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amp decision

Bigromano, hi. Not familiar with the SF2se. Is it single ended? I remember most of their stuff as being push-pull - kind of text book designs. The Snappers from Manley are 6BQ5 amps if the memory is working. It is difficult to find bad sounding 6BQ5 amps. Something about the 6BQ5 tube itself I guess. I would put the 7591/7591A in the same group. I would tend to favor the Snappers in this pairing. Now for the MB-3045 Luxman amps. Stock they use 8045G - an NEC triode connected horizontal output tube with laminate plate metal and extra radiation wings to dissipate heat. There is no reliable source for these tubes on the planet. Lux ran them at 75mA! at 485V B+ - right under thermal runaway. Often they ran away. This proved disastrous for Lux America. Lux would replace the first set of output tubes under warranty. Then you were on your own. Lux sent out a modification for 6550/KT-88 either triode connected or what they called "Ultra Linear" which was not. The screen was simply provided B+ via a dropping resistor so screen and anode voltages were different. Also Luxman used another (!) proprietary tube - the 6240G which is described in Japanese literature as derived from a 12BH7. The direct substitute for 6240G is a 6FQ7. No modification needed here. Just plug it in. Now to the other problems. It has been 20+ years since these things were made. Time to replace all electrolytic capacitors. But - the caps are rated for 550V DC continous not surge. Try and find 550V dual and triple section electrolytics! I suspect these things were also a custom order through Nippon Chemicon. If you choose to upgrade the original mylar couplers you will discover the last pair of couplers are rated to 1000V DC. This is not a mistake. You will also find no spare room under the chassis. Unless you have the patience of Job and enjoy making spatial relations decisions in millimeters you will be confounded. Now - on the plus side - the amps sounded glorious when they were working with 8045G. The original NEC had beaucoup problems. The later reissues made in China were even more horrible. I had a pair of Gold Aero's last all of 2 minutes before thermal runaway. The new tube warranty was not honored. There were other mods: Futterman 6LF6 (try to find good ones now!) and EL34. At least the 6550 would give more power then EL34. Even with 6550 output power is reduced. Looking at the curves of the 8045G Lux was running them balls to the wall. They did the same thing with those "triode" amps they made that used 50-CA10 - needing 50 volts for the filaments(!). The circuit reflects the McIntosh Unity Coupled Circuit somewhat except the primaries in the output are quadfilar. I own two pair of these amps. One pair is for parts.
I love the sound of them, but you have been warned. Are you handy with a soldering iron? Have you worked on tube amps? If the answer to either of these questions is no then another choice is indicated.



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  • amp decision - elektron 07/26/0708:35:53 07/26/07 (0)

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