Standalone Tek 7000 series plugins? - Page 1
Forum section: electronics / testgear

author: MarkL
author_rank: Unknown
timestamp: April 30, 2015, 10:25:49 pm
content: Has anyone tried to use any of the Tek 7000 scope plugins in a standalone application? Some of them look useful and are available for cheap, but I don't want to start investing money and space in 7000 series chassis boat anchors.At the moment I'm interested in the 7A13 differential comparator and amplifier. The specs on this are not too far off from its pricey modern-day descendant, the LeCroy DA1855A.After looking at the schematics for the 7A13 and a representative chassis (I picked the 7704), I don't see a reason why it couldn't be done. I think all that's needed is a power supply with +/-50V (tracking), +/-15V (tracking), +5V, and a second +5V for the lights.For the output I would need to convert the differential vertical output to single-ended so I could feed it to a modern digital scope. Any low-noise, fast op-amp should do. For the 7A13 something on the order of 150MHz would probably be more than enough.Besides the power input and vertical output, all the other edge connector signals I don't think are needed. Most of them appear to communicate the plugin's settings for display purposes. (One caveat is that plugins other than the 7A13 might need other signaling, and maybe faster differential to single-ended conversion, but that could be for later.)Does a standalone chassis or something similar already exist?7000-series fans are probably already familiar with the 7A13. For the unfamiliar but curious, here is the the user/service manual:http://bama.edebris.com/download/tek/7a13/tek-7a13_late.pdf

author: soren
author_rank: Regular Contributor
timestamp: April 30, 2015, 10:55:35 pm
content: Quote from: MarkL on April 30, 2015, 10:25:49 pmhttp://w140.com/tekwiki/wiki/NT-7000

author: MarkL
author_rank: Unknown
timestamp: April 30, 2015, 11:24:38 pm
content: Ah ha - thanks! That would be it. The picture even has the 7A13 plugins.Finding one may prove to be a bit difficult. No signs of any for sale, or have been sold recently.I might end up building something anyway while waiting.

author: Rupunzell
author_rank: Frequent Contributor
timestamp: May 01, 2015, 06:45:45 am
content: Why not simply use the 7A13 in a 7000 mainframe and take the vertical signal from the signal out BNC on the front panel?The output can be scaled and routed to a DSO. Check the BW of the signal out as they vary from 7000 main frame to 7000 main frame.Or simply use the 7000 main from for the measurement required?BerniceQuote from: MarkL on April 30, 2015, 11:24:38 pm

author: dom0
author_rank: Super Contributor
timestamp: May 01, 2015, 07:29:33 am
content: Quote from: MarkL on April 30, 2015, 11:24:38 pmOne sold a few weeks ago for 300-something Euros. I don't think anyone has a manual for the NT-7000, but the mainframe manuals list the PSU requirements anyway. Differential to single-ended conversion could be done with a CFA at high bandwidths, but CMRR would be rather poor. Not sure if that matters, though.edit:http://www.ebay.de/itm/201324573320

author: MarkL
author_rank: Unknown
timestamp: May 01, 2015, 01:54:45 pm
content: Quote from: Rupunzell on May 01, 2015, 06:45:45 amMy thoughts exactly. The tekwiki link from soren provided a convenient list of all the 7000 mainframes, so I started looking for any bargains.Yesterday I bought a 7633 for US$34 (total - includes shipping). That should do as a stand-in for me to get a project done, and then I can wait until I find an NT-7000. I'm not sure the scope section is functional, and if the power supply is broken it should be easy enough to fix to get the 7A13 running.The 7633 BW on signal out with the 7A13 is limited to 55MHz, but that will be fine for what I need right now.Plus I can salvage the power supply if I still feel like building something standaone. I don't think I could build an equivalent power supply for less than that.The main reason I didn't go for a better (and higher BW) 7000 is that they're just too big. The 7633 is at least on the smaller side. Plus, I don't trust myself to avoid becoming a 7000 collector. Too much of that already and I don't use the one analog scope I have now (2465/CTT).

author: MarkL
author_rank: Unknown
timestamp: May 01, 2015, 02:37:41 pm
content: Quote from: dom0 on May 01, 2015, 07:29:33 amGood to know they still exist. I only looked in the US.I'm not sure either how much the CMRR matters, or at what frequency. I don't know how much Tek relied on the vertical system of the scope to contribute the plugin's overall CMRR. By the time it gets to the back of the plugin it may just be rejecting the power supply and other drift.I can measure some of this when I get the plugin powered up.Or until this all becomes pointless if an NT-7000 happens to show up.

