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RE: KT-88 bias in MB-3045

Posted by elektron on June 18, 2009 at 20:10:59:
Jerry, hi again. Caucasian Blackplate and Chris O have good advice. But, I think you are up to speed on bias setting. I did my 3045 triode - g2 tied to the plates with a 100 Ohm R as I recall. I think you are correct on the RC time constant network being for what Lux called 'Ultra Linear' although obviously a misnomer. My 3045 documents are at another location as I write this. The so-called 'UL' operation was merely putting some B+ on g2. Obviously there are no Ultra Linear windings. One of the reasons the stock amps sounded so good was the output tubes were being run on the threshold of thermal runaway. Jeez did they get hot. The NEC made for Lux 8045G output tubes appear to be internally triode connected horizontal output tubes. G2 is tied to the plate, beam plates connected to the cathode. 485 V is B+ to the finals. Funny, I never had my amps sound shrill. As you say probably the kind of KT-88 and bias. I would like to see exactly what Futterman did on them. The 6LF6 is probably closer to what Lux had NEC gimmick up than either 6550 or KT-88. On the other hand, if you are going to run same at 75 mA I'd be prepared for early failures much in the pattern of the original 8045G fiasco. Sorry it took so long to post a reply. Turned out to be a much busier day here than anticipated. Shoot me your phone number via AA e-mail and I'll try to phone over the weekend. Let me know when it would be convenient to call. I have toll free in CONUS. These amps can be a challenge with typical one inch deep chassis. Still, there are things that can be done and some that must be done. Ultimately unless Nichicon decides to make a double 220uf at 550 and another triple whatever at 550 WVDC re-do of PS electrolytics is impossible without outboarding