60's Mini HB repair advice sought!

[jimboyogi]

Hi all,

A friend of mine bought a '67 Epiphone Riviera, that did not work quite right. He investigated, and found that the neck pickup was very damaged, and not working at all. When he opened the pickup, it appears that one of the bobbins had numerous broken wires, and that it quite probably came from Kalamazoo that way

Here's a link to an interesting forum thread detailing his investigations -
OffsetGuitars.com ? View topic - Well ... it's Kalamazoo conspiracy theory time...


He's asked me to have a go at repairing it, if possible. I wanted to check with the extensive brains trust here, and ask a few questions before I get started on it. I want to save as much of the original wiring as possible!

1 - are 60's Mini HB (MHB) coils potted, and if so, what with? If it is potted, should I try to soften the potting compound before I start unwinding?

2 - I have read some internet wisdom that proposes that these pups were wound with ~42.5 AWG, to explain why they have a different sound to later versions of MHB, which are reportedly wound with 42 AWG. Does anyone here know if this is true?

3 - My plan is carefully unwind, counting TPL and winds, as well as watching the wind pattern. To keep unwinding until I get through all of the breaks, and have good electrical continuity. Then to join new wire to the old, and rewind as closely as possible to the removed wire.
How does this plan sound?

4 - I have only single build poly wire in stock. Is there a legitimate sonic reason for buying some PE wire for this job instead?

[big_teee]

You must have the patience of Job to reuse wire?
I would cut it off and rewind it with 42 or 43.
Like pointed out on other threads here, 42 is about the size 42.5 was in the past.
Most 42 used to measure around .0028" or bigger, now most is around .0026"-.00265".
GL,
T

[mr fab]

if the old pickups were potted they were potted in wax. however I had a 70's les paul deluxe with minis and as far as I could tell, they were unpotted.

if they are wax potted, you will have a hard time unwinding it without breaking the wire. softening the wax may help. hopefully the break will be close to the outer layers and not at the start.

working out the TPL by hand winding is probably a good thing, however very time consuming.


I would use poly wire, I believe Gibson moved over to poly wire in the 60's.

just as a note, I always found old Gibson mini's quite prone to feedback and squeal. some double sided tape between the top of the bobbins and the inside face of the cover will help enormously

let us know what you discover... pictures of the innards of the pickup would also be cool.

[jack briggs]

I've rewound a few 60s and 70s minis - from Gibsons and Epis and from Silvertones (Gibson made them for Silvertone, as well). I don't think they were originally potted, but from my experience you want to keep it that way if you want any kind of clarity from the neck pup. SK Guitar Specialties site shows the minis were wound with 42PE; 4250 turns per coil. I like an offset on the neck to help with clarity. Of course they switched to poly coated wire on clear bobbins sometime in the 70s (I think).

If you choose not to pot just lay a piece of masking tape between the magnet and bobbins to cut down on microphonics, as well as a piece on top of the bobbins before soldering the cover back on.

Best of luck!


cheers,

[Jim Darr]

I've seen a lot of these minis and none have ever been potted from the 60s or 70s. Gibson switched to poly wire in around 1963. Go with 4250 turns of 42 AWG. I'd just use the wire you have.

You can always mic the wire from the bad coil to get the OD measurement and match it as best you can to some new wire (thickness will very from batch to batch and manufacturer to manufacturer, coating build thickness will also effect total OD). Try to match TPL if you can control it on your winder.

The mini bobbins usually have a black mark on one side to denote top from bottom...so be sure to wind in the correct direction while correctly orienting the top and bottom...if you wind in the wrong direction or mis-orient the top/bottom the pickup will sound very week but still give you the proper Ohms reading.

Good luck. Post some pics for us.

[jimboyogi]

Great advice, thanks everyone!

Of course I'm hoping that the breaks are in the last few winds If they are near the start, then I can't guarantee my patience will hold out. I don't have the pickup yet, but will update when I get started.

Re. the linked thread, investigating the factory dud pickup. Has anyone ever come across other Epi/Gibson pickups that were obviously non functional from the factory?

[Jim Darr]

Re. the linked thread, investigating the factory dud pickup. Has anyone ever come across other Epi/Gibson pickups that were obviously non functional from the factory?

Not me, I haven't.

[Jim Darr]

Jimboyogi,

I took some time to look at the link in the original post. While I agree that there is definitely a problem with the neck pickup, I believe the damage to the pickup came after it left the factory.

Let me explain.

These mini humbuckers are much more delicate than the larger bigger brother HBs for any modding. My real first experience with one came on a mid-60’s Epi Crestwood Custom. I was already into modding and upgrading guitars and thought I was pretty good at it by this time…NOT!!!

My idea was to remove the cover to get more highs…just like I had done several times with full size HBs. Much to my surprise the internal guts of the mini, while similar to their full size brother, were much different in one key aspect…the bobbins were not fixed to the base plate. As soon as I removed the cover, both bobbins fell off breaking the hookup wires. I then tried to take the tape off to see where the wires were broken, but caused more damage in the process. I was lucky as I broke the wires on the end of the wind and was able to remove a few wraps then reconnect the hookup wires. I learned an important lesson…never take apart a mini unless it is already dead.

Back to your link…In looking at the pictures it appears that the cover may have been removed from the neck pickup at some time. If this is indeed the case, then I suspect that somebody caused the damage to the pickup after it left the factory perhaps as I did to my Crestwood. My results were similar to the pics in the link.

I can’t imagine why the factory would allow a bad pickup to go out especially during the mid-60s, even if the guitar was marked as a factory second. Most of the 2nds I’ve seen from this era were finish blems if I could even figure out why. I would think that QC would have done a simple Ohms test to check for proper DC resistance prior to assembly and would have caught the problem with the pickup before putting it in the guitar. Pickups were pretty cheap back then even at retail (I was paying 30-35 bucks for a full size Gibson pickup at my local, small, Gibson dealer back then --- so wholesale had to be around $15-20 and true internal cost much lower).

So, and without seeing the actual pickup in question, I came to a different conclusion. My best guess is that somebody like myself, caused the damage after it left the factory. Even if the cover was removed at some point, a good hot soldering iron could always reflow the solder joint so it would look as if it were untouched 30 years after the fact.

Any way that is my 2 cents. Let us know what you think when you get the pickup in-hand.

[jimboyogi]

Thanks for your in-depth answer, thoughts, and experience Jim.

I honestly don't know how I would be able to tell when the pickup was damaged, particularly because it has already been opened/re-opened. Hopefully, if it is a similar situation to your experience, the breaks are all near the end!