The EC97 was designed for use as an RF amplifier in VHF television tuners. This valve has a 6.3 Volt heater for parallel supply and this valve was most likely used in applications where a fully isolated chassis was employed and a mains transformer was fitted. For domestic equipment the 300 mA series heater version the PC97 was more appropriate.
The anode from the side.
The anode face view.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 47 mm tall.
References: Data-sheet & 1040. Type EC97 was first introduced in 1962.