Ampex developed a number of vacuum tube circuits that have stood the test of time and can be instructional.   The 351 reel-to-reel tape recorder had an amplifier stage which is effective and very good sounding.  It is used even today in a number of very successful audio mixers and preamplifiers. 

CineMag analyzed a number of the original Ampex output transformers to develop the CM-351.  It is a replacement with enhanced performance to meet modern standards without compromising the sound characteristics of the best of the original exemplars that were analyzed while developing it.  Another CineMag transformer, the CM-9600T, also works in this circuit providing even higher performance than the original.