Re: HP34702A Ohms converter issues
FN2960 sounds like and old Fairchild part number, They used a ceramic body with a drop of epoxy, or molded plastic cases. They used their trademark, a styleized 'F' as part of the part number.
Michael A. Terrell
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-----Original Message-----
From: gregdunn@...
I put a pair of 2N3904 in for Q13-14 - no change unfortunately. :-(
Yes, it's hard to figure out what Q11 needs to be - HP lists 'FN2960' as an equivalent but that doesn't come back with a match for any part. It has been recommended to me that I use a PN4117 which I have placed an order for but it hasn't arrived yet. I stuck in a NTE466 as a quick test, and it did seem to help on the lower ranges but not the highest two. The 466 does have a much higher Vgs rating, though, so that might be a concern. It did test as back-to-back diodes, though, whereas the original Q11 just showed "unknown part" or open depending on what I used to test it. Being a JFET, that's plausible.
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Re: HP34702A Ohms converter issues
George,
Thanks so much for chiming in!? As an engineer, my fellows and I had the utmost respect for what HP's designers were able to accomplish and getting info straight from the source is a rare treat.? I will require a little time to digest your comments, but I will try to understand and process the info as soon as I can before trying more tests on the unit.? For some reason this one was much less intuitive than fixing the 3490A I just finished, but I will soldier on.
Orin,
I'm sure you're right - the NTE part, lame though it is, was all I could get my hands on at the time, so I figured it was worth a toss.? I can't find the 4118 but I'll try to match its parameters and see what is closest. When the 'proper' part comes in I'll give it another try just for completeness.
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Re: HP34702A Ohms converter issues
The NTE part has max value for Vgs(off) of -10V.
NSN?5961-00-615-7002 shows?part numbers including FN2960 and 1855-0412. ? It has '3.0 maximum gate to source voltage' which I assume is the same parameter.
I don't think you stand much chance with the NTE part. ?2N/PN4117 has max Vgs(off) of -1.8V and will likely work. ?2N4118 would be closer with -3V max.
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Hi Tim,
Nice. Interesting that it is that accurate at 4GHz after the conversion. I have more than several of these generators and I think they are great.
I noticed on mine that if you do a hard reset (I don't recommend that unless you can't do anything else) that, regardless of model, that they default to 4GHz until you go below the models frequency and then won't go back up.
These are not high end generators but good enough and you can't beat the price for what you get.
Tom
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On 2/12/2019 1:11 AM, Tim Tuck wrote: Hi Tom,
At 4GHz, using my E4406 to measure its output from -90dBm to +13dBm, it appears to be within 0.5dBm of indicated.
Above 13dBm the power doesn't increase and the UNLEVELED indicator comes on at about 14dBm.
Using my HP438A and HP8481H to do the same test gives a similar result but with an additional -1dB offset.
So its "close" :) ... well at least at 4Ghz
None of this kit has been calibrated in years so take the result with a grain of salt!
Given a bit of time I could write a labview thing to make some nice measurements and plots some graphs
regards
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Re: HP34702A Ohms converter issues
That's weird - I thought I saw another response to this thread but when I refreshed the page, it disappeared!? :-(
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Re: HP34702A Ohms converter issues
I put a pair of 2N3904 in for Q13-14 - no change unfortunately.? :-(
Yes, it's hard to figure out what Q11 needs to be - HP lists 'FN2960' as an equivalent but that doesn't come back with a match for any part.? It has been recommended to me that I use a PN4117 which I have placed an order for but it hasn't arrived yet.? I stuck in a NTE466 as a quick test, and it did seem to help on the lower ranges but not the highest two.? The 466 does have a much higher Vgs rating, though, so that might be a concern.? It did test as back-to-back diodes, though, whereas the original Q11 just showed "unknown part" or open depending on what I used to test it.? Being a JFET, that's plausible.
