This 6550 two channel amplifier was reviewed in MJ March 1990.

Mr. Sakuma was surprised by the clear and powerful sound of this new method.
He found new music in his old records. He was assured that the tone of high performance LP and CD players, amplifiers and speaker cables is killed by a speaker crossover network.

After a few months, Mr. Sakuma wrote about a new amplifier in MJ August 1990.
This amplifier uses two kinds of output tube for several frequency ranges.
A single-end EL-34 is for the high frequencies and a 6550 push-pull pair is for the low frequencies.
Mr. Sakuma's amplifier showed us that the drive requirement for the tweeter and for the woofer is entirely different.
He then made new variations of the "two-channel" amplifier one by one. A feature of all of them is the single-ended output for high frequencies and the push-pull output for low frequencies.