Difference between revisions of "7904"

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manuals=
 
manuals=
 
* [http://bama.edebris.com/download/tek/7904/Tektronix_7904_Service_May1983.pdf Tektronix 7904 Manual (PDF)]
 
* [http://bama.edebris.com/download/tek/7904/Tektronix_7904_Service_May1983.pdf Tektronix 7904 Manual (PDF)]
* [http://www.ko4bb.com/Manuals/Tektronix/Tektronix_-_7904A/7904a-service-1990.djvu Tektronix 7904A Manual (DjVu)]
+
* [http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Tektronix/Tektronix_-_7904A Tektronix 7904A Manual (DjVu)]
 
* [http://w140.com/Tektronix_7904A_OCRed_by_Tabalabs.pdf Tektronix 7904A Manual (Shannon Hill PDF with OCR)]
 
* [http://w140.com/Tektronix_7904A_OCRed_by_Tabalabs.pdf Tektronix 7904A Manual (Shannon Hill PDF with OCR)]
 
* [http://w140.com/Tek_7904_OCRed_by_Tabalabs.pdf Tektronix 7904 Manual (Shannon Hill PDF with OCR)]
 
* [http://w140.com/Tek_7904_OCRed_by_Tabalabs.pdf Tektronix 7904 Manual (Shannon Hill PDF with OCR)]
 
* [http://w140.com/Tek_7904_Power_Supply.pdf Servicing the 7904 High-Efficiency Power Supply (PDF)]
 
* [http://w140.com/Tek_7904_Power_Supply.pdf Servicing the 7904 High-Efficiency Power Supply (PDF)]
 +
<small>
 +
'''Modifications'''
 +
* [http://hakanh.com/dl/docs/kitinstructions/050-0650-00.pdf 050-0650-00 (1980) Vertical amplifier IC replacement]
 +
* [http://hakanh.com/dl/docs/kitinstructions/050-0651-01.pdf 050-0651-01 (1975) Vertical output IC replacement (155-0065-00)]
 +
* [http://hakanh.com/dl/docs/kitinstructions/050-0706-01.pdf 050-0706-01 (1980) Vertical output IC replacement (155-0065-00)]
 +
* [http://hakanh.com/dl/docs/kitinstructions/050-0729-06.pdf 050-0729-06 (1980) A Trigger selector circuit board replacement]
 +
* [http://hakanh.com/dl/docs/kitinstructions/050-0730-06.pdf 050-0730-06 (1980) B Trigger selector circuit board replacement]
 +
* [http://hakanh.com/dl/docs/kitinstructions/050-0763-03.pdf 050-0763-03 (1981) Vertical interface circuit board replacement]
 +
* [http://hakanh.com/dl/docs/kitinstructions/050-1014-00.pdf 050-1014-00 (1980) Vertical output IC replacement] ([[155-0064-00]])
 +
* [http://hakanh.com/dl/docs/kitinstructions/050-1723-01.pdf 050-1723-01 (1983) P31 CRT replacement]
 +
* [http://hakanh.com/dl/docs/custommods/7904mod721K.pdf Custom Mod 721K (1972) Single shot readout and/or grat illumination]
 +
</small>
 
}}
 
}}
The '''Tektronix 7904''' is a 500 MHz, non-storage 7000-series oscilloscope mainframe with four bays. It accepts two [[7000-series_plug-ins#Vertical plug-ins|7000-series vertical plug-ins]] and two [[7000-series_plug-ins#Horizontal plug-ins|7000-series horizontal plug-ins]]. It was introduced in late 1971/early 1972 (Note 1). The successor model 7904A was introduced in 1974. There is also a rack-mount version, the [[R7903]], albeit with only one horizontal bay.
+
The '''Tektronix 7904''' is a 500 MHz, non-storage 7000-series oscilloscope mainframe with four bays.
 +
It accepts two [[7000-series_plug-ins#Vertical plug-ins|7000-series vertical plug-ins]] and two [[7000-series_plug-ins#Horizontal plug-ins|7000-series horizontal plug-ins]].
 +
It was introduced in late 1971/early 1972 (Note 1).
 +
The successor model 7904A was introduced in 1984.
 +
There is also a rack-mount version, the [[R7903]], albeit with only one horizontal bay.
  
