Replacing Leeds & Northrup Binding Posts with Modern 4mm Banana Jacks - Page 1
Forum section: electronics / general

author: garrettm
author_rank: Frequent Contributor
timestamp: December 06, 2020, 01:30:17 am
content: I have a Leeds & Northrup 4385 Shunt Box that I would like to modify to use more friendly 4mm banana plugs. The current binding posts are actually quite rugged and have a nice heavy coat of gold plating. I'm not sure if they used copper or brass for the body, but they look like low thermal connectors. However, they are only meant for use with bare wire and spade lugs--if you can find ones small enough to fit between the retaining ridges (used to keep bare wire from sliding out when tightening).I don't like working with bare wire connections unless I absolutely have to, as the ends oxidize and fatigue too quickly. The Pomona low thermal cables with spade lugs I have are too large to fit without being damaged by the ridges on the sides of the mating surface. That said, I can carefully position them around the ridges on the sides of the binding post, but it’s a hassle to do every time and there is still the risk of damaging these costly cables when not careful. So in an effort to make the shunt more practical and user friendly, I want to at least replace the current terminals with 4mm banana jacks / 5-way binding posts.Since the shunt uses a 4-wire Kelvin connection, calibration of the shunt should not be appreciably be impacted by the modification, as the current terminals are outside of the sense path.I plan to keep the original transparent insulators since the holes stamped into the aluminum are too large to accept any standard 4mm banana jacks that I know of. Interestingly, the diameter of the stock binding post's mating surface (11.4mm) is the same as the hole size used for panel mounting a larger 4mm binding post. So the replacement binding post (with upper plastic insulator attached) will mate flush with the surface of the stock insulators.After some time spent poking around with a pair of calipers, I found the salient dimensions of a replacement binding post to be:Total length >= 56mmend-to-end, plastic and all -- estimate is based on larger style 4mm binding posts I haveShaft length >= 33mmfrom upper plastic base to end of shaftShaft diameter <= 10/32(0.19in / 4.8mm OD, 32 threads/inch)original insulators are fitted with holes to accommodate a 10/32 screw, but a smaller diameter screw could be used without requiring modification.With those parameters in mind, I found two low cost offerings from eBay and Amazon that might work.From eBay: 4 pcs High Quality Hex Head Gold Plated Binding Post Banana Jack Long TerminalLink:https://www.ebay.com/itm/4-pcs-High-Quality-Hex-Head-Gold-Plated-Binding-Post-Banana-Jack-Long-Terminal/392124969526?ssPageName=STRK%3AMEBIDX%3AITQty: 2pairs/4pcs (2pcs red +2pcs black)- Brand New & RoHS Lead Free High Quality, Gold Plated- Total Length:54.5mm- Screw Diameter:5mm- Material:Pure Copper with 24K Gold plated coating- Standard size spreads, accept 4mmm banana plugs- Colors: Red & Black as picture showedI think it's safer to believe these are actually brass with a gold on nickel plating--which should be fine for the current terminals. The 5mm OD will require drilling and the 54.5mm length is likely long enough to not require much bending, if any, of the resistor leads when soldering.From Amazon: CESS Dual Binding Post Terminal - Amplifier/Speaker/Power Cable Connector - Banana Jack Socket - Length 2.3" (2 Pack)Link:https://www.amazon.com/CESS-Dual-Binding-Post-Terminal/dp/B01E6CEUDKScrew Diameter:4.8mm,Total Length:59mmSuitable for 4mm banana plugs.Screw Bolt Diameter 4.8mmColor: Red and BlackThese seem plenty long and the 4.8mm OD are a perfect fit. From reading the reviews, someone had cut the ends and they look to be brass with gold on nickel plating. However, they edited their review to add that the binding posts are "magnetic". So maybe this is some low quality brass with higher iron content or the nickel plating is thick enough to make them modestly magnetic. I can't say for sure, but I doubt it really matters for the current terminals. The voltage terminals on the other hand might need a different part to minimize thermal EMFs.And now my question for the metrology nuts:Is there a better alternative than the proposed parts for a similar or not much more expensive price? I can get either of these parts for around 9 USD for two pairs--which, for unusually long binding posts, seems like a pretty good deal.I suppose I could also just use some copper extensions to lengthen the internal leads so a shorter binding post could work, but I'd like to only have one solder junction per terminal if possible.Anyways, let me know what you guys think. Maybe there is another option I haven't thought of.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 06, 2020, 04:01:49 am
content: Well.... I place a lot of value on originality and those binding posts are really very good. It would be very sad to see them changed.

author: garrettm
author_rank: Frequent Contributor
timestamp: December 06, 2020, 06:56:53 am
content: Quote from: Conrad Hoffman on December 06, 2020, 04:01:49 amI don't disagree.To that end, I always try and do reversible modifications: I don't plan on tossing the old binding posts, I'll simply put them in a box with other original parts that will go back on if I decide to sell it. I have an HP semiconductor test fixture I've reversibly modified to meet my connection needs (BNCs replaced with 4mm banana jacks and the weird HV TNC triax connectors swapped for SHV).Ultimately, practicality must prevail: If the equipment is too hard/annoying to work with, then why use it at all? And if you can non-invasively make it easier to work with--without degrading performance--why wouldn't you?

