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Old 19th June 2006, 07:11 PM   #1
Carlp is offline Carlp  United States
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Join Date: May 2006
Location: A New England
Default Transformer center tap connections

I'm working on a small SET by Fred Nachbaur (the Miniblock,, mostly a simple but pretty cool design and construction, but I'm confused about the power transformers. He specs two power transformers (120V to 12 V) with the 12V ends connected. The 12 volt section supplys the heater and the "C" supply for the power "tube" grid. The second power transformer then steps voltage back to 120 and provides the B+ voltage (about 215V with a voltage doubler).

My trouble is, the transformers come with center taps on the secondaries that are unused as far as I can tell. So what to do with them? They are at zero potential relative to the 12V AC coming from the secondary windings, but I assume I can't just let them hang out. Cap them? Something else? Or have I misread the circuit?

Can anyone help me out? Sadly, Fred is no longer able to help us budding DIYers with his circuits.

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Old 19th June 2006, 07:19 PM   #2
Merlinb is offline Merlinb  United Kingdom
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Yes the centre taps are not connected to anything, just make them safe. Either cut them short and shrink-wrap them, or coil them up and shrink-wrap them, if you think you'll use the transformers again one day.
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Old 19th June 2006, 10:01 PM   #3
Carlp is offline Carlp  United States
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Join Date: May 2006
Location: A New England
Thanks, Merlinb. I thought that was the case. I expect to one day use the transformers again, so I like the coil and shrinkwrap idea.

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