EICO 232 VTVM

2/4/2002 4:05:47 PMDave

I was recently given an EICO 232 VTVM in good condition,
minus the probe. Is there anything special about the
probe used (resistance?) or will any test lead suffice?
I want to replace the selenium rectifier before I power
it up; can anyone suggest an equivalent silcon bridge rectifier
or diode combination to use? I have downloaded the
manual and service bulletin from this site and can
begin refurbishment/calibration when I get this info.
TIA

2/4/2002 8:29:43 PMDean Huster

The DC probe of nearly every VTVM in existance has a 1M ohm, 1/2-watt resistor in series with the test lead inside the probe. The AC/ohms probe has no resistor and is just straight-through with the wire. If the probe is a switchable "Uniprobe" that handles the AC/DC/ohms measurements, this 1M ohm resistor is switched in and out with a switch on the side of the probe. That's why the input resistance of the "common" VTVM is 10M ohms on AC and 11M ohms on DC.

Dean

2/5/2002 2:43:42 PMGreg

: The DC probe of nearly every VTVM in existance has a 1M ohm, 1/2-watt resistor in series with the test lead inside the probe.
: Dean

Dean,

When making a replacement probe it would be a lot easier (from a construction stand point) to place the 1 Meg resistor inside VTVM at the selector switch. Is there any real advantage to having the resistor in the probe?

Greg

2/6/2002 9:35:26 PMAlan Douglas

: When making a replacement probe it would be a lot easier (from a construction stand point) to place the 1 Meg resistor inside VTVM at the selector switch. Is there any real advantage to having the resistor in the probe?

Yes, absolutely: it isolates the probe capacitance from any RF circuitry you're measuring. John F. Rider got a patent on that idea.

2/5/2002 10:03:34 AMJohn McPherson

Hi,

The rectifier can be replaced with a single silicon diode with a PIV of at least 200 volts, and 1 amp. I usually use 1N4003's. Digi-key has been a good source for them in the past.

If by chance you have a full wave unit,it will have 4 terminals, either use 4 of the above, or use a bridge rectifier of the same parameters as the single diode above.

: I was recently given an EICO 232 VTVM in good condition,
: minus the probe. Is there anything special about the
: probe used (resistance?) or will any test lead suffice?
: I want to replace the selenium rectifier before I power
: it up; can anyone suggest an equivalent silcon bridge rectifier
: or diode combination to use? I have downloaded the
: manual and service bulletin from this site and can
: begin refurbishment/calibration when I get this info.
: TIA