author: The Soulman
author_rank: Super Contributor
timestamp: December 06, 2020, 11:30:48 am
content: Or make up a dedicated set of leads with suitable spade connectors.For the current force terminalsI* wouldn't be worried about thermal EMF, so get something that works reliably,that doesn't have to be terrible expensive.I use Hirschmann KB2, don't know if it fits the binding posts on your box.*others may.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 06, 2020, 02:55:29 pm
content: Quote from: garrettm on December 06, 2020, 06:56:53 amYes! Reversible good. If there's room, you should put the old parts in a small bag/envelope taped inside the unit.My only other comment is that the quality of eBay and similar parts is suspect. They're probably expensive, but if you can find genunine Pomona or E.F. Johnson that will fit, all the better.

author: garrettm
author_rank: Frequent Contributor
timestamp: December 07, 2020, 10:44:55 am
content: Quote from: The Soulman on December 06, 2020, 11:30:48 amThanks for the suggestion Soulman. I looked at the KB2 and the jaws look like they are also too wide; but the KB2 are deeper than the Pomona parts, so these should fit better around the ridges of the L&N binding posts. The only issue with sideways mounting is I might run into clearance problems with these KB2 connectors since the bodies are pretty long.I suppose I could make custom cables for the shunt but it's honestly easier to replace the binding posts so I can use my existing array of cables.I hate to modify original parts, but as a last resort, I may just file off the ridges on the L&N binding posts and call it a day. Then I can fully seat my Pomona spade lugs and not have to worry about orientation.Conrad, do you know if L&N made a binding post without the retaining ridges? It would be nice to swap in an OEM part to solve my problem.

author: garrettm
author_rank: Frequent Contributor
timestamp: December 07, 2020, 11:06:19 am
content: Quote from: Conrad Hoffman on December 06, 2020, 02:55:29 pmI almost exclusively have Pomona or Mueller Electric parts in my lab from buying random auction lots off of eBay and new parts when I can't find a good deal secondhand. So they were the first place I looked, but all standard small and large sized binding posts from them, HH Smith, Superior Electric and so on are too short--barely reaching above the brass washer on top of the inside insulator. Which is what prompted my excursion into parts of dubious quality/origin. That said, I could always solder on a stout piece of copper wire on the shorter binding posts to bridge the gap. Or crimp some copper tubing on the end... I'll have to think on this. Ironically, filing off the ridges would be quick and cost me nothing but a few minutes of my time. Though I am loath to do it.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 07, 2020, 05:51:13 pm
content: A bit of filing doesn't seem too serious. A bit OT, I don't know how anybody gets through life without having at least a small metal lathe. I'm constantly making up insulators, washers and related connector stuff to take care of fit problems.

author: JohnG
author_rank: Frequent Contributor
timestamp: December 08, 2020, 02:32:21 am
content: Another possibility would be to make up some short copper bars with an open slot on one end to fit in the L&N terminal and mount whatever other connector you want on the other end. The performance hit should be small, and you can always plate them or replace the newer binding post if you don't like it.I feel a little part of the instrument's soul will be filed away if you file the terminals.John

author: guenthert
author_rank: Frequent Contributor
timestamp: December 08, 2020, 03:13:07 am
content: Quote from: Conrad Hoffman on December 07, 2020, 05:51:13 pmUnfortunately most of us have to get through life with a lot less. Said that, I wouldn't even know how to use one. If I ever have something to be lathed, I'll send it your way

author: garrettm
author_rank: Frequent Contributor
timestamp: December 08, 2020, 04:44:48 am
content: Quote from: Conrad Hoffman on December 07, 2020, 05:51:13 pmI've been wanting to get a small lathe for some time, but I don't really have the space for one yet. Would make this whole affair so much simpler, as I would just turn some new insulators to fit the stock mounting holes and use off-the-shelf binding posts without needing extensions.I really like JohnG's idea to make some copper adapters. I would only need maybe two types: one with holes for mating directly with 4mm banana plugs and another with 8-32 or 10-32 threads for mounting a 5-way binding post or piece of all-thread for the larger spade lugs... I don't really have the tools, particularly the thread taps, but I'm always looking for new hobbies. So maybe metal working might be something I jump into next.I would also love to get a gold plating kit to plate all my copper accessories. But maybe sending the parts off to be plated is more practical. Though bare copper should be fine with periodic cleaning.

author: jonpaul
author_rank: Super Contributor
timestamp: December 08, 2020, 11:06:06 am
content: Hello the value of this classic instrument WILL BE DEGRADED if you replace the custom made polystyrene connectors with common binding posts, moist from China.Strongly suggest LEAVE IT AS IS and adapt your test leads:1/ Gold plated spade lugs and test jumpers2/ Place #20 ga solid wire on existing connectors and use clip leads etc.3/ Take good quality test lead wire, attach to connectors and terminate as desired.Just the thoughts of a test equipment aficionado.Jon

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 09, 2020, 09:40:42 am
content: I would be inclined to make some adapters from copper bar and Pomona 3770 low EMF binding posts, with a good clean of the copper and a little DeOxit for good measure before bolting it all together.