7844: Difference between revisions

Revision as of 09:22, 19 March 2015

{{{manufacturer}}}
400 MHz dual-beam non-storage mainframe Produced from 1975 to 1988 Manuals 7844/R7844 Operator's Manual (Rev. 11/1981, PDF, 3 MB) Tek 7844 Service Manual at BAMA (Rev. 02/1982, PDF, 109 MB) (All manuals in PDF format unless noted otherwise)

Manuals – Specifications – Links – Pictures

The Tektronix 7844 is a 400 MHz dual-beam CRT oscilloscope that takes two 7000-series vertical plug-ins and two 7000-series horizontal plug-ins.

Versions include the 7844 bench-top lab scope and R7844 rack-mount model.

A typical configuration might have included 7A19 or 7A24 amplifiers, 7B80/7B85 or 7B92A timebases.

Key Specifications

Bandwidth	400 MHz with 7A19, 7A29 (eq. 0.9 ns rise time), 300 MHz with 7A24
Fastest calibrated sweep	1 ns (with 7B80, 7B85, 7B92A)
Beam isolation	> 100:1 from DC to 150 MHz, > 30:1 from 150 MHz to 400 MHz
X-Y Phase Shift	< 2° from DC to min. 50 kHz
Horizontal bandwidth	DC to at least 1 MHz
Z axis input	2 V_p-p for full intensity range (positive decreases), input impedance 500 Ω, rise time 15 ns, max. 1 MHz
CRT	P-31 or P-11 (Opt. 78) phosphor, acceleration 24 kV (-3/+21)
Calibrator	4 mV, 40 mV, 400 mV or 4 V into >100 kΩ, 0.4 mV, 4 mV, 40 mV or 400 mV into 50 Ω; 1 kHz
Power	90-132 V or 180-264 V, 48 to 440 Hz, max. 235 W
Weight	16.3 kg (36 lbs) / R7844: 15 kg (33 lbs)

Internals

The 7844's CRT has distributed vertical deflection plates. It uses a number of custom ICs, such as 155-0065-00 and 155-0059-00 in the vertical amplifiers, 155-0095-00 in the vertical interface, 155-0078-00 in the trigger selector, and 155-0022-00 in the horizontal interface. The horizontal and Z axis amplifiers are discrete.

The power supply is a resonant switch-mode inverter with linear post-regulation, similar to the one in the 7904. It sues the 155-0067-02 controller. Despite having an SMPS, the 7844 is fairly heavy, which is mostly due to the second vertical delay line. The delay lines need extra space and are located vertically to the right of the CRT instead of below the CRT as in other 7xx4s.

Unlike some other 7000 series mainframes with switch mode PSUs, the 7844 does have a fan.

The 7844 is more complex than all other 7000 mainframes because vertical and horizontal amplifiers as well as the Z axis control boards exist twice, and there is an extra switching logic board. As a consequence, verifying correct operation requires testing many possible combinations of settings – for example, a defect on the vertical switching board could cause a problem only in the case of both beam 1 and 2 using horizontal bay B, but not if beam 1 used A and beam 2 used B. Moreover, calibration and adjustment is significantly more work than in a single-beam scope, e.g. CRT geometry trimpots need to be adjusted for matching both beams, not only for best geometry, and these adjustments slightly interact.

Links

Tek 7844 page at amplifier.cd and a repair report (switch-mode PSU)
Tek 7844 @ barrytech.com
R7844 page with frequency response measurements
Tek R7844 page @ EB5AGV, lots of internal photos

Prices

	Year	1976	1980	1984	1990 (7844R)
Mainframe only	Catalog price	$6,100	$9,125	$13,435	$19,500
Mainframe only	2014 value	$25,320	$26,150	$30,540	$35,230
Mainframe with 2 × 7A19, 7B85, 7B80	Catalog price	$9,500	$14,275	$21,520	$30,660
Mainframe with 2 × 7A19, 7B85, 7B80	2014 value	$39,430	$40,910	$48,910	$55,400

Pictures

Tektronix 7844 front view
Tektronix 7844 rear view
Simultaneous time and frequency domain display using a 7A26 amplifier, 7B92A time base, and 7L5 Spectrum Analyzer
Tektronix 7844 front view (with 7A26, 7A19(?), 7B80 and 7B85)
Tektronix R7844
7844 with options 78 (blue P11 phosphor) and 21 (dedicated vertical slots, i.e. no vertical mode switch)

Interior

Right interior. Top row: Calibrator board (l), readout board (c), beam 2 horizontal amplifier (r), fan.
Right/above interior. The dual delay lines can be seen behind the readout board. Horizontally mounted boards in the center are: Crossover mode switch (l), trigger selector (c), power supply (r).
Beam 2 vertical amplifier, CRT and termination detail (right side)
Left interior. Beam 1 vertical amplifier (l), crossover vertical interface (r).
Left/above interior. Top row: Beam 1 Z axis (l), Beam 1 / Beam 2 horizontal amplifiers (c/r).
Vertical mode switch board, back side
Vertical mode switch board, back side (detail)