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Re: HP34702A Ohms converter issues
I was just looking back at the schematic and OP - I see that you reported Q11 was bad and replaced, but not with the same type. This could be the problem, since JFETs all work more or less the same, but can vary greatly in characteristics. Check the Idss spec of your replacement versus the original type. It could be that Q11 simply can't cut off far enough with the available negative gate drive from U2. If you don't have the right one, or one close enough, you can help it out a bit by adding a shunt resistor from the gate to -12V, to drop the gate more, then U2 can lift off the rail and get control of the situation. Another option is to temporarily add a diode or two in the source lead to lift it, and help cut off. You should put the same or a proper equivalent part in once it's figured out.
Ed
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Re: HP34702A Ohms converter issues
If U2 is railed negative, then Q11 should cut off. Are the parts in sockets? If so, try pulling Q13, which should drop the gain and the current to a very low value. If there's no effect, then try Q14. If Q13 or Q14 are bad, the current will be out of control. These two are exposed to the outside world in ohms range, so could have been damaged by over-voltaging, even though the Q12 circuitry is supposed to protect them somewhat (SOA-wise, but not much beyond Vcbo). They should both be fairly high Vcbo types (I'd guess 2N3440 or similar - an HP favorite), able to withstand momentary? specified fault conditions. They may test OK at low voltage, but if Q13 in particular is leaky, it could throw the current way off. For testing and diagnosis, you can replace them both with ordinary NPNs like 2N3904, then put the right ones in after you figure it out.
Also, you may want to recheck Q11 to be sure it's OK, and the of right type. It's easy to quick-check with a DMM - the D-S should look like a resistance with no gate connection, and the gate to D or S should look like a diode.
Ed
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Prologix has updated the EZGPIB file and is working on the C++ example.
The title says it all.
You will find many examples in the folder when you download it.
Just click on EZGPIB.exe to run.
Investigate the?DF6JB Plotter as well.
No affiliation, I just like this software because it works.
PeterB?
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Re: HP34702A Ohms converter issues
> I think we're getting close to the "Aha !" moment !!!
I hope so.? ;-)
In this setup (Q12 / CR13 out of circuit), the gates of Q15 are offset just a bit - A: -5.0V B: -5.8V? The drains are of course then far apart - A: 2.8V B: 8.46V? and the sources are tied together at -4.9V.
This means the inputs to U2 are both way off from the quiescent value of 5.7V.? U2 is not quite at the rail, but close: -10.9V and there's no drop across R43.
This should be trying to reduce the current from the current source by turning off the FET/darlington circuit, right?? Yet it isn't.? I can't quite believe that the replacement Q11 is also defective, but maybe...
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Re: HP34702A Ohms converter issues
The problem is obviously revolving around the op-amp which is made up of Q15 and U2.
The two gates of Q15 should be balanced at all times, otherwise the output of U2 would be stuck at the +12 or the -12V supplies (because U2 is supposed to have infinite gain).
So you could do this: in a situation where the two gates of Q15 are NOT balanced, look at the output voltage of U2, does it saturate ? What are its two input voltages ?
Does it control the output current ? Are you seeing any voltage drop across R43 (in series with U2's output) ?
I think we're getting close to the "Aha !" moment !!!
Joel
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Pat,
Thanks. I was pretty sure David had the A/B designations swapped, but confirmation greatly appreciated. And it would be very easy for someone reading the thread later to get things backwards with unhappy consequences.
Reg
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Re: Interested in helping start/run a Wiltron/Anritsu group on groups.io?
Might take a few hours to be approved and propagate.
On Tue, Feb 12, 2019 at 2:50 PM bownes via Groups.Io <bownes= [email protected]> wrote:
On Tue, Feb 12, 2019 at 2:08 PM David Feldman via Groups.Io <wb0gaz= [email protected]> wrote: Looking for person (one or more) interested in starting and running a Wiltron/Anritsu equipment group (possibly modeled after this HP-Agilent-Keysight-equipment group) on .
If you are interested in (or knowledgeable about) doing this via , please contact off-list. If you're aware of such a list (I could not find one), please let me know.
Thank you
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Re: Interested in helping start/run a Wiltron/Anritsu group on groups.io?
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On Tue, Feb 12, 2019 at 2:08 PM David Feldman via Groups.Io <wb0gaz= [email protected]> wrote: Looking for person (one or more) interested in starting and running a Wiltron/Anritsu equipment group (possibly modeled after this HP-Agilent-Keysight-equipment group) on .
