The Mullard tuning indicator EM87
The EM87 is a new Mullard voltage indicator tube primarily intended for use as a recording level indicator in tape recorders.
In many recorders the AF voltage appearing at the anode of the recording output stage is about 10V. which is insufficient to close the display of currently available level indicators. The EM87 has a grid base of only 10V and in addition it has a high sensitivity in the initial region of the control characteristic (Vg=0V).
Over-modulation of the tape is immediately apparent. since AF signals greater than 10V in amplitude cause the luminous areas to overlap, giving a brighter centre portion to the display.
Maximum ratings are: anode voltage 300 V, anode dissipation 600 mW, cathode current 5 mA, and deflection electrode voltage 300 V. The heater draws a current of 300 mA at 6.3 V.
The EM87 has the same overall physical dimensions (72.8mm overall length x 22.2mm diameter) and the same pin connections as the EM84. The fluorescent strip is 32.6mm in length by 4mm in width.