In line with many other guitar amplifier manufacturers, the Bird company made a move towards solid state in 1965 with these two 50watt amplifier/speaker combinations, the L/50 for lead and rhythm guitars, and the B/50 for bass and rhythm guitars.
The L/50 was provided with a speaker cabinet housing 2 x 12" units and the B/50 cabinet was pressurized and used a single 18" speaker. Both amp heads were twin channel, with the L/50 being provided with tremolo and treble boost on one of its channels.
Presumably, these two amps were marketed in parallel with the equivalent output Bird valve amps, an example of which is shown HERE. The production run of the L/50 and B/50 is not known, but it can not have been very long as the single advertisement shown below is the only record that we have come across of these rare beasts.
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The L/50 & B/50 scanned from a Bird advertisement of February 1965.