The Last Bass Outpost

Oh, and a simple test for this. Select the pickup in question (if there are 2). turn the volume all the way up, plug a guitar cord into the bass, and read the resistance from sleeve to tip on the guitar cord.  If the pickup is good (not opened up) you will read the resistance of the pickup (maybe 8k for single coils, maybe 10k for a humbucker, maybe 20k for a mudbucker, but a resistance in the 10s of k ohms).  if the pickup is open, you will read the resistance of the volume pot (250k for a fender, 500k for a gibson).

Most pickups fail by going open. There are miles of Leetle Tiny Wires in there, and many of them are very old and tired.  Fender single coils usually fail because corrosion on the Alnico poles eats into the wires wound directly on them. Oddly, an open pickup will make some sound (capacitive coupling for you budding engineers out there ) but it will be very tinny and weak.

This is a simple test that doesn't require opening up the bass or unsoldering anything.

This sounds like the one I repaired for you, it was a bad connection to the coil under some 50 year old dead tape.  Very brittle, hard to repair under the microscope (I don't see very well anymore....).  It might have failed again, or it might be the connection on the *other* coil....sorry!

Thanks for the help!  Well, 80uf is a bit much for the 5AR4, so I'm thinking about the recap kit from fliptops that adds a discrete 60 for cap #1, and then 40's in a can cap

http://www.fliptops.net/catalog/p-100023/cap-kit-for-ampeg-b15n-b18n-sb12-v.2-x-seriesamps

XLNT.....will give a try

Thunderbucker here, working on Cataldo's B15, which went down with a shorted PT primary.  Ouch. While schematic searching, I found that it wasn't built according to any schematic I could find. Not even to the schematic pasted on the bottom of the amp. According to the schema on the amp, power supply filtering is done by a  40-40-20-20uf can cap with the first 40uf serving the 6L6s, 1Kohm later the next 40uf serves the screens, then the two 20s serve the preamp and phase splitter, respectively.

What's weird is that  Cataldo's has a 4 X 40uF 500V  can cap (huh, bet that's hard to find these days) and it's been rewired so that the 6L6s are served by 2-40s in parallel.  Since that leaves us one cap short for the various filtering apps, another discrete 20uF cap has been hand-added in to serve as one of the preamp filters.

Check out the pictures.  The first cap cap sections are jumped, then paralleled.  The added cap goes to the pads where one of the can cap sections would have attached, but there is no solder on that pad.  Was this done at the factory?

Odd.  And there is the question that 80uF (40X2) is more capacitance than the 5AR4 is rated for (unless the current draw is low, YMMV etc)

So now I'm hoping some expert will chime in and knowingly opine "Ah yes, that mod went in from October 13 1964 to January 15, 1965, caused by a massive fire at the capacitor factory that caused them to do a running mod....This makes this the most desirable and rare of all the B15NCs...."

Hardcore, shit, that weren't nothing.  While getting ready for our transnational outing, I was putting new pistons and cylinders (from JC Whitney--remember them?) on my bug.  They were "high compression".  I think 7.8:1.  Whew.  Stand Back!  Anyway, while putting them on, I didn't have the band clamp set right and broke one of the top rings.

No sweat, head down to the import parts store and get another set.  Back at the bug, find out that the top ring for my "hi compression" pistons was only 1.5mm thick vs the standards which were 2mm.  Crap.  Went to a couple of machine shops who just shook their heads.

I was not going to miss our convoy out of Gainesville to our Bright Future in Hollywood.  Filled with automotive mayhem--Marty's van ate an alternator in a rainstorm in Biloxi, Carl's Sprite a valve in Tucson, etc.

I had to remove .5mm off that ring.  Armed with a plate of glass off an old TV front (they were flat back then), some silicon carbide dust from my parent's rock tumbler, and an orbital sander, I proceeded to grind away that .5mm, checking for high spots with a micrometer, and pressing harder on those areas, until I had the ring ground down to 1.5mm all the way around.  Carefully put that sucker in and ran that baby all the way out to CA, and still running strong when I sold it several years later.

Actually, I could probably fix this one, if you let me mill off the coil leftovers and buy me a spool of 44.  I don't use that gauge....

Baz, here is your pickup report...
An unusual pickup design—two coils, each serving two strings, like a P bass.  But each coil is on the opposite pole of a central magnet shared by both coils.  And each coil has an secondary magnet mounted to the outside of the coil, which energizes one of the two pole pieces that each coil has.  So, a total of three magnets, four pole pieces, and 2 coils.

The two coils should be wired out of phase to cancel induced mag field noise, and since they are on opposite poles of the magnet, the string signals will still be in phase, like in all humbuckers.

In pix1, we see the central magnet, where the yellow paint is indicating the N pole of the magnet.  The 2 pieces of copper foil are to ground the steel pole pieces, so they will not pick up noise.  The foil wrap touches the steel at the interface between the central magnet and the pole piece . One coil was where all the damage is, and the other is at the other side of the magnet where you see the 2 steel pole pieces.