@@ Line 8: / Line 8: @@
 MHz dual-beam non-storage mainframe|
 manuals=
-* [http://bama.edebris.com/manuals/tek/7844/ Tek 7844 Service Manual] at BAMA
+* [http://exodus.poly.edu/~kurt/manuals/manuals/Tektronix/TEK%207844%20R7844%20Instruction.pdf 7844/R7844 Operator's Manual] (Rev. 11/1981, PDF, 3 MB)
+* [http://bama.edebris.com/manuals/tek/7844/ Tek 7844 Service Manual] at BAMA (Rev. 02/1982, PDF, 109 MB)
 }}
 The '''Tektronix 7844''' is a 400 MHz [[dual-beam scopes|dual-beam CRT oscilloscope]]
@@ Line 15: / Line 16: @@
 Versions include the 7844 bench-top lab scope and R7844 rack-mount model.
-A typical configuration might have included [[7A24]] or [[7A19]] amplifiers, a [[7B80]] and a [[7B85]] timebase.
+A typical configuration might have included [[7A19]] or [[7A24]] amplifiers, [[7B80]]/[[7B85]] or [[7B92A]] timebases.
 {{BeginSpecs}}
-{{Spec | Bandwidth | 400 MHz (with [[7A19]], [[7A29]]) eq. 0.9 ns rise time }}
+{{Spec | Bandwidth | 400 MHz with [[7A19]], [[7A29]] (eq. 0.9 ns rise time), 300 MHz with [[7A24]] }}
-{{Spec | Fastest calibrated sweep | 1 ns (with [[7B80]], [[7B85]]) }}
+{{Spec | Fastest calibrated sweep | 1 ns (with [[7B80]], [[7B85]], [[7B92A]]) }}
+{{Spec | Beam isolation | > 100:1 from DC to 150 MHz, > 30:1 from 150 MHz to 400 MHz }}
+{{Spec | X-Y Phase Shift | < 2° from DC to min. 50 kHz }}
+{{Spec | Horizontal bandwidth | DC to at least 1 MHz }}
+{{Spec | Z axis input | 2 V<sub>p-p</sub> for full intensity range (positive decreases), input impedance 500 Ω, rise time 15  ns, max. 1 MHz }}
+{{Spec | CRT | P-31 or P-11 (Opt. 78) phosphor, acceleration 24 kV (-3/+21) }}
+{{Spec | Calibrator | 4 mV, 40 mV, 400 mV or 4 V into >100 kΩ, 0.4 mV, 4 mV, 40 mV or 400 mV into 50 Ω; 1 kHz }}
 {{Spec | Power | 90-132 V or 180-264 V, 48 to 440 Hz, max. 235 W }}
 {{Spec | Weight | 16.3 kg (36 lbs) / R7844: 15 kg (33 lbs)}}
@@ Line 25: / Line 32: @@
 ==Internals==
-The 7844's CRT has [[distributed vertical deflection plates]].
+The 7844's CRT has [[distributed vertical deflection plates]].  It uses a number of custom ICs, such as [[155-0065-00]] and [[155-0059-00]] in the vertical amplifiers, [[155-0095-00]] in the vertical interface, [[155-0078-00]] in the  trigger selector, and [[155-0022-00]] in the horizontal interface. The horizontal and Z axis amplifiers are discrete.
-The power supply is a resonant switch-mode inverter with linear post-regulation, similar to the one in the [[7904]].  Despite this, the 7844 is fairly heavy, which is mostly due to the second vertical delay line.  The delay lines need extra space and are located vertically to the right of the CRT instead of below the CRT as in other 7xx4s.
+The power supply is a resonant switch-mode inverter with linear post-regulation, similar to the one in the [[7904]].  It sues the [[155-0067-02]] controller.  Despite having an SMPS, the 7844 is fairly heavy, which is mostly due to the second vertical delay line.  The delay lines need extra space and are located vertically to the right of the CRT instead of below the CRT as in other 7xx4s.
-Unlike other 7000 series mainframes with switch mode PSUs, the 7844 does have a fan.
+Unlike some other 7000 series mainframes with switch mode PSUs, the 7844 does have a fan.
-The 7844 is more complex than all other 7000 mainframes because vertical and horizontal amplifiers as well as the Z axis control boards exist twice, and there is an extra switching logic board.
+The 7844 is more complex than all other 7000 mainframes because vertical and horizontal amplifiers as well as the Z axis control boards exist twice, and there is an extra switching logic board.  As a consequence, verifying correct operation requires testing many possible combinations of settings – for example, a defect on the vertical switching board could cause a problem only in the case of both beam 1 and 2 using horizontal bay B, but not if beam 1 used A and beam 2 used B.
+Moreover, calibration and adjustment is significantly more work than in a single-beam scope, e.g. CRT geometry trimpots need to be adjusted for matching both beams, not only for best geometry, and these adjustments slightly interact.
 ==Links==