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The Tektronix 7J20, which only appears in the 1975 catalog, is a "rapid scan" optical spectrometer for the 250 nm to 1100 nm region. Rapid scan means that it can capture the spectrum quickly enough to show spectral changes at temporal resolution of a few milliseconds. The spectrometer is packaged in two enclosures linked by an umbilical cable. The 7J20 is a 2-wide plug-in for 7000-series scopes containing the sweep timing and mainframe interface circuits. The external enclosure is labeled "J20". It has controls for the optical components (grating, filters etc.) on one side and an input aperture on the other.


The instrument is based on a Czerny-Turner Monochromator, in essence a narrow slit followed by a diffraction grating. A vidicon tube scans the optical spectrum and produces a periodic electric signal which is then displayed by the scope mainframe.

Operating principle (click to enlarge)

The internal vidicon horizontal scan voltage corresponds to wavelength, but not in a linear way. To provide a linear nm/div horizontal display on the 7000-series mainframe, the vidicon horizontal scan signal is passed through a function generator IC, the 155-0106-00 (U1550 and U1590), which implements an interpolated lookup table. Inside the J20, there are 40 trimmer potentiometers that allow the lookup function to be tweaked so that the horizontal scale of the system is accurate.

Normalizer (click to enlarge)

The 7J20 is very rare. According to Dennis Tillman, Best estimate is ~40 were actually built.


Spectral range 250 nm to 1100 nm
Resolution (Grating A) ≤4 nm in a 400 nm span (selectable 300-700, 400-800, 500-900, 600-1000, or 700-1100 nm
Resolution (Grating B) ≤0.4 nm in a 40 nm span continuously variable through the spectral range
Slit 10 to 5000 μm wide (1-2-5 sequence), 10 mm high
Filters ND1, ND 2, 500 nm monopass, 800 nm monopass, UV block (≤400 nm), UV pass (250-330 nm), open (no filter)
Scan 10 or 20 ms base sweep, 50 to 1000 ms (1-2-5) settings run successive 20 ms sweeps up to the selected integration time
Display span Grating A, 40, 20, 10 or 4 nm/Div ; Grating B, 4, 2, 1 or 0.4 nm/Div


$12,000 in 1975 (~$61,000 in 2021 dollars)



Custom ICs used in the 7J20

Page Class Manufacturer Model Part nos Description Designers Used in
155-0014-01 Monolithic integrated circuit Tektronix M019D 155-0014-01 A/D converter Barrie Gilbert 7000 series readout system 5403 5440 5441 5443 5444 7313 7504 7514 7603 7613 7623 7633 7704 7704A 7844 7904 R7903 7904A 7912 7J20 P7001
155-0090-00 Monolithic integrated circuit Tektronix M059 155-0090-00 155-0090-01 155-0090-02 four-decade counter Mike Metcalf 7D01 7D12 7D15 7B85 7J20
155-0104-00 Monolithic integrated circuit Tektronix M169 155-0104-00 custom legend generator Mike Metcalf Roger McCoy 7J20
155-0105-00 Monolithic integrated circuit Tektronix M170 155-0105-00 custom legend generator Mike Metcalf Roger McCoy 7J20
155-0171-00 Monolithic integrated circuit Tektronix M150A 155-0171-00 4-decade counter, latch and D/A converter Mike Metcalf 7B85 7D01 7D12 7D15 7J20
M092 Monolithic integrated circuit Tektronix M092 155-0086-00 155-0087-00 155-0088-00 155-0104-00 155-0105-00 legend generator Roger McCoy Mike Metcalf 7D15 7J20

Custom ICs used in the J20

Page Class Manufacturer Model Part nos Description Designers Used in
155-0106-00 Monolithic integrated circuit Tektronix M101 155-0106-00 normalizer J20