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The Tektronix 122 is an external low-frequency low-level preamplifier. The low-frequency cutoff and high frequency cutoff can be selected. 40kHz is the highest cutoff.  The input is differential, using an XLR
{{Instrument Sidebar
pro-audio style connector.  The output is through a UHF (SO-239) connector, single-ended.  The amplifier electronics are on a plastic board with metal studs where components are soldered in place.  The board is mechanically isolated from the case by four rubber bushings.   
|manufacturer=Tektronix
|model=122
|class=Amplifier
|series=
|summary=low-level preamplifier
|image=Tek 122 x.jpg
|caption=Tek 122 early model
|introduced=1950
|discontinued=(?)
|designers=
|manuals=
* [[Media:070-246.pdf|Tektronix 122 and 125 Manual]]
* [https://w140.com/brophy_122_mod.pdf Low Noise Modifications of the 122]
}}
The '''Tektronix 122''' is an external low-frequency low-level preamplifier.   


The 122 has four stages of amplification.  The first stage is a direct-coupled differential amplifier formed by both halves if a [[12AX7]] dual-triode tube.  The total plate current of the input stage is about 450uA.  The second stage is a [[12AU7]] differential amplifier, differentially driven by the first stage.  There are DC blocking capacitors between plates of the first stage and the grids of the second stage.  The second stage is coupled to the third stage by capacitors, which can be switched to select the low-frequency cutoff frequency. The third stage is a common-cathode amplifier formed from one half of a 12AU7 dual triode tube.  The plate load resistors of the third stage amplifier are shunted by switchable capacitors, allowing the high-frequency cutoff to be selected.  The resulting signal is buffered by a cathode-follower stage formed from the other triode in the third stage's 12AU7 tube, biased at 1.8mA plate current. The output impedance is rated to be about 1000 ohms.
The low-frequency cutoff and high frequency cutoff can be selected.  40 kHz is the highest cutoff.   
The input is differential, using an [[XLR connector]].  The output is through a [[UHF connector|UHF (SO-239) connector]], single-ended.   
The amplifier electronics are on a plastic board with metal studs where components are soldered in place.   
The board is mechanically isolated from the case by four rubber bushings. The 122 is the only Tektronix product ever made that has a rotary two position power switch.


For low noise performance and freedom from oscillations, the power supplies in the 122 are carefully bypassed.  The B+ supply of +135VDC (along with -90VDC and +6VDC) comes into the 122 through an octal connector.  The raw voltage coming in is used for the plate supply of the output (fourth) stage.  That voltage is low-pass filtered to produce voltage "C" which is used as the plate supply for the third stage.  Voltage "C" is low-pass filtered to produce voltage "B", the plate supply for the second stage.  Finally, voltage "B" is low-pass filtered to produce voltage "A", the plate supply for the first stage.  The result is that the sensitive first and second stages have well filtered plate supplies.  This technique is also seen in other gear from the era, such as the McIntosh MC-30 audio power amplifier.
The 122 has four stages of amplification.   
The first stage is a direct-coupled differential amplifier formed by both halves if a [[12AX7]] dual-triode tube.   
The total plate current of the input stage is about 450 μA.   


* [http://bama.edebris.com/download/tek/122_125/Tek%20122_125.pdf Tektronix 122 and 125 Manual]
The second stage is a [[12AU7]] differential amplifier, differentially driven by the first stage.
* [http://w140.com/brophy_122_mod.pdf Low Noise Modifications of the 122 (PDF)]
There are DC blocking capacitors between plates of the first stage and the grids of the second stage.
The second stage is coupled to the third stage by capacitors, which can be switched to select the low-frequency cutoff frequency.  
The third stage is a common-cathode amplifier formed from one half of a 12AU7 dual triode tube.
The plate load resistors of the third stage amplifier are shunted by switchable capacitors, allowing the high-frequency cutoff to be selected.
The resulting signal is buffered by a cathode-follower stage formed from the other triode in the third stage's 12AU7 tube, biased at 1.8 mA plate current. 
The output impedance is rated to be about 1000 Ω. 


