The Tektronix 561 is a general-purpose oscilloscope mainframe introduced in 1961, featuring a modular plug-in architecture that bridges tube-era and semiconductor instrumentation. The instrument accepts two plug-in units—one for vertical amplification (left-hand opening) and one for horizontal amplification (right-hand opening)—enabling users to customize measurement capabilities for specific applications. A 3-inch rectangular CRT with P31 phosphor and variable edge-lighted internal graticule provides an 8 by 10 division viewing area with 5 minor divisions marked on each major division centerline.
Technical Specifications
• Display: 3-inch CRT, Type T561 ceramic envelope, P31 phosphor
• Graticule: 8 vertical by 10 horizontal divisions; 5 minor divisions per major division (centerline)
• Usable Viewing Area: 8 divisions (vertical) × 10 divisions (horizontal)
• Accelerating Potential: Approximately 3.5 kV
• Deflection Plate Sensitivities: Vertical 18.5–20.5 V/division; Horizontal 17.5–19.3 V/division
• Bandwidth: 10 MHz (general-purpose configuration); determined by installed plug-in units
• Calibrator: Square-wave output, 0.2 mV to 100 V peak-to-peak in 18 steps; ±3% accuracy; 4 µs typical risetime; line-frequency synchronized
• Warm-up Time: 15–20 minutes to stabilization
• Operating Temperature: Up to 50° C with thermal cutout protection
– Key Features
• Modular plug-in design for vertical and horizontal channel customization
• Electronically regulated power supplies maintain stable operation across varying line voltages and loads
• Line voltage selectable: 105–125 VAC or 210–250 VAC, ±10%, 50–60 Hz (up to 400 Hz in some configurations)
• Low-voltage regulated outputs: +100 V, +12.2 V, +125 V, +300 V; unregulated +420 V
• Dual negative high-voltage supplies for CRT bias and control grid
• No-parallax internal graticule with variable edge lighting
– Compatibility & Integration
Accepts Tektronix ‘2’ Series or ‘3’ Series plug-in units for both vertical and horizontal functions. Early plug-in designs with specific guide configurations may have physical compatibility limitations with certain 560 series mainframes.
