Blue Circle BC3 Owners Manual?

Hello All

Does anyone know where I can locate the BC3 owners manual? Have searched high and low. Need to have a better understanding of the left and right TAPE toggle switches on the face of the unit. Has been ions since I have recorded music to a cassette or reel to reel , but is there a concern of damaging the preamp if the switches are simply utilized to mute music ?. - for example, if someone enters the room or the telephone rings, etc.. 

Thanks