KT120 transformer failures

With the KT-120 it is strictly an issue with the filament supply.

Pretty much every KT120 sales spec/note/description including the "official" one from New Sensor has that "tube heater current filament supply or" warning. I stand warned. Audio Research along with a bunch of other amp builders have modified their transformers to handle this issue and I still had to ask...is there a melted amp someplace? I bias the KT120s to the Jolida 500mv specs (I use a voltmeter even though the Jolida "ez bias" LED thing works fine) and the KT120s sound significantly stronger in every way over the otherwise fine stock (also Tung Sol) 6550s. I even talked to Kevin Deal at Upscale Audio and he said the KT120s are selling like hotcakes and he's never heard a customer mention an actual transformer overload issue...so much for my little research project.

Hey Wolf

I can't help you answer your query but maybe the gents over at Conrad-Johnson can. The CJ Classic Sixty SE Amplifier utilizes KT120 tubes throughout. Maybe they saw the current draw issue you speak of and overcame it. From stuff I've read about them they are really good people over there and who knows they may be willing to chat with you about the KT120 transformer issues.

Info about the Classic Sixty SE.

http://www.conradjohnson.com/It_just_sounds_right/Classicsixtyse.html

Luckily there seem to be NO transformer issues with the 502P. Not yet anyway, and I assume if it was gonna die it would show some signs of impending failure. My trusty warranty is there just in case. The CJ "SE" is on a price level that begs comparison to "things that interest me" like the Cary 120SII, Audio Research VS 115 (now with 8 KT120s!) McIntosh MC275, and other stuff, but the Jolida sounds so damn good and provides me with the requisite space heater and tube glow features that apparently I now need, so I'm content with it. At around a grand new there's not a lot out there that compares.

The newer ARC products have been designed with higher current ratings on the filament winding expressly for the purpose of using the KT-120. A few earlier ARC pieces, by virtue of their robust filament windings can also take advantage of the KT-120's. There are other ARC amps that can never use this tube do to issues where the length of the tube creates issues, i.e. cover will not go on or transformer in the way.