at 
best a very difficult to procure internal fuse, at worst a damaged PC board.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>


R. Dennis Gibbs wrote:
> All,
>
>
>
> My last analog volt-ohms-milliamp meter (VOM) has finally died.  It's been
> over 30 years since I purchased a test meter, and they have certainly
> changed a lot in that time!
>
>
>
> I'm looking (hoping?) to spend less than $200.  I have no real idea *what*
> to buy, or if I can even buy anything decent in that price range.  I have my
> eye on a Fluke 115 DMM.  I can get it from Digikey for about $167.95.  In
> addition to volts, ohms, and current, it also measures capacitance, which I
> figure will be useful.  My novice questions are:
>
>
>
> 1)      IS this a reasonable choice for boatanchor work?
>
> 2)      What about input impedance for sensitive circuits?  I remember they
> used to rate analog VOMs at up to about 100K ohms per volt, and VTVMs at
> around 2 Megohms per volt, with the latter being more suitable for taking
> measurements without affecting operation of the circuit under test.  But, I
> see no ratings like this on the DMMs I've been looking at.  Is this no
> longer an issue with DMMs?  Can this be used much like the old VTVMs were
> used?
>
> 3)      One of the things I loved about the old analog meters is it was
> great for "Peaking" circuits when doing alignments.  With digital readout, I
> suspect it will be harder to do this.  Is there anything about the new DMMs
> that make it easier to use in this fashion?
>
>
>
> I'm hoping to make a quick purchase on this, as I can't continue with my
> projects until I have a usable meter!  I don't really have time to search
> for a vintage meter that would be suitable.
>