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The Tektronix 122 is an external low-level preamplifier. | {{Instrument Sidebar | ||
|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 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. | |||
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 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> | |||
Tek 122 x.jpg|early model | |||
Tek 122 x2.jpg|early model | |||
Tek 122 front.jpg|early model | |||
Tek 122 power.jpg|early model | |||
Tek 122 front close.jpg|early model | |||
Tek 122 bottom inside.jpg|early model | |||
Tek 122 top inside.jpg|early model | |||
Tek 122 schem.png | schematic | |||
Tek 122 int right.jpg|late model | |||
Tek 122 int panel.jpg|late model | |||
Tek 122 late int left.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> | |||
==Components== | |||
{{Parts|122}} | |||
[[Category:Amplifiers]] | |||