In pix2 you can see the secondary magnet, its purpose is to magnetically energize the lower of the two pole pieces (it isn't touching the central magnet, so it isn't energized by it—hence the need for another magnet).  Why not a single steel pole piece?  I suspect it is an attempt to reduce eddy current losses in the pole piece, tho I doubt it is necessary, and a single pole piece would make the pickup much easier to build.

In coil1 you can see the 2 pole pieces, the secondary magnet, and the copper coil wires.

Specs:

Central magnet:  Ferrite, .2" X .55" X 2.35"  ~140mT pole strength
Secondary magnet: Ferrite, .2" X .2" X 1.2" (about half as long 'cause it only covers one coil) ~110mT pole strength.
Pole pieces: cold rolled steel,  .062" X .7" X 1.135"
Bobbin: molded plastic, .385" tall, .56" wide, length over all 1.5".  Winding area .3" tall,.285" wide, 1.26" long.  Pole slot 1.13" long X .185" wide.
Coil: wound with AWG 44 solderable.  Intact coil measures  5.50Kohm, L 2.628H, Q 2.641 at 1kHz. (this is with the iron inside, raw coil would be lower L and Q).  I estimate between 4500 and 6500Turns. You'd have to wind one and sneak up on the final value.

Probably a pretty powerful and yet bright pickup.  The overall R would be about 10K (2 coils) and about 5.2H.  Not much losses due to the 2 pole pieces and the ferrite magnets (much less lossy than alnico)
Maybe not very warm sounding, ferrites tend not to sound that way.

Quote from: Baz Cooper on January 19, 2013, 07:59:26 AM
Oh yeah, All good, I know...I should have called...Just was reminded of it. Any possibilities? The tone of these is sick??? Can it be duped???

well, this one is totally dead, if that is what you are asking.  Epoxy potted pickups are not very repairable.  But one coil is intact, so I should be able to get electrical measurements off of it, and the other is broken open so I can tell the wire type and size, take flux measurements on the ferrite magnets.  I should be able to learn quite a lot about it. It is a split coil, like a P bass, but the two coils share a common magnet up the center, then each coil has it's own magnet on the side.  It is an unusual design....

Hi Baz, looks like I dropped the ball on that one, sorry, but you *do* have my email and phone number, you could have given me a kick in the butt to remind me.  I do have the pickup, is this the one?  If so, I'll get to it later this week.  OK to post at this forum?

Quote from: ilan on August 17, 2012, 10:23:53 AM
Oops, I put it yesterday on eBay and it already has one bid! Do you think I can still pull it?

EDIT: I can't end the auction. Still 5 days to go. I'll think of something.

Anyway, a friend who occasionally rewinds vintage pickups took it apart and said it's not just a simple broken solder joint. One coil is OK and the other one is dead. It's a very thin wire, btw, significantly thinner than Fender wire.

I figured that if I can buy a working period-correct pickup for $125, that's a good deal.

No worries, if you end up needing it fixed, let me know. It'll cost just a little more than a spool of wire, about $40-50 (that counts shipping).  I am curious about what is inside these things...

Quote from: ilan on August 07, 2012, 04:41:17 AM
Okay, I'm giving up on the pickup. Bought this 60's Hofner pickup off eBay:

http://www.ebay.com/itm/180935982978?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649#ht_500wt_716



Maybe later I'll try to fix the original pickup.

wow that looks just like the pickups on my japanese Pan bass.  I guess Hofner is where they cloned them from .  I'd be happy to fix that pickup for you, mainly just to see whats inside.  It might just be an internal solder joint.  Charge a nominal fee-not much, tho I might have to buy a reel of wire, if it turns out to be something I don't stock. email at thunderbucker@gmail.com

did you check out the sound clips that carlo posted (link just above the picture of the kit). The bassy part of the kick drum is coming from the CAD mic.  the attack is coming from the condensor near the snare bottom.  For what you say you need, It seems this mic could do it, and like I said, it's not too much money to risk.  Buy it, if you don't like, send it back

Quote from: rahock on May 01, 2012, 11:18:04 AM
That CAD has a low end down to 25hz, that's not bad for that kind of money
Rick

Yeah, if you solo that channel you get a thumm-thumm  and not much more, that mic has a lot of low end and very little hi end, which is actually OK cuz you don't want a lot the other drum noise bleeding in there.  The impact of the kick turns up in the overheads and any mic used for the snare bottoms.

I use this one for recording, it is a large diaphragm cardioid, only $69 at musician's friend, has a lot of low end.  I've been happy with it.  Way more low end than a 57. 


http://www.musiciansfriend.com/pro-audio/cad-kbm412-bass-and-kick-drum-microphone/270774000000000