Cheap triax connector ? - Page 1
Forum section: electronics / testgear

author: michaeliv
author_rank: Frequent Contributor
timestamp: March 02, 2016, 08:14:26 pm
content: Hello,I'm looking for a triax connector for the output of a Keithley 220.The female end ( the one I want to plug into ) looks like this:http://i.ebayimg.com/images/g/OBMAAOSwstxVNT-6/s-l1600.jpgPicture is attached of what I want to purchase.The cheapest I can find on eBay is $40 which seems excessive considering a similar coax connector is under $1.Am I searching for the wrong name or is this expected pricing ?Best!

author: pmcouto
author_rank: Unknown
timestamp: March 02, 2016, 10:16:26 pm
content: You’re doing nothing wrong – Triax connectors are *really* expensive!Sometimes there are good deals on eBay.Keep searching and good luck.Be careful:There are 2 lug and 3 lug triax connectors. Be sure to pick the right one!(linked picture shows a 3 lug connector)

author: michaeliv
author_rank: Frequent Contributor
timestamp: March 02, 2016, 10:32:12 pm
content: Out of curiosity do they use rare/expensive materials, or are they difficult to manufacture, or there is little demand for them ? What's the reason behind the pricing ?

author: Hendry Born
author_rank: Contributor
timestamp: March 02, 2016, 10:37:16 pm
content: Please check :http://www.pomonaelectronics.com/pdf/d_ai_5218_2_03.pdf

author: pmcouto
author_rank: Unknown
timestamp: March 03, 2016, 12:55:59 am
content: Michaeliv,As you can see in the Pomona 5218 assembly instructions, these connectors have a lot of small precision machined parts that are not cheap to make.Also, demand for triax connectors is low and there aren’t many manufacturers producing them (competition is very low).Last but not least, triax connectors are mainly used in professional high-end laboratory instruments and video (broadcast grade) equipment. Compared to equipment price, triax connectors price is insignificant…Additionally, companies using this kind of equipment can easily afford high-priced accessories such as cables and connectors, so there’s no real “pressure” on the manufacturers to lower the prices.Now, you probably have a better idea of the reasons behind the pricing.

author: TiN
author_rank: Super Contributor
timestamp: March 03, 2016, 01:02:55 am
content: If you think triax is expensive, look at SHV version of it (e.g. ones Keithley using for high-voltage SMU and SCS).Also all those bits in triax connector are made from teflon and require extra cleaning, to ensure high insulation resistance. I don't think regular BNC are Teflon-insulated. And metrology-grade BNC's are expensive too.

author: michaeliv
author_rank: Frequent Contributor
timestamp: March 03, 2016, 01:16:32 am
content: Thanks for all the replies. A somewhat unrelated question, why is teflon used either in these connectors or in PCB standoffs. Its resistivity is ridiculously high when compared to air, according tohttps://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity, so most of the leakage would be through air ( for PCB standoffs ). Why not use PET which costs nothing, has a bit lesser resistivity than teflon but still much much higher than air.It seems to me like plugging little cracks in a barrel that is missing it's bottom.

author: smithnerd
author_rank: Regular Contributor
timestamp: March 03, 2016, 02:40:08 am
content: Quote from: michaeliv on March 03, 2016, 01:16:32 amIt has other attractive properties, such as a relatively high melting point and low chemical reactivity. UV stability maybe?

author: vk6zgo
author_rank: Super Contributor
timestamp: March 03, 2016, 03:57:46 am
content: Quote from: smithnerd on March 03, 2016, 02:40:08 amAnother advantage of PTFE is that it can be machined.Probably not a concern with small connectors,but it becomes important in large ones.Yet another is that it does not deform when heated.(within reason-smoke & flames mean all bets are off)

author: pelud
author_rank: Regular Contributor
timestamp: March 03, 2016, 05:44:19 am
content: One easy hack for the 2 lug triax connectors if you don't mind modifying it is to file off one of the lugs. That way you can use 3 lug cables which are much easier to find.Also when searching ebay, they are sometimes listed as "trompeter" connectors, but be careful that they are not twinax which is different.Here is a 3 lug triax cable:eBay auction: #311547280972

author: macboy
author_rank: Super Contributor
timestamp: March 04, 2016, 04:55:20 pm
content: I have a few extra Trompeter (Cinch) brand PL75-55 connectors. I'll part with one for USD $15 or two for $25 shipped. PM if interested.These are technically made for "Twinax" cable which is a shielded twisted pair, but the all important mating surfaces are identical to Triax. They are 3-lug (un-keyed, 120 degrees per lug), as in your pictures. I don't think it would be too difficult to mate these to Triax cable... the most difficult part would be getting a good connection with the inner braid, which would likely require soldering since it is not designed to crimp to it (it will crimp to the outer braid when assembled). You also need to solder the pin. Here is a photo of the exploded connector shamelessly linked from digikey:p.s. Please check if you need 2-lug or 3-lug connectors, as the Keithley 220 came with 2-lug connectors originally. Yours may have been modified by a previous owner, as 2-lug triax is especially rare.

