They were used in cable-TV 'launch amplifiers' - the circuit of the type designed by EMI and used in the Abingdon cable-TV project is here:
http://www.aeolian-hall.myzen.co.uk/circuit.gif
http://www.aeolian-hall.myzen.co.uk/fig28a.gif
[Complete description of Abingdon cable-TV is here:
http://www.aeolian-hall.myzen.co.uk/mva.htm ]