[Vintage-Audio] VERY SPECIAL 'lytic cap in Scott LK-72

[Phil]

Hello Again.

I just thought that I'd mention, that while working on this amplifier I have
discovered a VERY special capacitor in this unit.  IF anyone recaps this
beast, BEWARE.  (No I didn't replace it so I had no problem with it).

In over 45 years of working on Radio equipment, EVERY FP type Can
Electrolytic capacitor that I can remember has the metal can as the COMMON
NEGATIVE.  If they needed to have a Negative Voltage, they 'floated" the can
above chassis potential and put an insulating sleeve over it.

Well, Scott needed a negative supply Voltage for the Bias circuit and the
pre-amp tube filaments.  So, for capacitor C203 they apparently had a
special capacitor built for them.  This critter is a Quad section
100uF/75VDC FP Can capacitor in which the CAN IS COMMON POSITIVE!

SO, if anyone re-caps this critter make sure that you observe correct
polarity as you CANNOT assume anything here.  You can use small axial lead
caps below the chassis, just don't assume the can is negative, 'cause IT
AIN'T.

Just thought I'd pass this little tip on, perhaps everyone out there already
knew this but it's better to be safe than sorry.  If you're like me, you
really hate that "big bang" and then the job of digging all that foil out of
the innards of a piece of gear 8^(

73 de Phil  KO6BB