If you are interested in (or knowledgeable about) doing this via , please contact off-list. If you're aware of such a list (I could not find one), please let me know.
Thank you
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Re: HP34702A Ohms converter issues
With the protection circuitry disabled, the 1K resistor reads 1.87K. U3's inputs are both at -6.4V.? Its output is at -7.4V. Q15 seems to depend on what I'm measuring; for this test, its inputs are at A:-5.5V B:-6.4V.? I was getting a fair match yesterday when testing the output current.? There is still a 1.9V drop across R55-R56. U2 pin 6 (its output) is at -10.9V now.? U2 and U3 outputs are both quite clean with the 1K resistor on the unit's inputs:  
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Interested in helping start/run a Wiltron/Anritsu group on groups.io?
Looking for person (one or more) interested in starting and running a Wiltron/Anritsu equipment group (possibly modeled after this HP-Agilent-Keysight-equipment group) on groups.io.
If you are interested in (or knowledgeable about) doing this via groups.io, please contact off-list. If you're aware of such a list (I could not find one), please let me know.
Thank you
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On 2/12/19 12:36 PM, Eric Garner wrote: In regard to the collet extractor for APC-7, where did you find one
cheap? I've been looking high and low for an inexpensive collet
extractor without success. I bought mine from Globaltest a few years ago, I think I paid about $40 for it. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
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Dave,?
In regard to the collet extractor for APC-7, where did you find one cheap? I've been looking high and low for an inexpensive collet extractor without success.
-Eric
On Mon, Feb 11, 2019 at 9:00 PM Dr. David Kirkby from Kirkby Microwave Ltd < drkirkby@...> wrote: On Tue, 12 Feb 2019, 04:04 Reginald Beardsley via Groups.Io <pulaskite= [email protected] wrote:
One question I have is how difficult is replacing the N connectors? on a 8753B with an external test set if they are worn out.? Part of what I'm trying to do is is acquire a self sustainable bench.? I want to have tools to fix things.? I can't do anything about the problem of sourcing parts? ?But first of all you have to have the tools to identify the fault.? I've done it with "flint knives and stone axes'" but that is *very* tedious.
To my knowledge all 50 ohm 3 GHz test sets (85046B) have APC7 connectors, not N connectors. If the test set has N connectors then it is almost certainly an 85046A which is a 75 ohm test set, and best avoided.?
Changing the connectors on the test set is unlikely to be practical without changing the complete bridge, although the collets in APC7 connectors can be easily changed if you get a collet extractor, which you could pick up cheaply. It is most unlikely the APC7 connectors are worn out. Most people put APC7 to N adapters and so the APC7 connectors are rarely used.?
Dave.?
-- --Eric
_________________________________________
Eric Garner
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Re: Test fixture for dielectric measurements
Chris Trask - N7ZWY/WDX3HLB
Hmmm... If solid, you could hold the material in air away from the electrodes
Connecting to the material is a problem, especially above 1000 deg C.
Metals may react with fumes and change or melt. Many insulators and
dielectrics certainly will.
We are watching these exchanges with great interest.
Chris Trask N7ZWY / WDX3HLB Senior Member IEEE
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Just going through my old emails. You may find the attached useful. Don't even think about getting into the bridge to change the impedance. HP uses stripline on a saphire substrate (on the 85046A anyway) and the 75 ohm is a different dimension. PeterB
On Tue, Feb 5, 2019 at 1:55 PM Steve Hendrix < SteveHx@...> wrote:
A fellow engineer raised a question re the 75 ohm
characteristic impedance of the HP8714ET I just purchased off eBay.
Although I have minimum-loss matching pads ordered and enroute, does
anyone here know just what would be involved if I were to open up the
unit and try to change the impedance with some part swaps? The firmware
already supports a choice of 75 ohm or 50 ohms as the impedance, for
Smith charts, etc. I suspect that before I do that, I had better get the
service manuals, but that's for the future - thus far I'm less than 1/4
of the way thru reading the user manual, and I have a bunch of other
documentation to read as well. I'm very pleased with my purchase, if only
for the education I'm getting!
Steve Hendrix
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Michael A. Terrell
bownes
Dave McGuire