7A12: Difference between revisions

Revision as of 15:44, 30 September 2024

Tektronix 7A12
120 MHz dual-channel amplifier 7A12 front view Compatible with 7000-series scopes Produced from 1969 to 1974 Manuals Tektronix 7A12 Manual (OCR) Alternate Tektronix 7A12 Manual @ BAMA (All manuals in PDF format unless noted otherwise)

Manuals – Specifications – Links – Pictures

The Tektronix 7A12 is a 120 MHz dual-trace vertical plug-in for 7000-series scopes. This original 7000-series plugin allows large dc offset voltages, however the offset voltage is not available on the front panel to be measured externally as with the 7A11.

Switches on the front panel control miniature relays in the signal path to select input attenuators, through logic circuits.

The 7A12 was designed by Roy Hayes (who also designed the 3A3 and 3A8 before leaving for HP Loveland in Jan 1971). The Evaluation Engineer for the 7A12 was Peter Starič, co-author of the book "Wideband Amplifiers" with Erik Margan. Peter and his daughter, Zorana, returned to Ljubljana on August 4, 1970.

Key Specifications

Bandwidth	120 MHz (79xx) / 105 MHz (77xx) / 55 MHz (74xx)
Deflection	5 mV/Div to 5 V/Div (1–2–5), variable up to 12.5 V/Div
Input impedance	1 MΩ // 24 pF
Timing	Delay difference between channels < 500 ps
Channel isolation	At least 3000:1 at 75 MHz
Maximum input	350 V DC + Peak AC at 1 kHz or less
DC offset	At least ±500 divisions

Internals

The 7A12 uses the 155-0032-00 custom IC as a gain stage and the 155-0022-00 for channel switching.

John Addis writes: There were two mistakes, concept errors, that doomed the 7A12 from day one. The first was in deciding to use the 1 GHz F_T Tektronix IC process (called 50/450 for resistivities of the two base layers) for the signal path. This process was Tektronix' fastest but too slow for a plugin expected to provide 150 MHz bandwidth in the fastest original mainframe, the 7704. At the time, HP had a 2.5 GHz process used in the 1830A, 250MHz plugin.

The second day one mistake, later pointed out by Tom Rousseau, was to arrange the two channels side by side. Roy wanted to be able to go from one sensitivity (deflection factor) to another without having to go through all the sensitivities in between as happens with a rotary switch. The vertical row of push buttons was functionally attractive. However, that would require both channels to occupy the same space if on a single, centered, vertical circuit board.

The solution was two separate, mirror image attenuators and two identical amplifier boards all attached to a main vertically-centered circuit board. Having two mirror image attenuators was obviously very expensive.

The two identical amplifier circuit boards, one mounted on each side of the center board, are cleverly flipped so both face outward from the center board. This is accomplished by having one near the top rail and the other near the bottom rail.

As part of the 7403 program to bring a low cost entry product into the 7K series of plugins, Tom Rousseau was assigned to design a new dual trace plugin with discrete components. One channel was physically above the other. This was all done on a single circuit board, had only 80 MHz bandwidth but was much less expensive to manufacture. The design was classical, had none of the complicated offset circuitry, and the channel switch was the same venerable 155-0022-00 used in the 7A12. It became the 7A18.

Tom Rousseau writes: "After the 7A18 project, and becoming familiar with the M84(155-0078-xx) IC, I conjured up the 7A26 concept based on the general layout of the 7A18. I figured that with the M84, I could more than double the bandwidth of the 7A18 and provide a reasonably higher bandwidth, 1M Ohm dual trace plug-in. Further, I offered the possibility of making four vertical plug-ins from one basic design: 7A26, 7A24 (50 Ohm), 7A16A (1M Ohm, single channel) and a fourth not pursued, 7Axx, single channel, 50 Ohm. I worked on this for awhile then popped the idea to management (Oliver Dalton), who agreed to three of the plug-ins."

The 7A26 became the best selling Tektronix plugin of all time. Tektronix literally gold plated a 7A26 and gave it to Tom in recognition.

