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  • Isolation Transformer Upgrade for Old Guitar Amps

    Damn. I wish I scoured these comments a little closer back when I was ordering parts. The Kay 703c is the same amp that I have been using this instructable for. And I've spent the last couple days scratching my head trying to figure out that rectifier issue.I have one quick question first. The 703 is a 33W (consumed) amp. Would a 100VA iso be enough to handle the half wave issue?This my first real tube project (not counting a kit), so I am a little green. The data sheet for the 36AM3 says that the heater tap (pin 6 where AC is connected) is meant to be used as a current limiting resistor and that it has a resistance of 45 ohms when the output current is at it’s max. That could be what you were saying already (3 years ago), but I just wanted to pass that along in case it makes that...

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    Damn. I wish I scoured these comments a little closer back when I was ordering parts. The Kay 703c is the same amp that I have been using this instructable for. And I've spent the last couple days scratching my head trying to figure out that rectifier issue.I have one quick question first. The 703 is a 33W (consumed) amp. Would a 100VA iso be enough to handle the half wave issue?This my first real tube project (not counting a kit), so I am a little green. The data sheet for the 36AM3 says that the heater tap (pin 6 where AC is connected) is meant to be used as a current limiting resistor and that it has a resistance of 45 ohms when the output current is at it’s max. That could be what you were saying already (3 years ago), but I just wanted to pass that along in case it makes that circuit make a little more sense. And one more question (sorry if it’s answered somewhere else), that standing DC voltage that occurs, is it causing the iso to use more power? Or are we just overrating the iso to deal with extra heat? It seems pretty straightforward in step 8, but since I am tube green I just wanted to be crystal clear exactly how you meant that.Thanks for the instructable. This has been fun, if a little frustrating. And time consuming….Cass

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