cdfac: I own one of the RGR model 5 amplifiers, along with the matching preamplifier. If the amplifier is working presently, I strongly advise you to avoid getting into it, as you are sure to regret doing so. This amplifier is excruciatingly difficult to work on. First, there is absolutely NO service information or support available. There are NO component designations on the circuit boards. Each amplifier circuit board was individually tweaked by the manufacturer's technicians. In other words, they are NOT identical to each other. MAJOR chassis disassembly is required to get at the soldered side of the circuit boards as they are totally inaccessible without doing so. The output stage is merely Quasi-Complementary (NO PNP output transistors) and clips assymmetrically when over driven. Individual transistors in some instances are soldered to each other's leads, rather than being individually mounted on the circuit boards.
Incredibly, the thermal contact between the output transistor heat sink and the bias transistor is through pieces of DUCT TAPE wrapped around the bias transistor collector tab resting against the heat sink! Offset adjustment is ridiculously sensitive. I have never seen or worked on such a shoddy design as the RGR model 5 in my entire 59 year career as an electronics technician.
In spite of these major shortcomings, this is a very good sounding amplifier. Keeping it operational, however, can be a major hassle. Mine has failed 4 times.
The matching preamplifier is built to a higher standard of quality than the amplifier, but is an unimpressive performer sonically.