The EM87 indicator uses the closing bar principle and is housed in a standard miniature valve envelope. Mullard describe the EM87 as a voltage level indicator for use in tape recorders.
The EM87 has the same base connections as the EM85E and differs in sensitivity, anode voltage and anode current. The manufacturers short form catalogue lists both as tuning indicators and gives no guide as to differences. The base connections are also the same for the popular EM84, although this has a much greater voltage range.
This example was made in Western Germany.
The triode voltage amplifier is on the left with the green display on the right.
The phosphor strip is deposited on the inside of the envelope.
The cathode is triangular with the rounded point being oxide coated.
Microscope image of the back of the cathode. The control grid can be seen extending beyond the anode wall.
Close-up of the cathode tube showing the coiled insulated heater.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 64 mm tall.
References: Data-sheet & 1040. Type EM87 was first introduced in 1961. See also1961 adverts.
