[R-390] More Ballast Thoughts in re 6T4F and 3TF7

[Norman Ryan]

Hi, Glen and gang,

Just looked in an old (1969, 33rd edition) Radio-Electronic Master
catalog and came away with the following.

Amperite numbering system in general (not consistent!):
First digit-- threshold current in tenths of an ampere.
Letters-- envelope type.
Last digit-- threshold voltage in volts.
Last letter-- not sure; version perhaps?

Thus 3TF7 = .3 ampere threshold current, T6-1/2 bulb 9 pin miniature, 7
volts threshold voltage.

6T4F = .6 ampere threshold current, T5-1/2 7 pin minature, 4 volts
threshold voltage. 

List price for all these ballast tubes back then?  One price: $1.80.