The EF89 is a miniature RF voltage amplifier. Mullard describe the EF89 as a variable μ pentode for use as an RF or IF amplifier in FM/AM receivers and is designed to work with a tuned anode circuit.
This exhibit was labelled on the wrapper as a Mullard 5885. Looking for data on the 5885 revealed that it was made with flying leads - not the valve here at all. Looking at the lettering revealed that the only positive identification was the 5 at position three.
The next step was to look at the pins and determine the pin-out. Armed with the fact that it was a B9A base and known pin connections the museum advance search was used. Firstly with the B9A base and screen at position 1. With a list being returned the search was refined by adding the position of the second screen connection. This returned nine entries as below.
The heater was powered-up and at 6.3 volts took 0.21 Amps. The EF89 was the match.
Knowing the most probable answer the Type on the envelope was read again. The first character certainly looks like an E with three bars to the right of the vertical stroke. The second character has one middle horizontal bar visible. The final character has the curves of a nine.
Unlike other EF89s we have seen this one has a solid screen rather than a perforated one.
The lower mica is made of two sheets - the requirement for vibration resistance.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 53 mm tall.
References: Data-sheet & 1040. Type EF89 was first introduced in 1954. See also1954 adverts.
