[Test-Equipment] GR 1800A VTVM

[Richard Knoppow]

----- Original Message ----- 
From: "Barry" <n4buq at knology.net>
To: "Discussion of Electronic Test Equipment" 
<test-equipment at mailman.qth.net>
Sent: Tuesday, December 17, 2013 6:29 PM
Subject: [Test-Equipment] GR 1800A VTVM


> Anyone familiar with the GR 1800A?  I just got one and am 
> a bit baffled by the probe accessories.  The manual 
> displays them as they are disassembled and has a brief 
> discussion of them, but there aren't any diagrams showing 
> how they're supposed to be assembled.
>
> I think they're designed to form various configurations, 
> but I just don't see how they're supposed to fit together. 
> I can see that the banana plug unscrews from the center of 
> the probe and apparently one can replace the male plug 
> with the female adapter.  Other than that, I don't see how 
> the larger rings or the 50-ohm terminator fit together, 
> etc.
>
> Hopefully someone knows about these and can direct me a 
> bit.
>
> Thanks,
> Barry - N4BUQ

     I have two of them and both work well.  The probe has 
only a couple of accessories. One is a screw on attenuator 
for RF, another is a 50 ohm disc resistor.
     The probe has a collar around the front which is 
threaded in the center for the outer shell of a type 874 
coaxial connector.  There are three threaded holes around 
the periphery for small banana plugs, only one is used, as a 
ground connection. There is a similar threaded hole in the 
center of the probe also for a banana plug. When the 874 
shell is screwed in the banana plug acts as the center 
contact.  The multiplier just screws onto the end of the 
probe when the collar is removed.
    The 50 ohm resistor is mounted by removing the collar. 
You will find the resistor has a hole through the center, 
one side of the resistor is about flat and the other 
slightly recessed. The recessed end goes against the center 
of the probe and the banana plug goes in the hole. The 
collar is then screwed over the resistor and the 874 shell 
screwed on.  That gives you a 50 ohm termination that can be 
used to measure voltages on 50 ohm systems.
    I don't think there are any other accessories 
specifically for the probe, however, when the 874 shell is 
in place it can be used with all sorts of 874 accessories 
such as T connectors.
    There is one other accessory for the 1800A/B and that is 
a DC and low frequency multiplier. This has 274 terminals 
and banana plugs. It is normally used by plugging into the 
jacks on the front of the meter.
     I think there are handbooks in several places, try 
BAMA. The main difference (maybe the only one) between the A 
and B versions of the 1800 is that the B has a polarity 
reversing switch on the front. It is added to to the AC/DC 
switch.
    These are very useful meters. While it does not have the 
extremely high DC input resistance of the Hewlett-Packard 
410-B as normally connected it will approximate it when 
connected for open grid. The problem is that it must be 
zero-ed while connected to the source.  All this is in the 
handbook.
    BTW, I've found with both of mine that it was worth 
cleaning the contacts on both acorn tubes to improve the 
zero stability. Also clean the pins and contacts for the 
filament ballast tube. If you find the zero wanders around 
this is often the cause.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com