tube amplifiers-en-gb

Finally the work on his pair of amplifiers is done. Let's have a look on what's different..

 This is the new look. The places that use to hold UTC chokes are replaced by load-inductors and interstage transformers.

Vacuum tubes have been invented for nearly 100 years. Honestly all possible circuits configurations are almost exhausted. About fifteen years ago, following the rise of internet, there used to be an electronics Periodical called theTube CAD Journal where many innovative circuits were published. Tube CAD Journal seems to cease publishing since 2003. Around the same time period another paper based Periodical, the Vacuum Tube Valley, stopped publishing after the chair editor Charlie Kittleson passed away. There were a total of 20 issues of Vacuum Tube Valley with good materials on vacuum tube circuits. Since then it was really quiet. That's why my eyes were wide-open when I see the Longitudinal Direct Couple Amplifier. In the rest of the article I use the acronym LDCA to represent the name of this circuit.



Longitudinal Direct Couple Amplifier, publish granted by Chris Strickland


This pair of 50 SE amplifiers was built by me some 15 years ago. The circuit is very stable and during the years of service there wasn't much problem except one event 3 years ago. The problem was caused by one faulty 80 rectifier where the filament broke and fallen onto one of the plates. It caused a short-circuit from the high-voltage winding of the mains transformer to the ground. I was using a 3A fast blow fuse and the short-circuit current caused by the faulty rectifier wasn't high enough to blow the fuse. Consequently the transformer heated up and eventually blew up the winding. The transformer was carefully built by James Audio but apparently it can't withstand such high current for a long time. Ever since that event I became extremely cautious about safety. If you ever built a tube amplifier, ask yourself a question whether or not the amplifier will survive when a rectifier goes to short circuit. This is a common problem for the rectifiers with hanging filaments. And many people including me believe tubes with hanging filaments sound better.

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Telefunken EL-156 Single-ended amplifier