Performance is largely determined by the plug-ins. The [[7A19]] vertical amplifier and [[7B92]] time base were introduced along with the 7904 to match the 500 MHz system bandwidth.   
+
Performance is largely determined by the plug-ins.
 +
The [[7A19]] vertical amplifier and [[7B92]] time base were introduced along with the 7904 to match the 500 MHz system bandwidth.   
  
===7904A differences===
+
Design Staff of 7904 Project (from July 1971 Tekscope):
The 7904 had an elaborate 5-decade built-in calibrator with variable rate that was dropped from the 7904A.  In the 7904A, The Control Illumination switch moved to the rear panel, and the [[7000 series readout system|readout system]] gained a pulsed mode in which it is synchronized with the sweep instead of interrupting the display at random times.  This pulsed mode is not compatible with all time base plug-ins (see manual p. 1-12).
+
* [[Val Garuts]], project manager and horizontal and Z-axis amplifiers
 +
* [[Thor Hallen]], vertical amplifier and [[7A19]]
 +
* [[John McCormick]], horizontal amplifier
 +
* [[Les Larson]] and [[Bill DeVey]], trigger and timebase ([[7B92]])
 +
* [[Bill Peek]], Z-axis amplifier and autofocus
 +
* [[Hans Springer]], mainframe interface and channel switching
 +
* [[Joe Burger]], power supply
 +
* [[Joel Swanno]], mechanical design
 +
* [[Ken Hawken]], CRT
  
==Specifications==
 
 
{{BeginSpecs}}
 
{{BeginSpecs}}
 
{{Spec | Bandwidth | 500 MHz }}
 
{{Spec | Bandwidth | 500 MHz }}
 
{{Spec | Fastest calibrated sweep | 500 ps/Div (with [[7B92A]], other time bases "uncalibrated for first 60 ns") }}
 
{{Spec | Fastest calibrated sweep | 500 ps/Div (with [[7B92A]], other time bases "uncalibrated for first 60 ns") }}
{{Spec | Acceleration voltage | 24 kV }}
+
{{Spec | Acceleration voltage | 24 kV (+21 / -3 kV) }}
 
{{Spec | Calibrator (7904) | 4 mV, 40 mV, 400 mV, 4 V or 40 V (p-p) into 1 MΩ; 2 mV, 20 mV, 200 mV or 400 mV into 50 Ω; or 40 mA; selectable 1 kHz, ½ rep. rate of B Sweep Gate, or DC }}
 
{{Spec | Calibrator (7904) | 4 mV, 40 mV, 400 mV, 4 V or 40 V (p-p) into 1 MΩ; 2 mV, 20 mV, 200 mV or 400 mV into 50 Ω; or 40 mA; selectable 1 kHz, ½ rep. rate of B Sweep Gate, or DC }}
 
{{Spec | Calibrator (7904A) | 4 mV to 4 V (p-p) in decade steps, 1 kHz; 40 mV to 400 mV into 50 Ω }}
 
{{Spec | Calibrator (7904A) | 4 mV to 4 V (p-p) in decade steps, 1 kHz; 40 mV to 400 mV into 50 Ω }}
Line 34: Line 58:
 
}}
 
}}
 
{{EndSpecs}}
 
{{EndSpecs}}
 +
 +
===7904A differences===
 +
The 7904A re-implements the vertical amplifier using Hypcon-packaged amplifier chips designed for the [[7104]], such as the [[155-0178-00]].
 +
 +
The 7904 had an elaborate 5-decade built-in calibrator with variable rate that was dropped from the 7904A. The [[7904 remote control connector|rear remote control connector]] unique to the 7904 was dropped as well.
 +
In the 7904A, The Control Illumination switch moved to the rear panel, and the [[7000 series readout system|readout system]]
 +
gained a pulsed mode in which it is synchronized with the sweep instead of interrupting the display at random times.
 +
This pulsed mode is not compatible with all time base plug-ins (see manual p. 1-12).
 +
 +
===Options===
 +
<div style="column-count:4;-moz-column-count:4;-webkit-column-count:4">
 +
* Opt.2: X-Y delay compensation network
 +
* Opt.3: Extra EMI shielding
 +
* Opt.4: Maximum-brightness CRT with reduced area
 +
* Opt.78: P11 phosphor
 +
</div>
  
