Replacing jack on my old MOTS Supro

Greg Moynihan · Post by **Greg Moynihan** » 4 Nov 2014 8:55 am

Hi, I have a '50s MOTS Supro with several cosmetic flaws, but it could make a decent player. I recently had the PU re-wound professionally.

I've decided I want to replace the microphone style connector with the standard 1/4 jack. However, this is complicated because that old jack screws into a robust metal tube that is glued quite solidly into the body. This tube is straight, threaded on the inside, and a few inches long. It passes from the outside surface into the body cavity by a couple of inches.

The diameter of the tube is roughly the same as the switchcraft barrel jack that I want to drop in there, so, it must come out. The hole in the MOTS wrap will have to be enlarged a little bit, and I'll probably need to drill out the glue and wood that surrounds this metal tube.

Still, I want to proceed with the mod, if possible. Does anyone have experience with this work? Any tips or pointers are much appreciated.

Best regards,

Greg Moynihan

Tom Pettingill · Post by **Tom Pettingill** » 4 Nov 2014 10:48 am

Some heat should help soften / loosen the glue. If you could get a steel bolt, pipe nipple, something that bites the inner threads, you could heat the nipple with a torch and it should slide out if its only glue holding it in.

Joe Snow · Post by **Joe Snow** » 4 Nov 2014 2:27 pm

I recently did that with my Supro. After looking in vain for guidance, I stubbornly proceeded. There is a nail going through the tube. I worked it up with skinny needle-nosed pliers until the head showed through the mots (otherwise not apparent), then pulled it out with pliers. I pushed on the back of the tube until I got it out a bit and brutally pulled it out with pliers and my knees against the body of the steel. It was tough, but eventually worked its way out. The tube jack (an endpin jack) went in fine, but there is no room at the back to put the nut on. I may go back in and do some "micro-carving" to accommodate the nut. Meanwhile, I forced a cedar wedge between the jack and the body, and have played on stage several times since then with no movement of the new jack. Incidentally, I joined new wires and old with solder and small wire nuts so there's plenty of wire to redo things if necessary. Hope this makes sense.

Erv Niehaus · Post by **Erv Niehaus** » 4 Nov 2014 2:34 pm

If you don't want to go through all that trouble, there is an adaper that you can get so you can use a regular 1/4" cord end.

Joe Snow · Post by **Joe Snow** » 4 Nov 2014 3:02 pm

The adapter works fine, unless you are gigging with it often. At the guitar side of things, my connection failed several times. Unscrewing the adapter tended to want to take the connector with it, making the tip connection fail. 1/4 inch jack is much more solid. Some people drill a 7/8 hole to use a tele style jack, but I didn't want to do that. The end-pin style jack fits the hole without modification of the body.

Joe Snow · Post by **Joe Snow** » 4 Nov 2014 3:38 pm

By the way, I didn't realize there was a nail going through the barrel until looking with a flashlight. This is a 51 double neck Supro 6 string. The head of the nail was under the mots.

Tom Pettingill · Post by **Tom Pettingill** » 4 Nov 2014 4:02 pm

Great info Joe!

Joe Snow · Post by **Joe Snow** » 4 Nov 2014 4:19 pm

I looked among my bolts and parts trying to find something to match the inside threads of the barrel to no avail. Finding that would be an advantage to pull the barrel out. The glue broke free with no problem. The barrel is just really tight. And the nail is a critical part of holding it in.

Greg Moynihan · Post by **Greg Moynihan** » 5 Nov 2014 8:11 am

All very helpful tips, thanks so much! A quick peek inside that hole with a flashlight shows me that cruddy old nail right through the middle of the tube. I can even see its head peeking through a small hole in the wrap, which is all hidden under the top plate.

I though carefully about keeping the instrument stock, that is my usual MO. But, I have much trouble and bad luck keeping track of special parts and cables. If it were a quality, collectible instrument, I wouldn't dream of modifying it. However, this instrument is a cheapie and it's for the sake of fun, convenience, and experimentation.

Edwin Allen · Post by **Edwin Allen** » 5 Nov 2014 9:47 am

I used a switchcraft 151 thick panel phone jack to replace the Mic connector on my Supro. It works great.

Greg Moynihan · Post by **Greg Moynihan** » 11 Jan 2015 2:40 pm

Well, I will say this, I now fully understand how nailing the jack tube in the guitar body is an effective and cheap manufacturing method. The nail head on mine was buried a little, so I had to chisel a bit around it to pull it out. Next, I plan to either chisel or rout the cavity a little bit more to make room for the output jack's nut. All is concealed under the control plate anyway.

Greg Moynihan · Post by **Greg Moynihan** » 11 Jan 2015 4:40 pm

Alright, back from the garage, here's what I did:

I made a quick hardboard template for the cavity enlargement, and clamped it all up:

I made one error, which was starting with 1/4 inch bit that wasn't deep enough. I switched to a nice long 1/2 inch bit to finish, which left me with an awkward step in the side of the cavity. But, it's all hidden work. This is my first time routing on a real guitar, and I am glad that's over with!

Greg Moynihan · Post by **Greg Moynihan** » 11 Jan 2015 7:59 pm

Everything is back together, and sounds quite dandy! Thanks fellas for all the help on this one, extracting that old jack was a bit tricky. The re-wound pickup sounds pretty hot, thanks to Tom Brantley at rewindpickup.com.

Now I have a viable instrument for test-driving a few more tunings...