3L5

The Tektronix 3L5 is a 50 Hz − 1 MHz spectrum analyzer plug-in for 560-series scopes. It is very similar to the 1L5.

Tektronix 3L5
50 Hz - 1 MHz Spectrum Analyzer Plug-In Tektronix 3L5 Spectrum Analyzer Compatible with 560-series scopes Produced from 1967 to (?) manuals= Tektronix 3L5 Manual Tektronix 3L5 Factory Calibration Procedure, August 1967 Manuals {{{manuals}}} (All manuals in PDF format unless noted otherwise)

Manuals – Specifications – Links – Pictures

In conjunction with the 015-0107-00 Swept Frequency Converter (tracking generator), the 3L5 can also be used to make scalar frequency response measurements.

Key Specifications

Center Frequency	50 Hz to 990 kHz
Dispersion	10 Hz to 100 kHz
Input Impedance	1 MΩ // 30 pF
Input Voltage	Max. 300 V (DC + peak AC)
Vertical Resolution	Video: 100 mV/div to 100 V/div, LIN: 1 mV to 2 V_RMS
Internal Cal Signal	5 kHz ±1%
First LO Out	≥1 MHz (Sweep), ≥1 V_p-p into ≥1 kΩ
Recorder Out	5 mV to 15 mV into 600 Ω
Weight	2.7 kg / 6 lbs

A video filter switch was added to the later SNs (1971 Catalog).

Internals

The 3L5 is a full semiconductor design except for the final output amplifier, which uses a 8416 vacuum tube. The circuit is based on the swept-frontend design, i.e. the first local oscillator is swept for the spectrum scan.

75 Ω Version

There is also a 75 Ω version of the 3L5. Its input is on the rear, via a coaxial connector. A lever on the front panel switches between two frequency ranges:

10 kHz − 1 MHz
18.010 MHz − 19 MHz

Timebase Support

The 3L5 requires a timebase plug-in in the horizontal compartment to operate.

Timebase plug-in units with serial numbers listed below require modification 040-0413-00 to provide the sweep signal to the 3L5 (To pin 18 of the plug-in connector).

Time Base	SN#
2B67	<15180
3B1	<4040
3B3	<4270
3B4	<740

Pictures

1 MΩ version

Front
Left
Right
1 MΩ Version
1 MΩ Later Version with Video Filter Switch
LHS
RHS
Top
Bottom
Internals - 3 MHz Filter, 2nd LO (3.1 MHz) and 2nd Mixer.
Internals - 3 MHz Filter, 2nd LO (3.1 MHz) and 2nd Mixer.
Internals - 100 kHz Crystal from Variable Resolution Amp 158-0022-00
Internals - 100 kHz crystal from Variable Resolution Amp 158-0022-00

75 Ω version

75 Ω Version of 3L5, Front
75 Ω Version, Front/Top
75 Ω Version, Left
75 Ω Version, Top
75 Ω Version, Bottom/Left
75 Ω Version
75 Ω Version
75 Ω Version, Back

Components

Some Parts Used in the 3L5

Part	Part Number(s)	Class	Description	Used in
1N3182	152-0269-00	Discrete component	varactor diode	3L5 • 1L5 • 3T7 • 492 • 465M • 7844 • 2465
8416	154-0413-00 • 157-0116-00	Vacuum Tube (Dual Triode)	dual triode	1S1 • 2A61 • 3A8 • 3L5 • W