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Richard's Stuff

This amplifier was inspired by Steve Bench's experiments with the Talema small power toroids as output transformers.  I built it in an empty Bombay Coy tea sampler box.

6AS7PP 001.jpg (85308 bytes)        6AS7PP 002.jpg (167621 bytes)

It produces 10W pc in class A, however, power at 20Hz is limited to about 4W which is not surprising.  I did not provide for balancing the current in the output triodes, simply used the best 6AS7s I had with respect to section-to-section matching.  The toroid used is the largest in the range, 50VA.  I would like to try something around 80VA, however at $17 each, the 50VA Talema units cannot be beaten for value as output transformers.  Furthermore, they are the only transformers I have tested which can reproduce a 20kHz square wave with absolutely sharp corners, no ringing or undershoot!  (I think square wave performance is an important aspect, so much of music has a fast attack or transient nature.)  Apart from the LF limitation, the sound is fine, full, detailed and fast.  I like it very much, everybody else who has heard it also likes it without exception (so far).  The 6AS7s being high perveance triodes, need protection during cathode stripping during turn-on.  I accomplished this by using a long time constant on the B+ regulation fets.

Click to see the schematic: