I have a transformer that has six wires which has been removed from the circuit .while the 2 primary wires have voltage of 110 the two secondary shows 300v and the last two shows 12v.is this enough info to determine if this is a good or bad transformer.this is a 3 tube amp with 700acv 12.6 filament.this is all I can come up with.
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Transformer question.
- Thread starter Hicountry
- Start date
For the most part, if you power up the primary and don't get smoke or a loud grunt sound that means it's not blown up.
Checking each winding for continuity can be done with the low voltage from a multi meter's resistance measurement. Safer than live-voltage tests.
To check the high-voltage winding for leakage to ground, normally you would ground one (usually) red wire only, leaving the other one safely taped on the end. If there's an insulation fault on the high voltage, this tends to expose it. This is pretty much the only other thing that could go wrong besides a dead-shorted winding.
Just one problem. If you don't have a variable-voltage AC supply to turn it up slowly, an incandescent light bulb in series with the primary will limit any potential fault current. The bigger the bulb's watt rating the better. Can't just buy a 200-Watt household bulb any more. I suppose you could put three 60-watters in parallel, maybe?
Once the primary is powered, checking the 12.6-Volt winding for proper output is worth doing. Expect as much as 10 or 15% higher voltage reading when there is no load current. At full load, it will typically drop back down the the specified 12.6.
73
Checking each winding for continuity can be done with the low voltage from a multi meter's resistance measurement. Safer than live-voltage tests.
To check the high-voltage winding for leakage to ground, normally you would ground one (usually) red wire only, leaving the other one safely taped on the end. If there's an insulation fault on the high voltage, this tends to expose it. This is pretty much the only other thing that could go wrong besides a dead-shorted winding.
Just one problem. If you don't have a variable-voltage AC supply to turn it up slowly, an incandescent light bulb in series with the primary will limit any potential fault current. The bigger the bulb's watt rating the better. Can't just buy a 200-Watt household bulb any more. I suppose you could put three 60-watters in parallel, maybe?
Once the primary is powered, checking the 12.6-Volt winding for proper output is worth doing. Expect as much as 10 or 15% higher voltage reading when there is no load current. At full load, it will typically drop back down the the specified 12.6.
73
Okay, shoulda read for comprehension. You already powered it up and it behaved okay, right?
If the amplifier required a 700-Volt winding for the B+ voltage, this tells us the rectifier is a full-wave bridge circuit.
You can use a transformer with half the voltage by using a full-wave voltage doubler circuit instead.
Might be easier than it sounds. If it uses two filter caps in series, that makes it easy. And if it has three filter caps in series, not quite so easy.
Then again, if the old filter caps are original, they need to be replaced because of age alone. You could put two 500-Volt rated filter caps in series. One side of the transformer would go to the point where the two caps are connected, the "midpoint" of the pair. The other transformer wire would go to one of the AC inputs of the bridge-rectifier circuit.
73
If the amplifier required a 700-Volt winding for the B+ voltage, this tells us the rectifier is a full-wave bridge circuit.
You can use a transformer with half the voltage by using a full-wave voltage doubler circuit instead.
Might be easier than it sounds. If it uses two filter caps in series, that makes it easy. And if it has three filter caps in series, not quite so easy.
Then again, if the old filter caps are original, they need to be replaced because of age alone. You could put two 500-Volt rated filter caps in series. One side of the transformer would go to the point where the two caps are connected, the "midpoint" of the pair. The other transformer wire would go to one of the AC inputs of the bridge-rectifier circuit.
73
Maybe a 750 watt bulb?
I can't leave this picture up long, these things are considered contraband now days.
73
Jeff
That one's too big to serve as much of a current limit. Definitely an endangered species.
73
73