[HAM] PR-40 hum

[Keith Cary]

Please, please trim your posts. It makes it really hard to get to the  
actual question.

If you do indeed need a transformer you might check out  Edcor. Their  
transformers are reasonably priced and they do custom work. Or, if  
the list thinks a 600 ohm to 600 ohm transformer would work, you  
might be able to use one from All Electronics. They cost a dollar.  
$1.00. I'm guessing the fidelity will be good enough for a Hammond  
spinet. For a dollar it's worth a try. The one I have in mind is CAT#  
TCTX-13. the catalog is available at www.allelectronics.com. They are  
small signal transformers and can't handle much power at all.

Am I right in remembering that the L112 is a spinet? If so, then  
isn't an output taken off a speaker a balanced output already? I  
believe it isn't tied to chasis ground so is floating. You'd just  
need four resistors to bring the level down. If you're interested in  
that, I'm sure someone here can give you those values.

However, I have my doubts that the problem is actually the balanced/ 
unbalanced thing. It can certainly be troublesome, and it wouldn't  
hurt you to put in a transformer in to make it right, but if the rest  
of the PR-40 is working fine and it is just humming with the treble  
reverb turned off I'd be looking elsewhere for the problem. I think I  
had a similar problem with a PR-40 and I finally found a bad cap on  
the treble side. Those things are a bear to work on with those  
circuit boards that stick up at a 90 degree angle. It sounds to me  
like if it's humming with the reverb turned off, then an output from  
the reverb is being left ungrounded, acting as a perfect 60 cycle  
antenna. Check the switch. -- This is just a wild guess, but I don't  
think it would be a black smoke and ambulance moment: try ground  
ingthe signal output of the reverb spring. Just use a clip lead from  
ground to the output of the reverb spring. You might wait until a few  
real techs see this, but I don't see how it could hurt anything.

Keith