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RE: Rugged, good sounding KT 88 for Quad II forty

It is a Quad II forty designed by Tim de Pavaricini for Quad and they sell boatload of them (relatively) I've read some reports of blowing tubes in that amp. It has cathode bias with quad cathode feedback trough separate OPT winding. The anode tension is 390-400V and cathode resistor is 390 Ohm 6W . I measured bias and its 39V so the tube draws 100mA which makes 39-40W dissipation rate. The creeping bias issue follows the tube. I think slightly undersized cathode resistor (6W) acts as a fuse , it just burns out. I called Quad and they recommend Sovtec.They said GL should be fine and maybe it was bad batch but you know, with price of those my friend is not willing to risk. I wonder if the tube with creeping bias would be just fine in the amp with fixed bias and cooler operating point. Personally I'd just put 470 Ohm in cathode but you know the audiophiles and their cherrished gear.


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