author: dom0
author_rank: Super Contributor
timestamp: May 01, 2015, 03:00:50 pm
content: Honestly I'm not even sure that the NT-7000 was a standard product from Tek.I only found references to it in Germany (that's why I created the page for it at TekWiki), it was manufactured by Tek Germany and the serial numbers on the ones listed on eBay don't match the format of other Tek serial numbers I've seen. The naming scheme also doesn't match up with usual Tek products. Note that NT is a common German abbreviation for Netzteil, power supply. Tek never used non-English abbreviations in their product names, and they don't usually put a "-" between the letters and the numbers.Must be some sort of short lived logo used between the old logo with the tube and the new logo with the serif lettering. I think only a few scopes had that logo, 24xx series probably. So that would put the NT-7000 somewhere like very early 90s.I also couldn't find it in the catalogs. My guess is that they made a (very) limited run of these for some high-profile customers after the 7000-series was discontinued, or something similar.

author: guido
author_rank: Regular Contributor
timestamp: May 01, 2015, 05:18:13 pm
content: I'm wondering if you could have bought a 7704A and split screen and plugin section and then only use the bottom half. Make a cover for the top and done (?). Room for four 7A13s and probably also your output parts.There is also the 7A22 (or even 5A22), which has a similar TM500 counterpart (AM502). If that would fit the bill, you could use a single slot TM501 and it already has an output. It goes up to only 1MHz, but is more sensitive and has filters.Best to have both (i have a 7A13 and 7A22).

author: SeanB
author_rank: Super Contributor
timestamp: May 01, 2015, 05:31:33 pm
content: If you get any 7000 mainframe you can probably split it in half and have the bottom rack on it's own, with the cover cut down to fit the unit, or make a sheet cover for it. The older Tek scopes were adaptable for either rack or free standing use simply by removing the covers, undoing the cabling connecting the halves and then undoing some screws and putting them back in the alternate position so they are either side by side for rack or on top for stand alone. then you have a set of covers that are for the specific style, and which simply screw in.Doing that you can use any dead 7000 mainframe, especially if it is "for parts only" and not in working condition but is reasonably complete. Broken CRT no problem. You might have to find space for the transformer, but this is doable just by losing a slot.

author: MarkL
author_rank: Unknown
timestamp: May 01, 2015, 05:52:02 pm
content: Chopping it up crossed my mind as well. I'll have to see how the 7633 comes apart to do what you're both suggesting. From the manual, it appears all the internal modules are also made to go in the rackmount version, so it may all fit. I might have to use the horizontal slot, but that's ok.It might make a fun weekend Frankenstein project. But I have some real work to complete with it first. So it can live a normal life for now.I already have the AM502 in a TM503. It's a nice amplifier. But I need about 50MHz which is why I started down this path. It's too bad Tek never made the equivalent of the 7A13 for the TM series.

author: dom0
author_rank: Super Contributor
timestamp: May 01, 2015, 06:43:56 pm
content: Quote from: SeanB on May 01, 2015, 05:31:33 pmNope. The 7000 mainframes have different chassis between the benchtop and rack versions. Most of them don't even have two parts (IIRC the 7704A and the 7854 are the only ones).The 5000 series on the other hand is exactly made like you described. You can even remove the display unit completely ; this is actually described by Tek in the manuals. The rear subpanels should also have the necessary stamp outs for the output BNC connectors already.

author: SeanB
author_rank: Super Contributor
timestamp: May 01, 2015, 06:56:55 pm
content: then Tek made some specials, I have some medical equipment that uses a 7000 series top end and a removeable base. This though is the outer shell only, they put in plug in boards that are not the same as the TEK ones, and a backplane that also is not TEK. Nice storage tube though, must one day take it apart further.The other uses a TEK 5 series display unit, and has 2 transformers. Empty bay is looking like it will be a curve tracer one day.

author: MarkL
author_rank: Unknown
timestamp: May 05, 2015, 08:53:04 pm
content: I figured I would update this thread from time to time if anyone else is interested in doing standlone plugins.I got my hands on a 7A13 and powered it up using bench supplies. I'm still waiting for the 7633 to show up.The power requirements are quite minimal. When/if I steal the 7633 power supply it will probably be major overkill, not to mention all the added weight and size.Here's all the voltages that are needed for the 7A13 and the measured current, while actively amplifying a signal:+50V: 75mA-50V: 66mA+15V: 238mA-15V: 204mA+5V (logic): 279mA+5V (lights): 228mAI haven't found any other inputs that are needed for the 7A13.The vertical output can give anywhere between 330mV to 480mV pk-pk differential (Vert+ to Vert-) which should correspond to a full 8 divisions on the screen. That's at least according to setting the sensitivity knob to 10mV/div and feeding it an 80mV pk-pk signal.The output can go further than that, but around 750mV differential there's some visible distortion starting to occur. I'm going to guess that Tek aimed for a nominal 50mV differential per division coming out of the plugins.On the 7A13 the vertical output has a variable range (330mV to 480mV) because the gain of the amp is adjustable via a front screwdriver pot.Each vertical output was terminated in 50ohms as is the case when installed in a scope.