[HAM] Unexpected resistance

[David Anderson]

I thought I'd post something I've run into several times over the  
last year as I've been doing maintenance on my Leslies.

What I've found is resistance in the various contacts between the  
amplifiers and speakers in the  1-10 Ohm range.

Examples:

145 cabinet: 1.5 Ohms resistance between the wire and the push-on  
terminal to the horn that was solved by cutting off the old terminals  
and crimping new ones on. Re-crimping the old ones wouldn't do the job.

44W cabinet: heavy corrosion on the horn socket in the crossover not  
easily visible from the outside. Cleaning with metal polish did the  
trick and restored full signal level to the horn. It *sounded* a bit  
like a buzzy horn, but it wasn't.

F15LL speaker plug: I read widely varying resistances between the  
plug and the voice coil terminals on the frame until I hit the pins  
with metal polish.

Noxon is my favorite metal polish for this kind of thing. DeOxit is  
good, but it doesn't always cut through heavy layers of oxidation.  
Noxon also does nice things for the pins on your Leslie cable if  
they're looking grungy.

I don't want to start a huge discussion/controversy. All I want to  
suggest is that if you've got your Leslie open for some kind of other  
service, you might want to check to see if you find any resistance in  
the speaker/crossover wiring that shouldn't be there. I've been  
surprised to find it in as many places as I have.

I should note I've even found the same thing inside expensive KEF hi- 
fi speakers from the 1980s. Of course, you'll need to READ YOUR  
SCHEMATIC and understand that there's a coil (with normal resistance  
in its windings) in series with the woofer and a capacitor in series  
with the horn such that you shouldn't find any DC path to one horn  
terminal. I guess it means I'm getting old, but my patience with  
people who post before doing their homework is a diminishing  
resource. And yes, your digital multimeter will probably read .3-.4  
Ohms even if you touch the probes directly together :)

David A.