For low noise performance and freedom from oscillations, the power supplies in the 122 are carefully bypassed. 
The B+ supply of +135 V<sub>DC</sub> (along with -90 V<sub>DC</sub> and -6 V<sub>DC</sub>)
comes into the 122 through an [[octal connector]], typically from a Type [[125]] power supply.
(Note: The [[160]] power supply is not compatible. The voltages are quite different.)
The raw voltage coming in is used for the plate supply of the output (fourth) stage. 
That voltage is low-pass filtered to produce voltage "C" which is used as the plate supply for the third stage. 
Voltage "C" is low-pass filtered to produce voltage "B", the plate supply for the second stage. 
Finally, voltage "B" is low-pass filtered to produce voltage "A", the plate supply for the first stage. 
The result is that the sensitive first and second stages have well filtered plate supplies. 
This technique is also seen in other gear from the era, such as the McIntosh MC-30 audio power amplifier.
The power requirements of the 122 are:
* +135 V at 5 mA
* -90 V at 4 mA
* 6.3 V at 900 mA
The 122 appears in three form factors:
* 122 (standard, vertical orientation, no mounting ears)
* RM122 (rack mount, horizontal orientation, with wide front panel for mounting mounting in a standard 19" rack, later called "R122")
* FM122 (frame mount, vertical orientation, for use in the [[014-002]] mounting frame, later called "F122")
==Pictures==
<gallery>
<gallery>
Image:Tek 122 x.jpg|early model
Tek 122 x.jpg|early model
Image:Tek 122 x2.jpg|early model
Tek 122 x2.jpg|early model
Image:Tek 122 front.jpg|early model
Tek 122 front.jpg|early model
Image:Tek 122 power.jpg|early model
Tek 122 power.jpg|early model
Image:Tek 122 front close.jpg|early model
Tek 122 front close.jpg|early model
Image:Tek 122 bottom inside.jpg|early model
Tek 122 bottom inside.jpg|early model
Image:Tek 122 top inside.jpg|early model
Tek 122 top inside.jpg|early model
Image:Tek 122 schem.png
Tek 122 schem.png | schematic
Image:Tek 122 int right.jpg|late model
Tek 122 int right.jpg|late model
Image:Tek 122 int panel.jpg|late model
Tek 122 int panel.jpg|late model
Image:Tek 122 late int left.jpg|late model
Tek 122 late int left.jpg|late model
Image:Tek 122 late front.jpg|late model
Tek 122 late front.jpg|late model
Tek 122 system rs 1.jpg
Tek 122 system rs 2.jpg
Tek fm122 front.jpg|Tek FM122 front
Tek fm122 top connector.jpg|Tek FM122 top power connector
</gallery>
</gallery>
==Components==
{{Parts|122}}
[[Category:Amplifiers]]

Latest revision as of 11:15, 21 September 2023

Tektronix 122
low-level preamplifier
Tek 122 early model

Produced from 1950 to (?)

Manuals
(All manuals in PDF format unless noted otherwise)
Manuals – Specifications – Links – Pictures

The Tektronix 122 is an external low-frequency low-level preamplifier.

The low-frequency cutoff and high frequency cutoff can be selected. 40 kHz is the highest cutoff. The input is differential, using an XLR connector. The output is through a UHF (SO-239) connector, single-ended. The amplifier electronics are on a plastic board with metal studs where components are soldered in place. The board is mechanically isolated from the case by four rubber bushings. The 122 is the only Tektronix product ever made that has a rotary two position power switch.

The 122 has four stages of amplification. The first stage is a direct-coupled differential amplifier formed by both halves if a 12AX7 dual-triode tube. The total plate current of the input stage is about 450 μA.

The second stage is a 12AU7 differential amplifier, differentially driven by the first stage. There are DC blocking capacitors between plates of the first stage and the grids of the second stage. The second stage is coupled to the third stage by capacitors, which can be switched to select the low-frequency cutoff frequency. The third stage is a common-cathode amplifier formed from one half of a 12AU7 dual triode tube. The plate load resistors of the third stage amplifier are shunted by switchable capacitors, allowing the high-frequency cutoff to be selected. The resulting signal is buffered by a cathode-follower stage formed from the other triode in the third stage's 12AU7 tube, biased at 1.8 mA plate current. The output impedance is rated to be about 1000 Ω.

For low noise performance and freedom from oscillations, the power supplies in the 122 are carefully bypassed. The B+ supply of +135 VDC (along with -90 VDC and -6 VDC) comes into the 122 through an octal connector, typically from a Type 125 power supply. (Note: The 160 power supply is not compatible. The voltages are quite different.) The raw voltage coming in is used for the plate supply of the output (fourth) stage. That voltage is low-pass filtered to produce voltage "C" which is used as the plate supply for the third stage. Voltage "C" is low-pass filtered to produce voltage "B", the plate supply for the second stage. Finally, voltage "B" is low-pass filtered to produce voltage "A", the plate supply for the first stage. The result is that the sensitive first and second stages have well filtered plate supplies. This technique is also seen in other gear from the era, such as the McIntosh MC-30 audio power amplifier.

The power requirements of the 122 are:

  • +135 V at 5 mA
  • -90 V at 4 mA
  • 6.3 V at 900 mA

The 122 appears in three form factors:

  • 122 (standard, vertical orientation, no mounting ears)
  • RM122 (rack mount, horizontal orientation, with wide front panel for mounting mounting in a standard 19" rack, later called "R122")
  • FM122 (frame mount, vertical orientation, for use in the 014-002 mounting frame, later called "F122")

Pictures

  • early model

    early model

  • early model

    early model

  • early model

    early model

  • early model

    early model

  • early model

    early model

  • early model

    early model

  • early model

    early model

  • schematic

    schematic

  • late model

    late model

  • late model

    late model

  • late model

    late model

  • late model

    late model

  • Tek FM122 front

    Tek FM122 front

  • Tek FM122 top power connector

    Tek FM122 top power connector

Components

Some Parts Used in the 122

Part Part Number(s) Class Description Used in
12AU7 154-041 • 154-0041-00 • 154-0287-00 Vacuum Tube (Dual Triode) dual medium-μ triode 104 • 104A • 122 • 160 • 161 • 162 • 181 • 190 • 310 • 310A • 316 • 317 • 3C66 • 502 • 502A • 507 • 511A • 512 • 516 • 517 • 517A • 524 • 526 • 535 • 536 • 545 • 545A • 545B • 547 • 549 • 555 • 561 • 564 • 570 • 575 • 581 • 581A • 585 • 585A • C • D • E • N • Q • Hickok 1825
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