According to Aracom, the Custom 45R provides the famous Marshall JTM45 tone with a few key features addeding versatility to the classic amplifier.
“Perfectly complimenting the JTM 45's tone is the built in tube driven spring reverb effect. The CUSTOM 45R is both a 40 watt and 20 watt amplifier by means of the Hi/Low B+ voltage switch. The PPI-Master Volume control, allows further control of the distortion and overall volume level.”
“Additional tone adjustments includes; the “Bright” switch on one channel and a “Bite” switch, that adds a bit more mid-gain to both channels. The CUSTOM 45R is available in both head and combo versions.”
More info at http://www.aracom-amps.com/products/45r.html