Tube voltmeter vs typical multimeter

[001]

Hi

Is tube voltmeter has any benefits vs typical modern multimeter? (I mean DMM produced 1990-2000)

[TimFox]

The main advantage of a VTVM over a modern DMM is the 1 megohm resistor in the probe.  This isolates the reactance of the probe cable or wires from the point being measured.  This is important for higher impedance nodes that may have AC voltage on them, such as an un-bypassed cathode in a tube amplifier.  The reactance of the probe cable can affect the high-frequency performance:  in worst case, that could cause oscillation and shift the DC voltage greatly.  This is not important when looking at a point with only DC, such as the power rails.
I have never seen such a probe resistor on a digital device, but one can be improvised easily (this will change the voltage calibration, but the math is easy).

[Ringmodulator]

Hi,

my opinion:

There are some instances, like alignment of an HF transceiver, where an analogue instrument is preferable.
Jumping numbers on a DMM can be quite anoying.

The other question then would be VTVM (Vacuum Tbe Volt Meter) vs. conventional analogue multimeter.
The VTVMs were popular because of their high input impedance in relation to the earlier generation passive multimeters with lower input impedance.
Masuring in high impedance circuits with a low impedance meter gives you misleading readings and present a burden to the DUT.

Analogue multimeters with an active high impedance input made the passive ones obsolete.
In this respect, they are as usable as the VTVMs.

VTVMs are rumoured to be more robust, but I think that this is questionable.

Regards
Chris
 

[vk6zgo]

Such things as the HP 410C use an RF probe for the ac range.

Although I say "RF" probe, its frequency range reaches from 20Hz to 700Mhz.
http://www.hparchive.com/Manuals/HP-410C-Manual-sn-311-328-339-433-532-550-807.pdf

In contrast, a typical DMM's ac response falls off after a few 10s of kHz.
There is a workaround, however, as you can make an RF probe to use with your DMM.
These have been described many times on the Internet.

[TimFox]

The 410 series has a special RF/AC probe with a high frequency diode for AC voltage measurements, and a DC voltage probe with a 10 megohm resistor (110 megohm total resistance) for DC measurements.