Lawrence 705 Resistance Readings/Lengthening Short Leads

Jim Cooley · From: The 'Ville, Texas, USA

I have 2 original (chrome surround) Lawrence pickups. They were both sold to me as 705s. When tested with my multimeter I get the following readings:

Pickup #1 has one insulated lead surrounded by braided ground. Both are inside the same casing. It reads 16.4 Ohms. I believe that makes it a 605 instead of a 705. The reading is consistent. Is there any reason to believe it's not a 605?

Pickup #2 has 5 leads. The green and white are twisted together. The black and bare wires are twisted together. The remaining wire is red. Checking across the green/white and black/bare gives a reading of 10.4 ohms. Separating the black and bare wires yields the same reading. There is no reading if I use the red wire in any combination. Should the 10.4 reading be doubled to equal 20.8? That's right on a 705's resistance. Is there something wrong with the pickup? Anything else to check?

Both pickups have short leads. If I use either one, can I solder individual wires to each lead and use shrink tubing around all of them? Do I need to use shielded wire? If I need shielded wire, is the a certain type and gauge? Where can I buy the shielded wire?

Stephen Cowell · From: Round Rock, Texas, USA

If there is no reading using the red wire then you have an open coil, or other open connection. Trace the red wire carefully and look for a broken winding etc. You should have another 10.4 *k* ohms from red to g/w, and 20k across red to black.

I believe you're right about the first pickup, but I'll let others confirm.

For a short run you don't really have to use shielded wire. Solder them well and insulate the connections with heat shrink or tape.
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Lane Gray · From: Topeka, KS

If pickup 1 only has two wires, I'd say it's counterfeit. Bill made them with the full set of wires.
I agree, pickup 2 is broken. Rewind time.
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Jack Stoner · From: Kansas City, MO

In several "lengthy" discussions with Bill Lawrence, he emphasized that the DC resistance is not a valid reading and he didn't use it for his pickups. Thus two of the same model pickup can have difference DC resistance but all the applicable AC parameters will be the same and the pickups will sound the same.

We get hung up on the DC resistance of a pickup as THE measure of the pickup. The only time the DC resistance is valid is if everything is exactly the same - same coil wire, exact same magnets, etc. Thus, for example, an Emmons pickup wound at 17K and a Wallace True Tone at 17K are not the same.
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Jim Cooley · From: The 'Ville, Texas, USA

Stephen - I was afraid that was the case. If I can figure out how to get inside the pickup, I'll try to trace the red wire. I can unscrew the base plate. It appears to also be stuck on with adhesive. Should I be able to remove the surround?

Lane - I didn't think about pickup #1 possibly being counterfeit; didn't know there were counterfeits out there. I had a narrow mount chrome surround 705 with only two leads in my LDG for a while. It worked great. No coil tap of course, but other than that, it was fine. FWIW it reads 20.5 Ohms. I still have it. It also has short leads that are spiced inside if some shrink wrap tubing. Hmm...

Jack - I am aware of that. I've read at least one paper that Bill Lawrence wrote on the subject. It's very interesting and makes a lot of sense. I just thought that since there is such a disparity in readings it might indicate a problem, especially since the reading is almost exactly half that of many 705s.

Does anybody know who rewinds these?

Lane Gray · From: Topeka, KS

I'd ask the two usual suspects, Wallace and Lollar.
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Stephen Cowell · From: Round Rock, Texas, USA

Bruce Derr · From: Lee, New Hampshire, USA

Lane Gray · From: Topeka, KS

I didn't know that, Bruce. I'd feel cheated if I got a two wire 705
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Bruce Derr · From: Lee, New Hampshire, USA

Lane, me too!

Sounds like Jim's 2-wire narrow mount 705 has the other two wires tied together under shrink wrap but possibly still accessible/extendable.

Jim Bates · From: Alvin, Texas, USA

Sorry to correct the thread, but I bought my 705 p/u's in 70's when they were first built. I still have the round boxes they came, along with the wide and narrow mounting plates. One p/u had the single conductor with braided shield. Other had red and black leads. I called the Lawrence Co. to ask why, and they told me some were made each way, and were getting production set-up. I was assured they were same.