 
==Operation==
 
==Operation==
  
The 7904 has a many modes of operation. One mode is called "Independent-Pairs Display" in the manual, where the input to the left vertical plug-in is displayed using the B horizontal time-base plug-in, and the input to the right vertical plug-in is displayed using the A horizontal time-base plug-in. This resembles the trace-slaving "ALT" mode that is produced by an [[1A4]] in a [[547]]. Many other modes are available. It is possible to put vertical plug-ins in the horizontal slots for X-Y operation. It is even possible to put a horizontal plug-in in one of the vertical slots to produce a raster scan.   
+
The 7904 has many modes of operation.
 +
One mode is called "Independent-Pairs Display" in the manual, where the input to the left vertical plug-in is displayed using the B horizontal time-base plug-in,
 +
and the input to the right vertical plug-in is displayed using the A horizontal time-base plug-in.
 +
This resembles the trace-slaving "ALT" mode that is produced by an [[1A4]] in a [[547]].
 +
Many other modes are available.
 +
It is possible to put vertical plug-ins in the horizontal slots for X-Y operation.
 +
It is even possible to put a horizontal plug-in in one of the vertical slots to produce a raster scan.   
 +
 
 +
A special plug-in, the [[7A21N]], provides direct access to the deflection plates up to 1 GHz at an uncalibrated sensitivity of 4 V/Div.
 +
This plugin requires modifications to the mainframe to bypass the Y output amplifier (thus disabling readout and the other vertical plugin bay).
  
A special plug-in, the [[7A21N]], provides direct access to the deflection plates up to 1 GHz at an uncalibrated sensitivity of 4 V/Div.  This plugin requires modifications to the mainframe to bypass the Y output amplifier (thus disabling readout and the other vertical plugin bay).
+
A rear-panel [[7904 remote control connector| remote control connector]] has connections for single-sweep ready lamps, a reset button, and readout control.
  
 
==Internals==
 
==Internals==
The 7904 uses a switch-mode power supply and has no fan. It incorporates a 65 ns Y delay line. This delay is too short for some older time bases such as [[7B53]] to display the trigger event.
+
The 7904 uses a switch-mode power supply and has no fan. It incorporates a 65 ns Y delay line.
 +
This delay is too short for some older time bases such as [[7B53]] to display the trigger event.
 +
 
 +
[[Thor Hallen]] designed the main vertical amplifier and the [[7A19]] plugin (Note 1).
 +
It used bridged T coils and the "[[ft doubler|f<sub>t</sub> doubler]]" circuit patented by [[Carl Battjes]] to achieve its bandwidth.
  
The 7904 makes extensive use of custom integrated circuits and hybrid circuits, inter alia, the [[155-0064-00]] 470-ps output amplifier, [[155-0022-00]] analog multiplexer for channel switching, [[155-0059-00]] HF amplifier, [[155-0095-01]] and [[155-0095-03]] differential HF amplifiers, and [[155-0067-02]] SMPS controller.
+
The 7904 makes extensive use of custom integrated circuits and hybrid circuits, inter alia, the [[155-0064-00]] 470-ps output amplifier,
 +
[[155-0022-00]] analog multiplexer for channel switching, [[155-0059-00]] HF amplifier,
 +
[[155-0095-01]] and [[155-0095-03]] differential HF amplifiers, and [[155-0067-02]] SMPS controller.
  
 
The 7904A includes [[155-0173-05]], [[155-0175-05]] and [[155-0178-05]] amplifiers.
 
The 7904A includes [[155-0173-05]], [[155-0175-05]] and [[155-0178-05]] amplifiers.
  
The signal path is completely differential and all of the internal wiring is 50 Ω coax. The CRT ([[154-0644-05]]) has distributed vertical deflection plates.
+
The signal path is completely differential and the internal signal wiring is 50 Ω coax.
 +
The CRT ([[154-0644-05]]) has [[distributed vertical deflection plates]].
  
