[volt-nuts] Fluke differential meters

[GandalfG8 at aol.com]

Hi Robert
 
Your comments reminded me that some years ago I bought a Fluke differential 
 voltmeter and a hernia inducing struggle through other equipment to reach  
it down from a shelf just confirmed it's an 893A.
 
I must admit I was more interested in the case when I bought it, sacrilege  
I know but at least it looked too nice to take apart so did remain intact,  
and I'm much more inclined now to leave it that way:-)
 
Component markings suggest this one dates from around 1984 and it  uses the 
same style blue plastic switch wafers in the Kelvin-Varley divider  that 
later became notorious for failing on the Redifon 551 HF receiver.
There are, or were, some references on line to repairing the switches  in 
the 551 and I have seen the wafers offered for sale from time to time, I seem 
 to recall they were also used in one version of the RS components  
"make-a-switch" kit.
As far as I can tell from the manual though and unless I'm missing  
something, which isn't entirely unkown:-), the voltage reference  consists of a 
pair of zener diodes rather than a Weston cell.
 
Either way, I've just discovered one of the switches is jammed, the wafers  
look ok and I don't recall it being jammed when I bought it so not sure why 
 yet, but there goes what I already had planned for today:-)
 
Regards
 
Nigel
GM8PZR
 
 
 
In a message dated 07/08/2013 07:37:44 GMT Daylight Time,  
robert8rpi at yahoo.co.uk writes:

Hi  Joe,
The 893 is worth having as a working instrument. The older ones are  
collectibles (possibly) or a source of parts. The Voltage reference is a  Weston 
cell which will be well past it's expected life. In particular  these meters 
have a Kelvin Varley voltage divider. This can be used  without the meter 
section working, possibly recased. The plastic switch  dials/drums do tend to 
crack or warp due to srinkage of the plastic though. If  theK-V dividers 
switches are worn out, they are still a good source for  precision matched 
resistors. Perhaps not spot on value but all the  resistors in a decade will be 
very close in value. These can be used for  voltage dividers and Hamon 
resistor units (google Hamon resistor and see  
http://conradhoffman.com/HamonResistor.html  ). They may not look much  but are high performance. There are 
other precision resitors in these  units Take care when removing them, don't 
apply any force or stress to  the resistor body as this can affect
their performance.

Robert  G8RPI.


________________________________
From: Joseph Gray  <jgray at zianet.com>
To: Discussion of precise voltage measurement  <volt-nuts at febo.com> 
Sent: Wednesday, 7 August 2013,  6:00
Subject: [volt-nuts] Fluke differential meters


The local  surplus guy has at least three different differential meters that
have been  collecting dust for decades. I have borrowed two of them (so 
far).

The  first one is a Fluke 893A and is solid state. Although it appears to
work,  it fails the very first of the performance tests. Now that I have a
full  manual, I'm going to look at this a bit closer.

The second one is a  Fluke 803B (I think. There is no label on it). It has
tubes. I am slowly  bringing it up on a variac before messing with it. I
plan to open it up  later and take a good look.

I'm not sure what the third model is, but  it looks like it may be an even
older Fluke. It is on a high shelf and I  haven't gone over there to lift it
down yet. I'll probably do that later  this week.

At the moment, I'm just playing around with this gear and  learning a few
things. In the long run, are these things worth  having?

Joe  Gray
W5JG
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