author: michaeliv
author_rank: Frequent Contributor
timestamp: March 04, 2016, 05:32:46 pm
content: Quote from: macboy on March 04, 2016, 04:55:20 pmThanks, but I do indeed need a 2-lug triax connector. I didn't know that there were different types so I just slapped in a photo that I could find.

author: rastro
author_rank: Frequent Contributor
timestamp: March 04, 2016, 07:50:23 pm
content: Keithley and possibly Trompeter make triax to BNC adapters. There are obvious trade-offs going to BNC (2-conductor vs 3-conductor) but it may be acceptable for some applications. The Triax cables are also very expensive.zucca also wrote about converting his 220 to 3-spade triax. Looks like some of the original pictures are missing???https://www.eevblog.com/forum/testgear/keithley-220-output-triax-connector-mod/-rastro

author: woodchips
author_rank: Frequent Contributor
timestamp: March 04, 2016, 08:43:07 pm
content: Where are you? Not really worth posting overseas.

author: michaeliv
author_rank: Frequent Contributor
timestamp: March 04, 2016, 09:07:48 pm
content: Quote from: woodchips on March 04, 2016, 08:43:07 pmI'm in the US, and already checked and there is an ocean in between US and UK, thanks anyways.I don't _*REALLY*_ need it, I'll manage with a hacked in connection, I wouldn't benefit that much from the extra isolation.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: March 05, 2016, 02:23:50 am
content: This is a thread I am very interested in. Would be nice to find some affordable triaxial setups to test with. In particular, I wish there were some affordable triax to bnc adapaters even those seem damn expensive. I have a Keithley 236 that uses these things and it would be nice to utilize the sense lines and what not. I don't anticipate doing measurements taht are sensitive enough to need the guard of the triaxial cable. A BNC should work fine.

author: (*steve*)
author_rank: Regular Contributor
timestamp: June 17, 2017, 04:48:48 am
content: I also have a piece of equipment with a 2 lug triax connector and cables that are 3 lug. This thread had more useful information than the rest of the internet combined, so maybe I can add a little to it. :-)I finally discovered that a Pomona 5299 is a 2 lug to 3 lug adapter and A couple of sellers on ebay have these for reasonable prices. (I got one for less than $US20)There's also a seller with over 200 "Trompeter PL75-24A Triax Triaxial Cable Connector" for $US10 each.It's also worth looking for "Trompeter BJ72" as there are a few bargains to be had at the moment.These are reliable brands (I am not connected to any of the sellers), so might be a cheap option to fix some triax connector woes.

author: alm
author_rank: Super Contributor
timestamp: June 17, 2017, 05:15:05 am
content: Quote from: (*steve*) on June 17, 2017, 04:48:48 amYou sure you got that model right?Pomona 5299is a 3 lug triax (male) to BNC (female) adapter with shield shorted to guard (not good for anything with an active guard like a SMU).There are also adapters from triax to BNC with either triax shield connected to BNC shield with guard open (e.g. Trompeter ADBJ20-E2-PL75) or guard connected to BNC shield with triax guard open (e.g. Trompeter ADBJ20-E1-PL75). The former is safer (shield tied to ground), especially on the high side, but the latter performs better for low currents (keeps guard) and can be fine for the low side where guard is very close to ground, low voltage work or setups where the connector and cable shields are protected from touching.All of this is three lug. Two lug triax is legacy and my suggestion is to either change the connector to two lug (there is an old thread about changing a Keithley 220 output connector from two lug to three lug on this forum), or get a 3-lug to 2-lug adapter (e.g. Keithley 6172), or make one from a 2-lug male, short length of triaxial cable, and 3-lug female.Quote from: (*steve*) on June 17, 2017, 04:48:48 amMake sure (as is the case for these two) that whatever you are buying is for TRB connectors. There are also thread, larger and smaller versions that are not compatible.This documentshows some of the variants.

author: pmcouto
author_rank: Unknown
timestamp: June 17, 2017, 09:33:21 am
content: Keithley 6172 is a 2 slot male to 3 lug female Triax adapter.But it’s not cheap…http://pt.farnell.com/keithley/6172/triax-adapter-2slot-male-3lug/dp/2672724Regards,Pedro Couto

author: alm
author_rank: Super Contributor
timestamp: June 17, 2017, 10:07:16 am
content: Few things related to triax are cheap. Depending on how you acquire them, a 2-slot male connector, piece of triaxial cable and 3-slot female connector may not be that much cheaper. I believe Pomona and Trompeter may make similar adapters, but I do not have the part numbers handy and I am not sure if they are still current products. Is there any equipment currently in production that uses 2-slot triaxial connectors?Also you may not have to pay list prices. Things might be available on eBay, or even through regular distributors that have surplus stock. I paid much less for mine brand new fromTop Elektronika number of years ago.

