My brother and I have build two 6C33 SET (single ended triode) 15 Watt Class A amplifier. This is a very nice amplifier with a very pleasant warm soft sound and you don't get tired listening to the amplifier and ee are very pleased with the finished result.
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The inside of my brothers amplifier. Notice the placement of two signal cables, we had to do some trail and error to minimize hum. We have placed the amplifier pcb's in the corners and the signal cables make a loop, but it is possible to balanced out the hum.