 
==Prices==
 
==Prices==
1990: $12,750 (7904A) = $23,200 @ 2014 value
+
{| class="wikitable"
 +
|-
 +
! &nbsp;
 +
! Year
 +
! 1972
 +
! 1976
 +
! 1980
 +
! 1984
 +
! 1990
 +
|-
 +
! Model
 +
|
 +
|align=center| 7904
 +
|align=center| 7904
 +
|align=center| 7904
 +
|align=center| 7904A
 +
|align=center| 7904A
 +
|-
 +
!rowspan=2| Mainframe only
 +
! Catalog price
 +
|align=right|  $2,900
 +
|align=right|  $4,100
 +
|align=right|  $6,265
 +
|align=right|  $8,810
 +
|align=right| $12,750
 +
|-
 +
! 2019 value
 +
|align=right| $17,640
 +
|align=right| $18,320
 +
|align=right| $19,330
 +
|align=right| $21,550
 +
|align=right| $24,800
 +
|-
 +
!rowspan=2| Mainframe with [[7A19]],<br />7A19 Opt. 04, [[7B92]]
 +
! Catalog price
 +
|align=right|  $5,500
 +
|align=right|  $7,765
 +
|align=right| $12,015
 +
|align=right| $17,425
 +
|align=right| $24,190
 +
|-
 +
! 2019 value
 +
|align=right| $33,450
 +
|align=right| $34,690
 +
|align=right| $37,070
 +
|align=right| $42,630
 +
|align=right| $47,050
 +
|}
  
 
==Links==
 
==Links==
  
* [http://amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/7904.htm Tek 7904 page at amplifier.cd]
+
* [https://lazyelectrons.wordpress.com/2018/11/24/tektronix-7904-oscilloscope-power-supply-repair/ 7904 Repair with Video]
* [http://amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/7904A.htm Tek 7904A page at amplifier.cd]
+
* [[Media:Tekscope 1971 V3 N4 Jul 1971.pdf | Tekscope Vol. 3 No. 4, Jul 1971]]
 +
* [http://amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/7904.htm Tek 7904] / [http://amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/7904A.htm 7904A] @ amplifier.cd
 +
* [http://www.barrytech.com/tektronix/tek7000/tek7904.html Tek 7904] / [http://www.barrytech.com/tektronix/tek7000/tek7904a.html 7904A] @ barrytech.com
 
* [https://www.circuitsathome.com/measurements/repairing-front-panel-buttons-of-tektronix-7904-oscilloscope Repairing front panel buttons of Tektronix 7904 oscilloscope]
 
* [https://www.circuitsathome.com/measurements/repairing-front-panel-buttons-of-tektronix-7904-oscilloscope Repairing front panel buttons of Tektronix 7904 oscilloscope]
* [http://www.ko4bb.com/Manuals/Tektronix/Tektronix_-_7904A/Tek_7904_Power_Supply.pdf Servicing the 7904 high-efficiency power supply (Tektronix ServiceScope article)]
 
  
 
==Notes==
 
==Notes==
# See [[7A11]] and [[John Addis]], ''Good Engineering and Fast Vertical Amplifiers'', in Jim Williams (Ed.), ''Analog Circuit Design: Art, Science and Personalities'' (1991), p.114, and [http://w140.com/tektronix_new_products_1972.pdf Tektronix New Products 1972] brochure.
+
# See [[7A11]] and [[John Addis]], ''Good Engineering and Fast Vertical Amplifiers'', in [[Jim Williams]] (Ed.), ''Analog Circuit Design: Art, Science and Personalities'' (1991), p.114, and [http://w140.com/tektronix_new_products_1972.pdf Tektronix New Products 1972] brochure.
 
   
 
   
 
==Pictures==
 
==Pictures==
Line 67: Line 171:
 
