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'76/'79 Thunderbird pickups and wiring

'76/'79 Thunderbird pickups and wiring
« on: January 04, 2008, 05:20:11 AM »
Hi,
I've been checking out this site for about a year, but never posted anything before...
There are a few oddities about '76 and '79 T-Birds that I wanted to address.
First of all, every Thunderbird in this series that I've owned (I've owned eight of the beasts since 1980 as well as five '64 reverse IVs, one non reverse IVs, two non reverse IIs, (one of the non reverse 'Birds was factory natural mahogany,looked like the back of a Les Paul gold top) and two Epi Embassies) has had the pickups wired in SERIES instead of parallel as the '60s T-Birds were.
This makes for an incredibly muddy, blaring tone with both pickups on that I find useless. Why Gibson did this I'll never understand.
I suppose it's sacrilege these days, but since I'm skilled with a soldering pencil I rewired the '76 and '79 I currently own in parallel and they sound fantastic!
These basses date to the era when Gibson was using 100K and 300K pots. I took the original pots apart, swapped the tracks for 500K CTS tracks and reassembled them. Also made a big difference.
The other anomaly concerns '79 T Birds only...both of the two '79s I've owned had pickups that read really LOW, in the 3-5 K range Both basses had very loud, normal output. I've also had '70s EBs with mudbuckers that read stupidly low like this, yet had full output. I seem to recall reading a post on here regarding this topic a while back. Someone said that Gibson probably used a heavier gauge magnet wire, this would yield a low impedance but high inductance, hence strong output.
So...if anyone out there thinks they have defective pickups in their '70s Gibson, you probably don't.
Gibson was likely experimenting with this idea to gain some of the advantages of low impedance pickups without the inconvenience of active electronics. In those less sophisticated days, very few (if any) players were measuring their pickups' DC resistance, so there would have been no need to explain or even mention this in any of their literature.

Happy new year,

Bill

doom

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'76/'79 Thunderbird pickups and wiring
« Reply #1 on: January 04, 2008, 11:40:56 PM »
Yes that is interesting. I have two '76 Thunderbirds and one of them is refinned. When I got it I noticed that when I dialed both volumes up full the bridge pup seemed to overvoice and cancelling out the neck pup making the bass sound very thin. I noticed it had been wired in parallell. Once I rewired in series it sounded like my original Sunburst (in fact better). I thought it was due to the bridge pickup measuring a higher resistance I figured it had higher output thus cancelling out the neck pup. Interesting to see you managed to get a good sound wiring in parallell.

'76/'79 Thunderbird pickups and wiring
« Reply #2 on: January 05, 2008, 12:01:41 AM »
It's the other way around...parallel is the more usual way a 2 pickup bass would be wired, i.e., as an example, a bass with two 8K ohm pickups would read 4K with both pickups full on in parallel. In series they'd be 16K ohms, twice the resistance of each pickup, very hot and midrangey.
These '76 and '79 T-Birds came from the factory wired in series, which is unusual. It's really too much for two humbuckers, way over the top. Parallel wiring will be brighter, cleaner, and a more even response.
The neck pickups on these basses read lower that the bridge pickups...my '76 has a 6 K neck pickup and a 10K bridge pickup. It's a similar ratio on my '79, although the overall numbers are lower.
The neck pickups on these usually have a 3 conductor wire and the bridge oickups have a regular Gibson braided lead. With the stock (series) wiring one of the neck pickup's 3 wires goes to one of its volume control's lugs and the other wire goes to a different lug on the same pot.
Naturally, the shield goes to ground.
It's a pretty strange arrangement.
I have a pic of the stock Bicentennial Bird control cavity, not sure how to post it yet, though

doom

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'76/'79 Thunderbird pickups and wiring
« Reply #3 on: January 05, 2008, 12:29:16 AM »
Since I knew they are supposed to be wired in series I thought the cancelling out came from the pickups being matched for this wiring. I've even seen those who had ca 6.5k neck and 14k bridge pups compared to the new 'birds which I believe is about 9k each.