Never say never.

Thanx,
Jim

PS - these p/u are on my Super Pro and are great!

Jim Cooley · From: The 'Ville, Texas, USA

Don't apologize, Jim. Accurate info is always useful and welcomed. It also makes me feel better about the two I have with two leads, even though it looks one of them is really a 605. I appreciate everyone's input.

Jim Bates · From: Alvin, Texas, USA

Try the Forum for some of the small single conductor with BRAIDED shield. You MUST use a heat sink (small alligator clip or forceps can work) between soldering area and braid where it goes back into wrapped area to keep the braid from from getting so hot it can melt into the single conductor coating and cause a short. Use low wattage soldering iron, and small diameter solder. Use electrical tape to wrap the splice.

Thanx,
Jim

Bob Lawrence · From: Beaver Bank, Nova Scotia, Canada

I posted an original 705 speck sheet here:

http://bb.steelguitarforum.com/viewtopic.php?p=1655770

Jim Cooley · From: The 'Ville, Texas, USA

I had an interesting conversation with Jerry Wallace. He confirmed that since the resistance reading on the pickup in question is equivalent to half of what it should be (10k Ohms vs. 20K Ohms) there is most likely a break in one of the wires, so I'm only getting a reading from one of the two coils. Anyone who has ever taken the base plate off a 705 knows that the chrome surround is really the pickup's housing. Everything is mounted inside. After all the components were placed inside the housing, the pickup was filled with epoxy resin. The guts aren't coming out in one piece. This makes it impossible to repair. So, a pickup like this one can be used for whatever the imagination can concoct, except a guitar pickup.

Regarding Lawrence 705's with two wires vs. five wires, Jerry told me that there are original 705s having two, four, or five wires. They're the same pickup inside. It's just that for some reason, the manufacturer made the connections internally on some of these pickups and externally on others. He also said that temperature can affect resistance readings dramatically.

I bought these original 705 pickups for a new build. I have one good 705. The one that reads 16.4 Ohms is a 605 instead of a 705. I'm wondering how much of a difference it would make if I installed the 605 anyway. I realize the I would likely hear accentuated highs, but is it anything I couldn't compensate for with EQ? What if I install the 705 on the E9 neck and the 605 on the C6 neck? I think I'll start a separate thread.

Thanks again for everybody's input. Where would we be without this forum?

Craig Baker · From: Eatonton, Georgia, USA - R.I.P.

Jim,
Interesting thread. Looking at the ad link that Bob Lawrence posted, they state the impedance of the 705 is 96,000 ohms at 1,000 Hz. Common engineering practice is to present a load of at least 10 times the output impedance of a device. That would mean that all of us using a 500,000 ohm pot in the volume pedal are overloading the pickup "right out of the gate". The 705 should see at least a 1,000,000 ohm load. Since the pickup is inductive, as the frequency goes up, the impedance probably goes up also, until it peaks at the pickup's self-resonant frequency, then begins to drop off.

As far as your meter reading 10K ohms rather than the published 20K, I would think you may have a partial short rather than an open winding. Either way, it may not hurt the sound of the pickup. It might sound great, it might not. You never know until you try it.

I've had a 705 since the early '80s and it has one small coaxial cable, just a shield and signal wire, and it sounds . . . OK

Let us know how it sounds if you try it.

Best regards,
Craig Baker 706-485-8792

cmbakerelectronics@gmail.com

C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024
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Alan Finch · From: California, USA

can you take a part the L-705
pickups

Jim Cooley · From: The 'Ville, Texas, USA

Alan,

According to all the information I was able to obtain, the inside of these pickups is filled with epoxy resin, so the internals won't come out without destroying them.

Bill Quinn · Posted 26 Jul 2022 8:49 am

I had sent a non-working chrome 705 to Lollar a while back, he said they are not repairable.

I’ve seen 3 or 4 different wiring schemes on these pickups and all are original.

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