The following Brown Bros key page contains all existing models.
UTL unbased twin lever-1964
Used on BTL but offered separately.
UTL-A unbased twin lever-1974
Used on the BTL-A, and offered separately. The base shown here is not part of the key.
ST Straight Key-1964
First straight key model sold in 1964.
ST-A Straight Key-1974
1974 improved straight key.
BTL based twin lever-1964
First available twin lever paddle in 1964.
BTL-A based twin lever-1974
Improved twin lever 1974 model.
BTL with magnetic paddle –year unknown
(Photo courtesy-Jan Skoldin,SM5LNE)
Only 5~6 made, two known. John at morsemad calls it the MTL model.
CTL combination twin lever-1964
Combination key with twin lever paddle and ST Straight key.
CTL-A combination twin lever-1974
Combination Key with Improved BTL-A paddle & ST Straight key.
CTL-B combination key-1976
Combination key with BTL-A & ST-A Straight key
CSA combination key-1964
Scare unit, probably only 12 units made.
ES [single lever paddle] {year unknown}
Only a couple of dozen made. Ext. rare.
CTL-B with built-in electronic keyer [year unknown]
Rare, only 2~3 known in existence. (Photo courtesy: Ed, N3CW)