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Tektronix 1L20
4.2 GHz Spectrum Analyzer plug-in
1L20 front

Compatible with 500-series scopes

Produced from 1965 to 1975

Manuals – Specifications – Links – Pictures

The Tektronix 1L20 is a spectrum analyzer plug-in for 500-series scopes. It covers the frequency range from 10 MHz to 4.2 GHz.

The 1L20 was originally the third-party Pentrix L-20. The model number was changed some time after Tektronix took over Pentrix in 1964.

Key Specifications

Frequency range 10 MHz to 4 GHz
Sensitivity −110 to −90 dBm
Dispersion 15 kHz to 60 MHz, magnifier usable to 2.5 kHz
Resolution bandwidth 1 kHz to 100 kHz, variable
Display log, lin, square, video


$1,995 in 1965 ($19,400 in 2023 dollars)


Originally (in SN 100-519), the UHF oscillator tubes V40 and V41 were type Y1506 (Tek part #154-0499-00). As the Y1506's became unavailable, a 1967 revision of the 1L20 changed these to Y1641 (GE 16411?) tubes (154-0506-00), necessitating a slight modification of their DC filament supply circuit.



Some Parts Used in the 1L20

Part Part Number(s) Class Description Used in
12AU6 154-0040-00 Vacuum Tube (Pentode) RF pentode 81 112 1L10 1L20 1L60 3L10 512 556 575 545 547 549 581 585 A B C G K H L ML M N O R S Z
Y1506 154-0499-00 Vacuum Tube (Triode) SHF cermet triode 1L20
Y1641 154-0506-00 154-0510-00 Vacuum Tube (Triode) SHF cermet triode 1L20 491