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 Post subject: Probe for HP 4815A Vector Impedance Meter
PostPosted: Feb Sat 27, 2010 2:51 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 4075
Location: Long Island
Anybody have a lead on where to find one, in any condition?

This is a fairly complicated gadget, has current and voltage sensing transformers, several transistors, and diodes packed inside it. HP never actually published all the details of its construction (manual says 'not field serviceable') and they stopped supporting it about 25 years ago. Needless to say, the meter doesn't do anything except collect dust without a probe.

There have been some things on The Internets about people trying to make their own, but I haven't found anything that's complete or doesn't involve hopelessly butchering the meter. Any thoughts would be welcome.

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 Post subject:
PostPosted: Feb Sat 27, 2010 5:13 pm 
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Joined: Feb Wed 25, 2009 4:06 pm
Posts: 987
Location: Morristown, N.J.
Those probes are damned near impossible to get. The last person to have any was an HP authorized rebuilder/seller who is retired in SC. I know he has none available while demand is huge.

It's an extremely complex device and no one has ever actually made a substitute that met the original specs.

Many of the parameters that the 4815 measured can be read with a relatively inexpensive MFJ 459 (?).

The mainframe 4815 makes a very nice, clean, stable signal generator that can be AM modulated with an external mixer- been there, done that.

Pete AI2V


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 Post subject:
PostPosted: Feb Sat 27, 2010 8:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2703
Location: Monterey California USA
Why oh why do people always have to separate the probes and other removable pieces from test gear? The bane of the surplus buyer.

Somewhere orbiting a planet far away must be thousands of special probes, front covers, rear covers, cabinet lids, shock mounts, nameplates, one-of-a-kind IC's, service manuals, unique connectors, special switches, SP-600 cabinets, tunnel diodes, tapped pots, and more...

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 Post subject:
PostPosted: Feb Sat 27, 2010 9:01 pm 
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Joined: Feb Sun 17, 2008 11:36 pm
Posts: 1551
Location: Dayton, Ohio
Geoff Fors wrote:
Why oh why do people always have to separate the probes and other removable pieces from test gear? The bane of the surplus buyer.

Somewhere orbiting a planet far away must be thousands of special probes, front covers, rear covers, cabinet lids, shock mounts, nameplates, one-of-a-kind IC's, service manuals, unique connectors, special switches, SP-600 cabinets, tunnel diodes, tapped pots, and more...


A salesman/technician at Fair Radio showed me a stack of new-in-box General Microwave power meters, all with-out the sensor mounts :(

Don't forget to include gallium arsenide diodes (disconnect diodes) in that orbit, and I USED to commonly see knobs for BC-348's, new and un-painted, at the local surplus store, but no more :(

Charlie


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 Post subject:
PostPosted: Feb Sat 27, 2010 10:41 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 4075
Location: Long Island
I am not sure exactly what happened with the HP 4815A probes. One would think that every new meter had a probe, but almost never do you see a 4815A with its probe for sale together today.

Certainly some of this is due to the "equipment on this pallet, cables in that hamper" kind of thing that happens when a facility is dismantled, but one would think that the scrap dealers would be on the look-out for bits and pieces like this that are literally worth their weight in gold to somebody who needs them. My guess is there might have been something about the original design that did not hold up too well, so many of the probes might have been trashed at an early age and the meters just lingered in storage areas until they too got dumped.

Looking at the circuit in the manual, it appears that building a replica probe might be within reach of a well equipped electronics lab. Certainly with modern ferrites and surface mount components, construction ought to be easier today than it was in 1968. The big challenge is keeping the impedances in line over a span of 500 kHz to 108 MHz!

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 Post subject:
PostPosted: Feb Sun 28, 2010 6:51 am 
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Joined: Feb Sun 17, 2008 11:36 pm
Posts: 1551
Location: Dayton, Ohio
Sometimes a dishonest DRMO manager will pass parts of equipment and manuals, to "friends". Although equipment "turned in" by the military, is not supposed to be cannibalized, knobs, manuals or hardware, are not listed on the turn-in tags, sometimes get pulled for good and not so good, reasons.

Charlie


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 Post subject:
PostPosted: Feb Sun 28, 2010 7:03 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16550
Location: Somers, CT
Ever wonder how someone hooked up a HP 8443A tracking generator to the spectrum analyzer??? They all seem to be missing a 8W8 sub-D coax cable assembly that costs $150 to replace. There must be a heaven where these parts go to.

Pete


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 Post subject:
PostPosted: Feb Sun 28, 2010 8:38 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Athens, Greece
Pete, on that subject, I'm making a trip home in early April and will look in my junkbox for those connectors you need. If I have 'em they're yours.


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 Post subject:
PostPosted: Feb Sun 28, 2010 3:46 pm 
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Sounds good to me, JN!

Pete


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 Post subject:
PostPosted: Mar Wed 03, 2010 10:26 am 
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Joined: Feb Tue 23, 2010 10:41 am
Posts: 85
Location: Valencia - SPAIN
Hi Pete,

Peter Bertini wrote:
Ever wonder how someone hooked up a HP 8443A tracking generator to the spectrum analyzer??? They all seem to be missing a 8W8 sub-D coax cable assembly that costs $150 to replace. There must be a heaven where these parts go to.

Pete


Well, it seems I was extremely lucky then, as my HP-8443 came with an original HP cable :D (as did the 8444 and 8445)

On a sidenote, I was very happy with my nixie type 8443. It was so silent... no fans... no fans ???. One day I opened it to find there was a cable preventing fan to rotate!. I had it for about 10 years and had never opened it :shock: . So now it is cooler... but noisier!. This unit came from a military depot facility so it was probably cleaned and stored with the jammed cable on it.

Regards,

JOSE

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 Post subject:
PostPosted: Mar Wed 03, 2010 1:36 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 149
Jose, I had the same experience with a Nixie 8443A. In mine the fan was stuck all by itself. A drop of oil got it rotating again. Now I use a fanless 8443A with LEDs.

Pete, I made my own 8443A cable with parts from Mouser. This was several years ago, but I think they are still available. If you go this route, don't neglect the fourth cable (or was it the third?) that enables the front panel "restore signal" function. I had bought extra connector pins so I was able to add it when I realized that the older schematic I built my cable from was incomplete.

Brian


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