'76/'79 Thunderbird pickups and wiring
« Reply #4 on: January 05, 2008, 12:36:31 AM »
Oh, OK, I see...
I think it's the discrepancy between the bridge and neck pickups that are responsible for your problem. Oddly, my '76 with the 6K neck PU and 10K bridge in parallel sounds quite balanced. 4K is a lot of difference, too. Usually the bridge pickup beig 1K hotter makes for a good balanced pair.
'60s T-Bird pickups are aroud 10K, by the way. They are very different in construction and sound from either the '76 3 screw TB pickups or the T bird + units.

doom

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'76/'79 Thunderbird pickups and wiring
« Reply #5 on: January 05, 2008, 12:40:21 AM »
Maybe the height adjustment made a difference in my case as well. I don't remember how the pickups were set up at that time.

jules

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Parallel and series
« Reply #6 on: January 05, 2008, 09:35:40 PM »
Hi Bill, and welcome!

sounds like you've had some great basses. Do you have any pics you can post to illustrate the wiring differences? I would like to check my '79...

Does anyone know.... how tricky would it be to create a mod that allows you to change from parallel to series? Would be nice to hear the diference instantly without changing any other variable

'76/'79 Thunderbird pickups and wiring
« Reply #7 on: January 05, 2008, 09:49:42 PM »
Thanks...yeah, I've had a few nice basses. Had a beautiful '65 EB-3 about 10 years ago that I had no intention of selling, but you know how that goes. (Have a '67 now with the skinny neck and narrow knob spacing but still with the handrest...paid way too much for it, but you how that goes as well, no doubt!)
Interesting story about '76 'Birds...they were available until mid 1981 at a local store, I think they were ordering them from a distributor that still had them in stock. So even at a time when the '79s were discontinued, I was buying MOS '76s in sunburst or black for $500.00! I bought 3 this way...don't have any of them anymore, though.

Back to the T Bird parallel/series thing, I guess a switch coud be installed to do that, but it would have to be a pull pot to avoid drilling a hole in the bass. I think it's need to be a double or possibly triple pole switch to accomplish this. Personally, I'd never use the series mode anyway, as I mentioned before, I found it to be pretty useless.
The pic I have of the stock T bird wiring isn't from mine, I lifted it from ebay. I can take a pic of the parallel wiring as I have it now, no problem.
Bill

Stock '76 Thunderbird wiring (pickups in series)


Modified '76 Thunderbird wiring (pickups in parallel)

jules

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series and parallel
« Reply #8 on: January 08, 2008, 04:20:21 AM »
My '79 is in series too. I've examined just two 1990s thunderbird control cavities, and both had the parallel wiring.

I wonder what was so special about the 70s ones.

Anyone looked at an Epiphone or an Orville?

'76/'79 Thunderbird pickups and wiring
« Reply #9 on: January 08, 2008, 02:42:50 PM »
I think the series wiring was something Gibson was experimenting with in the '70s. Rippers have series/parallel switching, for example.
The '70s T Bird pickups are odd beasts as far as design goes too, I've head them referred to as a "sidewinder' humbucker, never took the covers off one, so I'm not sure exactly what that means. The design of the pickups might be why Gibson wired them in series, although, as I've said, to my ears they're way too hot in series. By the way, do the pickups read low DC resistance in your '79 Bird?

I would bet that the Epis are wired in parallel. Never played an Orville or even seen one in person.

doom

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'76/'79 Thunderbird pickups and wiring
« Reply #10 on: January 08, 2008, 03:40:21 PM »
The '76 pickups are Sidewinders which means they have both coils lying down pointing in a forward and backward direction instead of both pointing up. Instead of the Mudbucker Sidewinder using pole screws the '76 pickups have a blade magnet pointing up and it is made like a T so the coils surround each "wing" of the T. The Ripper pickups are also Sidewinders BTW.

'76/'79 Thunderbird pickups and wiring
« Reply #11 on: January 08, 2008, 04:12:28 PM »
OK, thanks for setting that straight.

'70s T-Bird pickups are definitely brighter than '60s ones. The '80s-present "Teflon T-Bird" pickups, as Martin Turner calls them, are pretty bright sounding too.
I have taken the covers off '60s T-Bird pickups. They are a straight humbucker design...the bobbins were molded for a Gibson steel guitar, I think, with pole piece holes that were filed out at the factory to fit a magnet in lieu of pole pieces. This is basically pretty similar to the Firebird guitar pickups, and usually makes for a fairly bright sounding pickup, and they are not at all what you'd call muddy, but not nearly as trebly as later TB pickups.

Interestingly, pickups from reverse T-Birds with nickel plated covers seem to have cream bobbins, same  as '59 Gibson PAF humbuckers with cream coils..The chrome cover pickups in non reverse 'Birds have black bobbins.  (The '65 non reverse T Bird I used to own had nickel parts, but I don't remember if I ever checked to see if it had cream or black bobbins).

