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

[Jim Wilhite]

I have always been partial to the RCA 98 series of VTVMs.  However it is 
difficult to find one today that has not suffered from battery leakage 
or other types of abuse.

So before you invest in a VTVM of that age, take a look inside for 
corrosion or other problems.  The last version of the 98 series RCA put 
the battery at the top.  When the owner retired it the battery was left 
in the compartment and leaks all down the main board and covers the 
calibration pots.

Another choice is an analog meter with an FET input.  If you can find 
one they are good as well, just don't buy a pig in a poke.

Jim/W5JO

----- Original Message ----- 

> 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.
>