Series 4

The "Ferrograph" is a versatile magnetic tape recorder. It is a machine of high quality, yet simple to operate. In its time, it was marketed as useful to both those who are technically unskilled as well as to engineers or those who use tape recorders professionally. The tape it uses is 1/4" wide. Model 4A has two tape speeds, 3 3/4 and 7 1/2 ips, while Model 4AH has speeds of 7 1/2 and 15 ips. It features components including an amplifier for magnifying weak microphone signals, a recording head for the conversion of electrical energy into magnetic energy to impress upon the tape, and a playback head for picking up the magnetic impressions made on the tape and converting them back into electrical energy.

Series 6 

The Ferrograph was semi professional machine seen many times in films and used by the BBC. This version of the Series 6 is a half track stereo machine with 8.25 inch reels and using standard 1/4 inch tape. A quarter track version was available. It had three motors, two used for fast forward, rewind and back tension and one, a split phase capacitor induction motor, for the flywheel and capstan. This type of motor is almost immune to small variations in voltage or load and is controlled by the mains frequency after reaching its synchronous speed. Three speeds were provided 7.5, 3.75, and 1.125 inches/second. It was extremely heavy using valve amplification and built on a sturdy frame.