I once read (I think in Guitar Player magazine at the time it was current) that the Ripper pickups and electronics were designed by Bill Lawrence and that they were an air coil design. That would mean that one coil had no metal core and functioned as a dummy coil for hum cancelling only for (theoretically) single coil-like tone. It could still be a sidewinder with an air coil, or course.

Bill Lawrenece also designed the electronics for the Framus Nashville Bass, which is a little biit Ripper-ish, if i remember.

'76/'79 Thunderbird pickups and wiring
« Reply #12 on: January 09, 2008, 12:39:02 PM »
My Bicentennial is wired in series too (if that is what that first pic shows), not that I really pretend to understand what that means (does it mean that the tone signal first goes into one pup and then from there into the other pup before hitting the jack?), but my aural observations are somehow different:

1. On both my sixties birds and my nineties and post millenium Birds, I find the sound suffers if I have both pups on full throttle. My preferred sound is to have the neck pup full throttle and the bridge pup dialed down to just that "sweet spot" where the neck pup opens up yet the bridge pup can still be heard for added attack. Dialing up the bridge pup too high takes away authority, volume and a natural sounding representation of all frequencies from the overall tone signal IMHE (... = in my humble ears).

2. I don't have that effect with my Bicentennial - it is the only TB I own where the signal gains authority if poth pups are dialed up in full, there is no loss of volume then, but actually a gain. Yes, the sound gains mids then, but I like that, because compared to both my sixties and modern Birds, my Bicentennial is noticeably less loud. I never attributed the "both pups full blast sound best" effect of the Bicentennial to wiring in series or in parallel because I don't think in those terms. I thought that the Bicentennial bridge pup just has a lot less ohms than the neck pup and that hence there is less cancelling out between the two. Now I've learned from this thread that it is the other way around, that the neck one is the weak pup, but I guess the fact that they have sizeably different ohm measurements still has something to do with the sound.

3. I agree: The Bicentennial pups have the most presence in sound, it reminds me a bit of the LP Sig in fact. My (formerly owned by George Carlston) Jap ed only single pup mid-eighties TBird has that glistening (but vintagy sweet) presence as well as it features a single Bicentennial pup. On some fancy meter the modern TB Plus pups might show even more presence, but I don't hear it because the bass and mid range output of these pups is so raucous it drowns out much of whatever presence there might be. The new generation TB Plus pups ("new design" as Gibson calls them) on my 2007 ltd ed Stealthbird and GoW Zebrabird have even less presence than my 1997 TBird has.

4. But to add to the confusion: I have a 1980 Gibson custom built all Korina short scale Explorer bass that features what are obviously Bicentennial pups, albeit in gold. By the looks of the control cavity that bass is wired in series yet it "acts parallel", i.e. dialing down the bridge pup increases volume and authority of the neck pup. Maybe the ohm difference of the two pups used there isn't quite as large as on the Bicentennial?

Uwe

'76/'79 Thunderbird pickups and wiring
« Reply #13 on: January 09, 2008, 01:52:57 PM »
When 2 pickups are wired in series, it doubles the output, in parrallel it cuts it in half, that's why you notice a loss of output with both pickups in parallel and a louder output in series. I never found the loss of output in parallel to be too extreme. Two pickups in parallel full on is and has always has been my basic bass sound, by the way. Different strokes for different folks, I suppose.
Two humbuckers in series yields a blaring, mondo distorto lower midrange-y sound that. for me, is useless, since I like the clear, piano like quality of the old T-Birds.
In a stage situation, 2 T-Bird pickups in series are a mess...they don't cut through the mix. Depends on what sound you want, though. If dirt is what you're looking for, though, series might be the ticket.

Beautiful Explorer bass! That was a one off, I guess? Never seen another one.
Why it would be wired in series yet have lower output is a mystery to me.

It seems that all '76-'79 T-Birds have lower ohm neck pickups, why, I don't know. On mine, the volume difference isn't that drastic.
The neck pickups on those basses have a 3 conductor wire while the bridge pickups have the usual braided lead.
If any NOS '70s T-Bird bridge pickups ever turn up on eBay, I'd still probably but a couple and use them for neck pickups in my 'Birds so there would be 2 matched pickups...

'76/'79 Thunderbird pickups and wiring
« Reply #14 on: January 09, 2008, 01:59:55 PM »
I just noticed a interesting thing about your Explorer bass...it's an '80, yet it has a '60s style bar bridge. The tuner configuration is kind of hard to see in the photo, but it appears to be 3 on one side, one on the other?

 

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