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RE: KT120 tubes in Luxman MB3045?

tutor turtle, hi. I too have Luxman 3045 and have been thinking of doing this. Each 3045 output tube filament winding is rated to 2.5 A and the 8045G pull about 2A. KT-120 draws almost 2A per tube so from this standpoint you are home free. Published specs show 120 filament current draw from 1.7 to 1.95 A. Lux B+ is 485. KT-120 shows plate V DC design max 650V and grid 2 triode connected 600. This looks good too. Cathode Current limits are 250 mA pentode connected and 230 triode. It looks like everything is a go. There is something else you should consider. Regardless of output tubes the electrolytic caps in your 3045 are going on 30+ years old. Every time you turn on your amps the first electrolytic section gets whacked with full B+. As old as the caps are there will be a time when it will fail most likely as a dead short. This could have catastrophic consequences. If you are 'lucky' the main fuse will blow. MB-3045 owners must contend with this reality. Unless you turn the amps on with variac every time you switch them on you are playing electric Russian roulette. Also there are other electrolytics in them that should be replaced. You could use a thermistor to slow inrush. Still the electrolytics are aged and have been pounded every time you turn them on- the first section in particular. You could reverse the sections. Put about 30 Ohms in series with the first section. Though mainly a SET guy the MB-3045 Luxman are special. Mr P. hit a home run with them. I am considering (A). separate chassis with power supply and bias supply C or (B) building composite caps to fit spaces on the amps without the hassle of second chassis.


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