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Old 17th Jan 2008, 8:52 pm   #17
Ed_Dinning
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Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Quad 2 Valve power amp questions

Hi Paul, on some potted transformers like the Quad the connection will go to the screen and posssibly and earthed heater line as well before exiting the can. This appears to happen in your case. It is probably not a good idea to fuse this point as if the fuse goes due to a fault, then a highish voltage may be imposed across valve heaters to cathodes.
It could be worth reducing the size of the mains fuse to 1A or even less as long as you use a time delay/ anti surge type; otherwise you may get fuse blowing at switch on due to surges. Try measuring the input current when running at full power, this will be an indication of the current the fuse will se in use.
The HT centre tap fuse is used because there are some faults that can cause the transformer to burn out, but not draw sufficient current to blow the input fuse.

Ed
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