===7904 non-A===
 
===7904 non-A===
 
<gallery>
 
<gallery>
File:Tek-7904-front.jpg | 7904  (non-A) front
+
Tek-7904-front.jpg | 7904  (non-A) front
File:7904-left.jpg | Left side. Left top: Vertical amplifier; left bottom: switch-mode power supply; right center: delay line; right bottom: plug-in bays
+
Tek 7904 rear.jpg | 7904 rear
File:7904-right.jpg | Right side.  Top left: calibrator; bottom left: plug-in bays; top center: [[7000 series readout system|readout board]];  top right: Z amplifier  
+
7904-left.jpg | Left side. Left top: Vertical amplifier; left bottom: switch-mode power supply; right center: delay line; right bottom: plug-in bays
File:7904-right-front.jpg | Right side detail. Left: calibrator; right: readout.
+
7904-right.jpg | Right side.  Top left: calibrator; bottom left: plug-in bays; top center: [[7000 series readout system|readout board]];  top right: Z amplifier  
File:7904 interface 1.jpg|Plug-in interface board front (left piggyback board removed)
+
7904-right-front.jpg | Right side detail. Left: calibrator; right: readout.
File:7904 interface 2.jpg|Plug-in interface board rear
+
7904 interface 1.jpg|Plug-in backplane board front (left trigger selector piggyback board removed)
File:7904-x-amp.jpg | Horizontal (X) amplifier board
+
Tek7904-trig-selector.jpg | B Trigger selector piggyback board (A6)
File:7904-y-amp.jpg | Vertical (Y) amplifier board
+
Tek7904-vertical-interface.jpg | Vertical interface piggyback board (A7).  The two [[155-0095-03]] amplifiers (large metal cans) are used to select the signal from one vertical plug-in bay, and drive the delay line.
File:7904-z-amp.jpg | Z amplifier board
+
7904 interface 2.jpg|Plug-in backplane board rear
File:7904-controls.jpg | front-panel controls
+
Tek7904-backplane-bottom.jpg | Backplane board sandwich seen from below
File:7904_block.gif|7904 block diagram
+
7904-x-amp.jpg | Horizontal (X) amplifier board
 +
7904-y-amp.jpg | Vertical (Y) amplifier board
 +
7904-z-amp.jpg | Z amplifier board
 +
7904-controls.jpg | front-panel controls
 +
7904_block.gif|7904 block diagram
 +
Tek7904-7a19-7b92a-1010mhz-hfsync.jpg | A 7B92A (B098xxx) displaying a 1.01 GHz sine in HF Sync mode ([[7904]] mainframe, [[7A19]] amplifier).
 +
 
 +
</gallery>
 +
====Power Supply====
 +
<gallery>
 +
7904-psu-internal.jpg    | 7904 switchmode power supply, covers removed
 +
7904-psu-right.jpg        | View from right (as seen from front of instrument)
 +
7904-psu-primary.jpg      | Primary side circuit board
 +
7904-psu-primary-caps.jpg | Primary side capacitors
 +
7904-psu-transformer.jpg  | Detail view of transformer from the side
 +
7904-psu-rectifier.jpg    | Secondary side rectifier board
 +
7904-psu-regulator.jpg    | Secondary side post-regulator
 
</gallery>
 
</gallery>
 +
 
===7904A===
 
===7904A===
 
<gallery>
 
<gallery>
File:7904A_1.JPG|7904A
+
7904a-front.jpg |7904A
 +
7904A_rear.jpg |7904A Rear
 +
7904A_top1.jpg |7904A Top with Horizontal Amplifier at top right
 +
7904A_right1.jpg |7904A Right with Z-axis on top right and 2nd Gen. Readout board at bottom right
 +
7904A_left1.jpg |7904A Left with Vertical Amplifier (top) and Vertical switch board (bottom)
 +
7904A_topleft1.jpg |7904A Topleft
 +
7904A_left_closeup.jpg |7904A Closeup of Vertical amplifier
 +
7904a lvps1.png|7904A Low-voltage Power Supply Schematic
 +
7904a-h-v.jpg | 7904A Horizontal and vertical amplifiers
 
</gallery>
 
</gallery>
  
  
 
[[Category:7000 series non-storage mainframes]]
 
[[Category:7000 series non-storage mainframes]]
 
__NOTOC__
 

Latest revision as of 21:35, 10 March 2021

Manuals – Specifications – Links – Pictures

The Tektronix 7904 is a 500 MHz, non-storage 7000-series oscilloscope mainframe with four bays. It accepts two 7000-series vertical plug-ins and two 7000-series horizontal plug-ins. It was introduced in late 1971/early 1972 (Note 1). The successor model 7904A was introduced in 1984. There is also a rack-mount version, the R7903, albeit with only one horizontal bay.

Performance is largely determined by the plug-ins. The 7A19 vertical amplifier and 7B92 time base were introduced along with the 7904 to match the 500 MHz system bandwidth.

