The Tektronix Type L is an amplifier plug-in for 500-series scopes.
The Type L is a Type K plus a 10x-gain AC-coupled preamp
that extends the maximum sensitivity to 5 mV/div.
Bandwidth in a 545 is 30 MHz at 50 mV/div and above, 3 Hz-24 MHz at 20 mV/div and below.
Type 53/54L was introduced in 1957 along with the 536 and its companion
53/54T sweep plug-in. It was renamed the Type L in 1959.
It was the fastest 5 mV plug-in until the 1A1 in 1964.
It was dropped after 1972.
K, L, and T are tied for longest production life, at 16 years.
B, D, and G are next at 15 years.
Late versions have a BNC connector instead of a UHF connector.
Lavoie Laboratories produced an unauthorized clone, the LA-265-L.
Performance in Different Scopes