author: (*steve*)
author_rank: Regular Contributor
timestamp: June 18, 2017, 03:14:58 am
content: Quote from: alm on June 17, 2017, 05:15:05 amI'm well aware of the triax to BNC converters and I blame <insert favouite blame thing here> for totally failing to spot this, even though I looked up the spec sheet.Oh well, I can use it for my Keithley 600B. I already have a converter to BNC but my regular coax to alligator clip cable has a resistance of 50G\$\Omega\$. I can probably use this to allow me to connect my nice Keithley triax cablesAnd I guess I'll be filing off that damn lug after all.Thanks everyone for the heads-up.

author: ebclr
author_rank: Super Contributor
timestamp: November 08, 2017, 05:31:35 am
content: https://item.taobao.com/item.htm?spm=a1z10.3-c.w4002-2384871945.56.29ed68dexQhfcl&id=536567327738

author: TerraHertz
author_rank: Super Contributor
timestamp: July 15, 2020, 02:25:50 pm
content: I've been looking for affordable triaxial BNC connectors (and cable) for a while. I have a HP 4140B pico-amp meter I need to connect to a test fixture, and it's required to use triaxial 3-lug BNCs and cable.The triaxial cable is Belden 9222. Low leakage, low microphony.Suitable connectors are Pomona model number: 5218. See:https://www.pomonaelectronics.com/products/connectors/bnc-triaxial-m-3-lug-belden-9222-triaxial-cableBNC Triaxial (M), 3 Lug For Belden 9222 Triaxial CableBut these cost around AU $78 each, and the first price break is at Qty 25. Still not much cheaper. Too rich for me.Anyway, I finally found an affordable source on Aliexpress.Store name: Chengtec StoreTriaxial BNC male connector, domestic high quality, JY75-1.5 / JY75-2 / JY75-3 1553B cableCurently AU$ $23.98 each (15.19 USD), 10% off for 5 or more.I'd originally ordered just two. They arrived recently and are well made and fit Belden 9222 cable perfectly.The construction allows for re-using them if you need to replace the cable. A big relief to me, since they are still quite expensive.Insulating material seems to be PTFE, so hopefully they are suitable for the pA meter.It appears the store only recently listed these connectors, and I was their first buyer. Perhaps they'll lower the price if they start getting significant sales numbers?Here are some pics I took of one I received.Incidentally I also found an ebay seller (wzjworld) with some used Belden 9222 for sale. That cable is OK too, and cheap.

author: noreply
author_rank: Frequent Contributor
timestamp: July 15, 2020, 09:23:10 pm
content: Just be carefulwith 'ebay' or Amazon -as you usually get what you pay for.I got some 50 ohm BNC inline terminators from Amazon - these were VERY reasonably priced - but compared to an original Rigol part - which is 5 times more expensive - their quality was reflective of the cost.I know the Triax connector is not same as what I am referring to - but the concept of an alternative 'cheaper' item stays same.The Rigol BNC is a machined part - expensive to make - the 'Amazon' BNC is cast metal -poor tolerances - much cheaper to make - not to mention theRigol termination resistance is spot-on 50.0 ohms, the 'Amazon' part is 49.8 ohms.Remember you tent to get what you pay for.Good luck in your selection

author: TerraHertz
author_rank: Super Contributor
timestamp: July 16, 2020, 01:30:31 am
content: All good points, and thus why out of caution I initially only bought two of these 'cheap' triax connectors. Also why I posted photos of them here, to show that they are not the cheap diecast zinc alloy rubbish that does exist. These are machined brass, nicely plated, seem to be close-tolerance parts.Whether the 'gold' plating is actually gold, and what's the plating thickness, don't know.As for impedance matching, for the frequencies involved in the target system (all under 15MHz) that isn't going to be a significant issue. Down in the pico-amp measurements range a far more significant factor will be surface and bulk conductance of the insulating materials. But if those are half-way decent (teflon/PTFE) a fingerprint on the insulator surface would swamp the material characteristics anyway.

author: graybeard
author_rank: Frequent Contributor
timestamp: November 21, 2022, 07:07:46 pm
content: I would be wary of Pomona Electronics triax connectors. Where I work we use hundreds of triax connectors per year for production test. For many years we used Pomona Electronics without a single failure. Since Pamona shifted their production to China we have had many failures of their triax connectors. We now use Trompeter triax connectors exclusively. Trompeter's triax connectors have been trouble free.