Design Staff of 7904 Project (from July 1971 Tekscope):

Specifications

Bandwidth 500 MHz
Fastest calibrated sweep 500 ps/Div (with 7B92A, other time bases "uncalibrated for first 60 ns")
Acceleration voltage 24 kV (+21 / -3 kV)
Calibrator (7904) 4 mV, 40 mV, 400 mV, 4 V or 40 V (p-p) into 1 MΩ; 2 mV, 20 mV, 200 mV or 400 mV into 50 Ω; or 40 mA; selectable 1 kHz, ½ rep. rate of B Sweep Gate, or DC
Calibrator (7904A) 4 mV to 4 V (p-p) in decade steps, 1 kHz; 40 mV to 400 mV into 50 Ω
Power consumption 190 W
Weight 13.5 kg (30 lbs)
CRT Options

7904A differences

The 7904A re-implements the vertical amplifier using Hypcon-packaged amplifier chips designed for the 7104, such as the 155-0178-00.

The 7904 had an elaborate 5-decade built-in calibrator with variable rate that was dropped from the 7904A. The rear remote control connector unique to the 7904 was dropped as well. In the 7904A, The Control Illumination switch moved to the rear panel, and the readout system gained a pulsed mode in which it is synchronized with the sweep instead of interrupting the display at random times. This pulsed mode is not compatible with all time base plug-ins (see manual p. 1-12).

Options

  • Opt.2: X-Y delay compensation network
  • Opt.3: Extra EMI shielding
  • Opt.4: Maximum-brightness CRT with reduced area
  • Opt.78: P11 phosphor

Operation

The 7904 has many modes of operation. One mode is called "Independent-Pairs Display" in the manual, where the input to the left vertical plug-in is displayed using the B horizontal time-base plug-in, and the input to the right vertical plug-in is displayed using the A horizontal time-base plug-in. This resembles the trace-slaving "ALT" mode that is produced by an 1A4 in a 547. Many other modes are available. It is possible to put vertical plug-ins in the horizontal slots for X-Y operation. It is even possible to put a horizontal plug-in in one of the vertical slots to produce a raster scan.

A special plug-in, the 7A21N, provides direct access to the deflection plates up to 1 GHz at an uncalibrated sensitivity of 4 V/Div. This plugin requires modifications to the mainframe to bypass the Y output amplifier (thus disabling readout and the other vertical plugin bay).

A rear-panel remote control connector has connections for single-sweep ready lamps, a reset button, and readout control.

Internals

The 7904 uses a switch-mode power supply and has no fan. It incorporates a 65 ns Y delay line. This delay is too short for some older time bases such as 7B53 to display the trigger event.

Thor Hallen designed the main vertical amplifier and the 7A19 plugin (Note 1). It used bridged T coils and the "ft doubler" circuit patented by Carl Battjes to achieve its bandwidth.

The 7904 makes extensive use of custom integrated circuits and hybrid circuits, inter alia, the 155-0064-00 470-ps output amplifier, 155-0022-00 analog multiplexer for channel switching, 155-0059-00 HF amplifier, 155-0095-01 and 155-0095-03 differential HF amplifiers, and 155-0067-02 SMPS controller.

The 7904A includes 155-0173-05, 155-0175-05 and 155-0178-05 amplifiers.

The signal path is completely differential and the internal signal wiring is 50 Ω coax. The CRT (154-0644-05) has distributed vertical deflection plates.

Prices

  Year 1972 1976 1980 1984 1990
Model 7904 7904 7904 7904A 7904A
Mainframe only Catalog price $2,900 $4,100 $6,265 $8,810 $12,750
2019 value $17,640 $18,320 $19,330 $21,550 $24,800
Mainframe with 7A19,
7A19 Opt. 04, 7B92
Catalog price $5,500 $7,765 $12,015 $17,425 $24,190
2019 value $33,450 $34,690 $37,070 $42,630 $47,050

Links

Notes

  1. See 7A11 and John Addis, Good Engineering and Fast Vertical Amplifiers, in Jim Williams (Ed.), Analog Circuit Design: Art, Science and Personalities (1991), p.114, and Tektronix New Products 1972 brochure.

Pictures

7904 non-A

Power Supply

7904A