See https://vintagetek.org/100000-7a26-plug-in/

Links

Documents Referencing 7A12

Document	Class	Title	Year	Links
Tekscope 1969 V1 N5 Oct 1969.pdf	Article	Introducing the New Generation	1969	7000-series scopes • 7504 • 7704 • 7A11 • 7A12 • 7A13 • 7A14 • 7A16 • 7A22 • 7S11 • 7M11 • 7B50 • 7B51 • 7B70 • 7B71 • 7T11 • R5030 • 7000 series readout system • Miniature relays • Cam switches • Industrial Design • T7500 • T7700 • P6052 • P6053 • C-50 • C-51 • 204-2
Tekscope 1969 V1 N6 Dec 1969.pdf	Article	A New Logic for Oscilloscope Displays	1969	7000-series scopes • 7A11 • 7A12 • 7A13 • 7A14 • 7A16 • 7A22 • 7B50 • 7B51 • 7B70 • 7B71 • 7S11 • 7T11 • 7504 • 7704
7000 series brochure March 1973.pdf	Brochure	7000 series brochure, March 1973	1973	7A11 • 7A12 • 7A13 • 7A14 • 7A15A • 7A16A • 7A17 • 7A18 • 7A19 • 7A21N • 7A22 • 7B50 • 7B53A • 7B70 • 7B71 • 7B92 • 7CT1N • 7D11 • 7D13 • 7D14 • 7D15 • 7M11 • 7L12 • 7S11 • 7S12 • 7T11 • 7704A • R7704 • 7904 • R7903 • 7603 • R7603 • 7403N • R7403N • 7313 • R7313 • 7613 • R7613 • 7623 • R7623 • P7001

Pictures

Front view
Front view
Attenuator schematic with relays
7A12 Amplifier PCB
Left side view

Components

Some Parts Used in the 7A12

Part	Part Number(s)	Class	Description	Used in
148-0034-01	148-0034-01	Discrete component	miniature DPDT relay	485 • 7A12
148-0034-02	148-0034-02	Discrete component	miniature DPDT relay	7A12
155-0022-00	155-0022-00 • 155-0022-01	Monolithic integrated circuit	analog multiplexer	147 • 148 • 149 • 335 • 468 • 1430 • 1441 • 1461 • 1900 • 1910 • 2220 • 2221 • 2230 • 5223 • 5403 • 5440 • 5441 • 5443 • 5444 • 5A38 • 7313 • 7403N • 7503 • 7504 • 7514 • 7603 • AN/USM-281C • 7613 • 7623 • 7623A • 7633 • 7704 • R7704 • 7704A • 7834 • 7844 • 7854 • R7912 • 7912AD • 7912HB • 7904 • R7903 • 7904A • 7934 • 7A12 • 7A18 • 7A18A • 7A18N • 7B52 • 7B53N • 7D10 • 7D11 • 7D12 • NT-7000 • P7001
155-0032-00	155-0032-00 • 155-0032-01	Monolithic integrated circuit	variable-gain transconductance amplifier (voltage in, current out)	335 • 464 • 465 • 465B • 466 • 475 • 475A • 475M • 634 • 650 • 651 • 652 • 653 • 655 • 656 • 670 • 671 • 7A12 • 475 • FG504 • 1440 • 1460 • 1480 • 1481 • 1482 • 1485

@@ Line 44: / Line 44: @@
 The two identical amplifier circuit boards, one mounted on each side of the center board, are cleverly flipped so both face outward from the center board. This is accomplished by having one near the top rail and the other near the bottom rail.
-Tom Rousseau designed a new dual trace plugin with discrete components.  One channel was physically above the other. This was all done on a single circuit board, had only 80 MHz bandwidth but was much less expensive to manufacture. The design was classical, had none of the complicated offset circuitry, and the channel switch was the same venerable 155-0022-00 used in the 7A12. He did this on his own, not at management's request.  Management liked it and it became the [[7A18]].  Later Tom had the advantage of a 3 GHz IC process (SHF2).  He used the [[M84]] (155-0078-xx), already in production for the [[485]].  This was the 200 MHz [[7A26]].  It became the best selling Tektronix plugin of all time.  Tektronix literally gold plated a 7A26 and gave it to Tom in recognition.
+As part of the 7403 program to bring a low cost entry product into the 7K series of plugins, Tom Rousseau was assigned to design a new dual trace plugin with discrete components.  One channel was physically above the other. This was all done on a single circuit board, had only 80 MHz bandwidth but was much less expensive to manufacture. The design was classical, had none of the complicated offset circuitry, and the channel switch was the same venerable 155-0022-00 used in the 7A12. It became the [[7A18]].
+[[Tom Rousseau]] writes: "After the 7A18 project, and becoming familiar with the [[M84]](155-0078-xx) IC, I conjured up the 7A26 concept based on the general layout of the 7A18.  I figured that with the [[M84]], I could more than double the bandwidth of the 7A18 and provide a reasonably higher bandwidth, 1M Ohm dual trace plug-in.  Further, I offered the possibility of making four vertical plug-ins from one basic design:  7A26, 7A24 (50 Ohm), 7A16A (1M Ohm, single channel) and a fourth not pursued, 7Axx, single channel, 50 Ohm.  I worked on this for awhile then popped the idea to management ([[Oliver Dalton]]), who agreed to three of the plug-ins."
+The 7A26 became the best selling Tektronix plugin of all time. Tektronix literally gold plated a 7A26 and gave it to Tom in recognition.
 See https://vintagetek.org/100000-7a26-plug-in/