[Test-Equipment] GR 1800A VTVM

[Barry]

Richard,

Okay.  That helps a lot.  I didn't realize those were used to form 874 connectors.

I'm still a bit puzzled, though, as there are two threaded "adapters" that can be screwed into the collar.  One is slightly longer than the other.  Inside one of them (I think its the shorter of the two), there is a knurled sleeve that slips into the adapter.  While both threaded adapters appear to be identical except for their lengths, this knurled sleeve only slides into one of them.  The other one's I.D. is too small to allow the knurled section to slip into it the way it does the other one (but only by a few thousandths of an inch or so).

Is one supposed to be used with the male banana plug and the other with the female banana socket (so as to fit either gender of an 874)?

Also, inside the top of mine, there is a round wooden block that holds these accessories.  At the 12:00 position, there is what appears to be a nut with an internal thread that is the same size as the threads on the banana plugs.  Is this just meant to be a keeper for the 50-ohm disc and I'm just missing the screw that holds it in place?

Thanks again,
Barry - N4BUQ

----- Original Message -----
> From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
> To: "Discussion of Electronic Test Equipment" <test-equipment at mailman.qth.net>
> Sent: Tuesday, December 17, 2013 10:02:42 PM
> Subject: Re: [Test-Equipment] GR 1800A VTVM
> 
> 
> ----- 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
> 
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