You often hear about what are called "sleeper" amps. It's the same concept as the old "sleeper" automobile, the grandma sedan, that would pull up to a line beside something with a shiny SS badge and blow its doors off... Well, this is the very definition of a "sleeper amp". This thing will peel paint! Original ITT-labeled Mullard EL-84 output tubes in push/pull with cathode bias are good for about 15-18 watts of super saturated tube-overdriven power. A pair of 12ax7s provide two stages of upfront gain, one stage of phase inversion, and there is also a tremolo, which works by varying the output bias for a very natural, sweeping, dynamic tremolo.
Gregory amps are little known today. Like vintage Danelectro and Sano amps, these were made in New Jersey and were sold through numerous wholesale distribution centers throughout the country. Also like Danelectro, they made a few other house brands for other companies. This same practice was going on in Chicago with Valco and Lectrolab, among others.
Gregory amps were marketed to the beginner and intermediate player mostly, but they also made "professional" amps and PAs. Some of their designs were very unusual and it's safe to say probably didn't sell too well at the time, judging from their lack of prevalence.
This model, the Mark X, shares similarities in circuit design as some of the early, simple Marshall and Vox EL-84 based amps. The chassis is cheaply made, but other than that, it's right on. PTP construction with terminals, good-sized transformers, real BIRCH plywood (not some cheap particleboard), and this one has a later EV 12" speaker with a massive ceramic magnet. All this adds up to a very high quality "sleeper" amp that will blow the ever lovin' doors off of any PCB-constructed, Chinese-made, shiny thing passing for an amp these days.
This rare example has just been serviced and is ready to rock - 3-prong cord added, death cap removed, coupling caps, and power supply resistors have been replaced.