How far apart to keep guitar pickups and transformers?

It's not really a problem. If it were, the magnet in a combo amp speaker would be hoop-a-jooped.

Transformers conducting AC can have a degaussing effect on magnets, but they have to be right up against each other for that to happen. Storing pickups with unused transformers is just as safe as storing pickups with donuts. Except don't dunk your transformers in your coffee.

Dropping or banging on a pickup can damage a magnet and sometimes even reverse its polarity....and the coil wire on the bobbinare more fragile that human hair. So handle pickups gently. Wrap them in paper and tape it closed to protect 'em when storing; don't leave them loose and rattling around in a box or bin.

 

Why do you think you never see transformers in the same display case with pickups in guitar stores?

 

were it true ...potentially propping your guitar against your amp would harm it...it doesnt...unless you fall on it

 

But hoop-a-joop can still happen for no apparent reason.
So be careful, if you ever suspect or even sense that
Hoop-a-Joop may be present, don’t turn it on until you get it sorted out, it’s not worth the risk.

 

no risk of Hoop-a-Joop if you got them directional cables. . .

 

The great late Bill Lawrence has mentioned magnet life and how to treat them. Course he did not mention the common transformer pickup display cabinet.

http://www.billlawrence.com/Pages/Pickupology/magnets.htm