Old LC-50 Mk 1 problems

Jimmy74
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Joined: Thu May 24, 2007 6:56 pm

Old LC-50 Mk 1 problems

Postby Jimmy74 » Sat Sep 27, 2014 8:28 am

I'm having some strange problems with a first version LC50, recently retubed and biased (following indications shown on the LC50 series II schematic= - 41V for 5881 tubes). I also replaced the speaker cable and mains filter cap. The problem is the following, amp turned on and standby off, nothing attached to the input everything seems normal, playing around with volumes no strange noises. However once I attach the guitar, on both channels, going passed volume 2 I get a constant noise hum, like when you touch the tip of a guitar lead. I've tried different guitars and guitar cables, the problem is always the same, also on both inputs of the amp. First question, any ideas? Preamp tubes are new too, only the PI tube was left original. Second question is the series II schematic a reliable source for the series 1 circuit?

thanks

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