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View Full Version : Weird taps and color coding on old geezer OT?


vibroverbus
06-11-2009, 12:12 PM
Continuing on previous threads about this old PA amp project...

More confusion and distrust on my side vs. the old wiring so I measured up the wires on the OT and get the following DC resistances and am interpreting the following taps (all assuming Black = GND)

Yellow .5ohms = 4ohm tap
Green .7ohms = 8ohm tap
Orange 1.3ohms = 16ohm tap
Red/black 50ohms = ??

Although I thought green/yellow were usually in the opposite order on these old magnetics I'm assuming this is the code as the resistances seem approximate for std. OT stuff. But can anybody tell me what's the red/black tap for?

The PA circuit that was in there seemed to be running the speakers from the green tap and using the yellow tap to supply NFB by the way (and previously the Orange and that weird R/B tap were both taped off)... don't think I'm going with any NFB as this is really a tweed-type amp.

http://www.j2c3.com/misc/IMG_0391%20(Small).jpg

Tonic Amps
06-11-2009, 12:50 PM
The red/black was probably the 70v tap used in older equipment, but is archaic today.

teletroy
06-12-2009, 02:51 PM
+1 on the 70v tap especially if it's from an old PA.

vibroverbus
06-12-2009, 07:20 PM
huh! OK yeah that makes sense I guess. wunna thought of it. THannks!