Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: attilio on May 01, 2012, 09:29:25 pm
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my ab763 with a bridge rectifier keeps blowing fuses and only when i connect the red -red AC to my rectifier. i disconnected everything else past the rectifier to eliminate a short in b+, and i tried 3 other new 3amp 1000V rectifiers. pilot lite is on and ac voltage across red to red is good 720v without recifier. if anyone can offer advise to help me wrap my head around this problem it would be much appreciated. it's a vibrolux but when i got it there was no pt in it, so i used a bandmaster pt which didnt have a tube rect. worked good for over a year until last week.
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Center tap grounded. Some were soldered to the chassis. I have had the soulder break loose and cause fuse to blow. Reconnected it to a PT transformer bolt.
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I don't recall any AB763s that used a bridge rectifier. My TRRI uses a bridge but I don't know if that qualifies as an AB763. Exactly which amp do you have? Is it a factory built amp or a home brew? If homebrew, has it ever worked? Can you supply a schematic? Does it still blow the fuse with everything past the rectifier disconnected?
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it's a vibrolux but when i got it there was no pt in it, so i used a bandmaster pt which didnt have a tube rect. worked good for over a year until last week. still blows fuses with b+ diconnected.
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Every bandmaster I can find that uses ss diodes uses 6 diodes wired in a full wave conventional rectifier circuit. None of them use a bridge. A bridge is composed of 4 diodes and may be a single component with 4 terminals. If you have a true bridge, don't connect the negative terminal to chassis. You only need to use the two AC terminals and the positive terminal on the bridge. That bandmaster PT has a center tap that should be connected to ground and if you connect the negative terminal of a bridge to ground, you effectively short out the HT windings and will blow a fuse.
Maybe I'm just not understanding exactly what you have. A picture is worth a thousand words.
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and a lamp limiter is worth a thousand fuses. Just sayin......
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thanks sluckey! that was it, i grounded the the bridge recently and thats when it started happening. sorry for the silly mistake, my knowledge is limited.