Arthur Radford, started Radford Electronics in 1946 and from the outset built up a reputation of designing high quality valve amplifiers with extremely low distortion figures. So low was the distortion that they had to build their own custom test equipment sensitive enough to measure it! In 1961, they released the STA range of amplifiers featuring a new transformer design that reduced distortion by a factor of 10 from previous amps, placing it as one of the best amps on the market at the time.
Today, these amplifiers are highly prized, don’t appear on the market very often and when they do, demand high prices. More so the STA power amplifiers than the SC22 pre-amplifier, but ideally the pair should be kept together. Expect this STA25 to sell for around £1000, the SC22 around £250-300.