T7100

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The Tektronix T7100 (P/N 154-0783-00 with P31 phosphor) is the CRT used in the 7104 and R7103 analog 1 GHz scopes. It features a micro-channel plate electron beam amplification stage.

MCP diagram
(click image to enlarge)

Compared to non-MCP high-speed tubes, the T7100 uses reduced beam current and acceleration voltage to achieve high deflection sensitivity, eliminating the need for high amplifier output voltages, thereby boosting amplifier bandwidth.

The electron beam passes through terminated helical deflection plates (both X and Y axes use this form of distributed deflection plates to achieve the necessary bandwidth), followed by an electrostatic scan-expansion lens that increases deflection 4.5 times vertically and 4 times horizontally, before it hits the micro-channel plate (MCP). The deflection structures are described in US Patent 4,093,891. The scan-expansion lens is a "box lens" design, which is discussed on pages 53−55 of the 7104 maintenance document.

The MCP consists of parallel channels of 25 μm diameter and offset at a slight angle to the beam. The inside walls of these channels are coated with resistive material, with a voltage of 700-1050 V applied between back and front of the plate. Electrons entering a channel hit the wall where they initiate a cascade of secondary electron emission like in a photomultiplier.

A final 10 kV potential accelerates the beam across a 3 mm gap toward the phosphor coating.

The beam amplification is sufficient to view a single-shot event at 200 ps/Div with the naked eye.

The Micro-channel plate's amplification degrades irreversibly with operation, in proportion to the log of total charge passed per channel or display area. For this reason, continued operation with a steady trace and especially at large beam currents must be avoided. The 7104 contains a CRT protection circuit that shuts off the beam after a time depending on the beam current.

Specifications

Screen size 8 × 10 Div. @ 8.5 mm
Resolution 17 lines / Div.
Vertical deflection factor 1 V/cm
Vertical deflection impedance 200  Ω
Vertical bandwidth 2.6 GHz (3 GHz spec claimed in maintenance document linked below)
Horizontal deflection factor 2 V/Div
Horizontal deflection impedance 365 Ω
Horizontal bandwidth 1.5 GHz

Links

Pictures

Screen shots