Transformer nightmare!?!

metallifornia · 2nd April 2008, 04:22 PM

Hey all I need some tips! I am currently repairing a Randall RH100 and RH200sc. I have finished repairing the power section of the RH100 but I have 110ac on the B+?? It is a push-pull head using complimetary pairs of 2sc4793/2sa1837, 2sc1815/2sa1015 and 2sc5198/2sa1941 at the final stage. The transformer is 110primary to dual secondary 80VAC center tapped and 30VAC center tapped. I have already replaced the 1n5402 rectifier bridge completely with no effect. What is puzzling me is that the AC gets through the B+ side of the rectifier bridge at full cycle??....the diodes should clip half of that off... If there is short from the primary of the transformer to the secondary shouldn't the transformer output voltage drop signifigantly?? The real kicker is that I still have my + and - 40VDC after the rectifer???? ..................i have a headache!

-Brian

EnvisionAudio · 3rd April 2008, 07:14 PM

Quote:

Originally posted by metallifornia
Hey all I need some tips! I am currently repairing a Randall RH100 and RH200sc. I have finished repairing the power section of the RH100 but I have 110ac on the B+?? It is a push-pull head using complimetary pairs of 2sc4793/2sa1837, 2sc1815/2sa1015 and 2sc5198/2sa1941 at the final stage. The transformer is 110primary to dual secondary 80VAC center tapped and 30VAC center tapped. I have already replaced the 1n5402 rectifier bridge completely with no effect. What is puzzling me is that the AC gets through the B+ side of the rectifier bridge at full cycle??....the diodes should clip half of that off... If there is short from the primary of the transformer to the secondary shouldn't the transformer output voltage drop signifigantly?? The real kicker is that I still have my + and - 40VDC after the rectifer???? ..................i have a headache!

-Brian

Where is your negative DMM lead tied? To the secondary 0 volt point, I hope.

2nd April 2008, 04:22 PM	#1
metallifornia diyAudio Member Join Date: Mar 2008	Transformer nightmare!?! Hey all I need some tips! I am currently repairing a Randall RH100 and RH200sc. I have finished repairing the power section of the RH100 but I have 110ac on the B+?? It is a push-pull head using complimetary pairs of 2sc4793/2sa1837, 2sc1815/2sa1015 and 2sc5198/2sa1941 at the final stage. The transformer is 110primary to dual secondary 80VAC center tapped and 30VAC center tapped. I have already replaced the 1n5402 rectifier bridge completely with no effect. What is puzzling me is that the AC gets through the B+ side of the rectifier bridge at full cycle??....the diodes should clip half of that off... If there is short from the primary of the transformer to the secondary shouldn't the transformer output voltage drop signifigantly?? The real kicker is that I still have my + and - 40VDC after the rectifer???? ..................i have a headache! -Brian

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