We have serviced all of the Radford preamps, from the valve SC22 to the solid-state SC24 and ZD-22, the latter being also built into the HD and ZD power amplifier series. They are all remarkable, especially the SC22, which however does exhibit a not quite flat frequency response 20-20kHz (±0.3dB) due to the tone control section design, and not startlingly accurate RIAA phono equalization.
The umbilical cable used between the SC22 and the MA- and STA- power amplifiers is wired as shown in the table below. It is wired 1-1, 2-2, 3-3, 4-4, 5-5, 6-6, 7-7, 8-8. Please note that this is NOT COMPATIBLE with the majority of Leak umbilical cables.
|SC22||Heater||E via R42 56R||AC||AC||AC=3, switched||HT||Heater|
|SC22P||No socket: this unit is self-powered.|
|MA series||Heater||E||AC=4||AC||AC||AC=4, switched||HT||Heater|
|STA series||Heater||E||AC=4||AC||AC||AC=4, switched||HT||Heater|
|Source: published Radford schematics. No responsibility is taken for any errors or omissions.|