T Top with sound and NO reading... An explanation?

[freefrog]

Hi,

I've here a SG built in the early seventies, with 2 T Tops. The covers have been pulled off a long time ago. The bridge PU has been modified: broken legs replaced by two pieces of aluminium (!).

The neck PU is normal: 7,4k, 3,9H.

The bridge PU has NO DRC nor inductance. My multimeter stays dumb... or shows absurd readings (1690MOhm).

When I play it, it has a robust output level but a strange tone. As if the coils were out of phase and splitted in the same time. Picture of the frequency response below...

I suspect a short cut in the slug coil as the screws coil has normal specs.

How can a pickup sound loud with a short cut in it? Mutual inductance? Something else?

If someone could help me to understand, at least, I'd be grateful... And I wonder how I'll repair it for the owner of this old lady SG.



EDIT - I know that some people have already experienced the same thing. Sorry if ever I resurrect a dead horse.

Beyond my desire to understand, I'm also searching a solution other than changing or rewinding the pickup... Of course, I can talk to the owner and tell him that EVH had such a dead coil in his main guitar on his first album... but it frustrates my honesty.

[David Schwab]

You have an open coil. The windings are capacitively coupled, so it still produces sound, but you can't get a DC reading on the meter. Often pickups like this sound very thin, but not always.

You can think of it as the tone you would get running through a small value capacitor.

[freefrog]

You have an open coil. The windings are capacitively coupled, so it still produces sound, but you can't get a DC reading on the meter. Often pickups like this sound very thin, but not always.

You can think of it as the tone you would get running through a small value capacitor.

Thx David! :-)

I was precisely thinking that the "bowed" bass range looks like the response of a Ricky PU through its cap... :-))

[the great waldo]

Hi David
And they hum a bit as well. But the best test is that the tone control does'nt work properly when the coil is open.

Cheers
Andrew

You have an open coil. The windings are capacitively coupled, so it still produces sound, but you can't get a DC reading on the meter. Often pickups like this sound very thin, but not always.

You can think of it as the tone you would get running through a small value capacitor.

[David Schwab]

But the best test is that the tone control does'nt work properly when the coil is open.

Right, the tone works like a volume.

[freefrog]

Yes, it's the case with this model: the tone pot acts like a volume. Diagnosis confirmed (anyway, once you had said it, I've found that idea absolutely obvious: my "tech brain" is not yet trained enough).

A big thank you, gentlemen!

Having to repair it with "local ressources", I plan to replace the bobbins with two coils coming from a Seth Lover... PE instead Poly and higher DCR but the "Q" appears to be the same... We'll see if my shameless tinkering of hobbyist works. :-/

Yours,

freefrog

[freefrog]

T-Tops repaired with the coils & baseplate of the Duncan.

Of course, it doesn't sound no more like a T-Top. but it's close enough and extremely satisfying. The Duncan parts bring a new vocal richness, giving an interesting hybrid.