Fender Transformer Problem

MstrB · 10-29-2009, 06:08 AM

Here is a new one. I have a Fender Bandmaster output transformer that reads 175 blue to red, 48 blue to brown, and 48 brown to red DC resistance. Is that strange or what.

melvin · 10-29-2009, 06:57 AM

I think you mean, is that even possible? Are you sure you checked that correctly?

MstrB · 10-29-2009, 07:27 AM

checked it 3 times to be sure. Been doing amp repair/builds for a couple decades, first time I have come across this.

melvin · 10-29-2009, 07:31 AM

I assume it was hooked up with red to HT? Maybe the wires are miscolored. Try putting a sinewave across the secondary and see what shows up on the primary.

Enzo · 10-29-2009, 10:34 AM

Is it still wired into the circuit? And just for fun, did you take the readings again with your meter leads reversed? That is, reversing the polarity of the small current your meter uses to read resistance through the winding.

The only thing that sticks in my mind is shorted turns, but I am having a hard time wrapping my head around a scheme to get those results. Imagine three terminals R, Bu, Bn, and make up a resistor array between them that yields those results...

So in my cloudy imagination, I see some sort of short between the blue and brown windings such that the meter current partially bucks itself resulting in the odd reading. of course it could be totally something else.

Go over to RG's Geofex web site and look up his little transformer tester. It checks for shorted windings, and is simple to make.

Are we to assume further that it doesn;t work well in the amp?

10-29-2009, 06:08 AM	#1
MstrB Junior Member Join Date: Jul 2008 Posts: 13	Fender Transformer Problem Here is a new one. I have a Fender Bandmaster output transformer that reads 175 blue to red, 48 blue to brown, and 48 brown to red DC resistance. Is that strange or what.

10-29-2009, 10:34 AM	#5
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,366	Is it still wired into the circuit? And just for fun, did you take the readings again with your meter leads reversed? That is, reversing the polarity of the small current your meter uses to read resistance through the winding. The only thing that sticks in my mind is shorted turns, but I am having a hard time wrapping my head around a scheme to get those results. Imagine three terminals R, Bu, Bn, and make up a resistor array between them that yields those results... So in my cloudy imagination, I see some sort of short between the blue and brown windings such that the meter current partially bucks itself resulting in the odd reading. of course it could be totally something else. Go over to RG's Geofex web site and look up his little transformer tester. It checks for shorted windings, and is simple to make. Are we to assume further that it doesn;t work well in the amp? __________________ Education is what you're left with after you have forgotten what you have learned.

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10-29-2009, 06:57 AM	#2
melvin Member Join Date: Aug 2009 Location: Seattle, Washington Posts: 86	I think you mean, is that even possible? Are you sure you checked that correctly?

10-29-2009, 07:27 AM	#3
MstrB Junior Member Join Date: Jul 2008 Posts: 13	checked it 3 times to be sure. Been doing amp repair/builds for a couple decades, first time I have come across this.

10-29-2009, 07:31 AM	#4
melvin Member Join Date: Aug 2009 Location: Seattle, Washington Posts: 86	I assume it was hooked up with red to HT? Maybe the wires are miscolored. Try putting a sinewave across the secondary and see what shows up on the primary.

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