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I've got a bit of an odd one here, it's got the normal blue, brown and red wires for the tube connections, and a black common, yellow 8ohm and green 16ohm. In addition, it's got an orange (4 ohm, maybe?) and two multi-color wires -- one is yellow/black, the other is red/white. This transformer squealed at certain volume levels when I tried to use it in an amp. Any idea what those muti-colored wires would be? Some sort of secondary center taps?
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Doesn't sound like a standard color code to me. First step is to Ohm them out and determine if the yel/blk & red/wht are part of the primary or secondary windings. (Maybe even a separate winding but I think that's unlikely) If you have a good Ohm meter you can determine a lot about the relationship stack up of an individual winding. Then you can drive one winding with an AC voltage and figure out the rest. What test equipment do you have available? -
The brown blue and red ought to be normal. Wire it up and connect a speaker to the black and yellow wires. It ought to work.. Oh if the impedance is wrong it won;t hurt anything, it will still amplify. If you have no NFB - negaqtive feedback - then the polarity of the blue and brown don;t matter. If you do have NFB, if you get them backwards, the amp will howl. WOOOOOO. In which case, swap the blue and brown wires.
Then what Tom said. Use an ohm meter to see what those extra wires are associated with. If they are part of the primary, I;d bet they are ultralinear taps for the screens. If they are separate windings, then it depends. Really old ones sometimes had a separate feedback winding. If this came from a PA amplifier, those could be 70v or 25v windings for CV distribution. If one of the wires seems to connect to nothing, it could be an internal faraday shield. Or perhaps a frame ground.
DO you know what the transformer came out of?Education is what you're left with after you have forgotten what you have learned.Comment
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The brown blue and red ought to be normal. Wire it up and connect a speaker to the black and yellow wires. It ought to work.. Oh if the impedance is wrong it won;t hurt anything, it will still amplify. If you have no NFB - negaqtive feedback - then the polarity of the blue and brown don;t matter. If you do have NFB, if you get them backwards, the amp will howl. WOOOOOO. In which case, swap the blue and brown wires.
Then what Tom said. Use an ohm meter to see what those extra wires are associated with. If they are part of the primary, I;d bet they are ultralinear taps for the screens. If they are separate windings, then it depends. Really old ones sometimes had a separate feedback winding. If this came from a PA amplifier, those could be 70v or 25v windings for CV distribution. If one of the wires seems to connect to nothing, it could be an internal faraday shield. Or perhaps a frame ground.
DO you know what the transformer came out of?Education is what you're left with after you have forgotten what you have learned.Comment
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Not sure what this one originally came out of. It 'works' when I tried to wire it up to an amp, but it just oscillates / squeals if the volume is taken up past 6 or so. I've tried swapping the blue / brown to see if it's reversed, and that really got it going, so I'm guessing it was right before (the amp does have NFB). It's especially sensitive as the treble knob is increased, and seems to be affected when the wires are moved around with a chopstick. The squeal is very high-pitched, like something that would make a dog quite unhappy. I wondered if any of those extra wires, which have been cut short at some point, needed to be grounded out... but I didn't want to destroy the tranny messing with that theory. Could the squeal also be caused by the primary impedence beiincorrect for the amp I'm trying this one out in?Comment
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There are many things that can cause unwanted self oscillation in an amp besides the output transformer.
I’d say no.Originally posted by cryptozoo View Post
There are your clues. The "it" in "it just oscillates" is most likely the amp as a system not the OT. You have not talked much about the amp yet. Tell us what it is. Is it a new build, stock production unit or modified? How old? Did it ever work correctly to your knowledge?Originally posted by cryptozoo View Post
Your problem could be caused by poor wiring dress, a bad ground connection, open filter cap, placement of the OT too close to some preamp circuitry or a number of other things.
Post photos of the amp if you can.
Later,
TomComment
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