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{{Plugin Sidebar | |||
| manufacturer=Tektronix | |||
| series=560-series scopes | |||
| type= 2A61 | |||
| summary = Differential amplifier plug-in | |||
| image=Tek 2a61 front.jpg | |||
| caption=Tektronix 2A61 Front | |||
| designers=Larry Mayhew | |||
| introduced=1963 | |||
| discontinued=(?) | |||
| manuals= | |||
* [[Media:070-0328-01.pdf|Tektronix 2A61 Manual]] (OCR) | |||
* [[Media:2a61 1000-1 cal input adapter.pdf|Tektronix 2A61 1000:1 Cal Div/Input Adapter (OCR)]] | |||
}} | |||
The '''Tektronix 2A61''' is a high gain differential AC amplifier plug-in for the [[560-series scopes | 560 series oscilloscopes]], [[introduced in 1963]]. It has independently switchable low frequency and high frequency limits. The low frequency limit can go well below 1 Hz, but it can't go to DC. | |||
{{BeginSpecs}} | |||
{{Spec | Input impedance | 1 MΩ // ~100 pF }} | |||
{{Spec | Deflection | 10 μV/div to 20 mV/div in 1−2−5 sequence }} | |||
{{Spec | Bandwidth | Switch selectable:<br>Low Limit: ~0.06 to ~600 Hz<br>High Limit: ~60 Hz to ~0.3 MHz }} | |||
{{Spec | CMRR | 50,000:1 at Frequencies below 10 kHz }} | |||
{{Spec | Common Mode Range | -5 V to 5 V in A-B mode}} | |||
{{Spec | Input DC Bias | Max: ±0.1 V differential }} | |||
{{Spec | Line Filter | Switchable: at Least 50:1 attenuation }} | |||
{{EndSpecs}} | |||
==Internals== | |||
The front end consists of a differential amplifier. | |||
Up to serial number 986, the front-end differential amplifier used a pair of [[5842]] tubes biased with a tail current of 10 mA and a plate-to-cathode voltage of about 100 V. | |||
[[File:2a61 frontend.png|thumb|left|upright|[[Nuvistor]]-based front-end amplifier]] | |||
Starting with serial number 987, the front-end differential amplifier was made with four [[7586]] [[nuvistor]] triodes: V424, V425, V524, and V525. | |||
The parallel combination of V424 and V425 forms one side of the differential amplifier and the parallel combination of V524 and V525 forms the other side. | |||
However, for purposes of thermal stability, V424 is thermally connected to V524 and V425 is thermally connected to V525. | |||
The tail current in the 987-and-up version is about 16 mA and the nuvistors have a plate-to-cathode voltage of about 70 V. | |||
The second gain stage is a differential amplifier made of a pair of a pair of germanium PNP transistors. | |||
To implement the low-frequency cutoff, the 2A61 has a large electrolytic capacitor, C437 (13,000 μF or 20,000 μF depending on serial number), | |||
in the emitter frequency compensation network of the second differential amplifier stage. | |||
Although C437 is polarized, it is operated with no DC bias and therefore sees reverse voltage as part of normal operation. | |||
D437 and D438 shunt C437, preventing it from ever seeing a voltage more than one diode drop. | |||
Most electrolytic capacitors are specified to handle reverse voltages of at least 1 V without damage. | |||
The 2A61 manual's calibration instructions recommend using the Heathkit IG-72 Audio Generator. | |||
A suitable input connector for the 2A61 is a PC06 8-4P / MS3106 8-4P. | |||
The standard cable for connecting the input signal to the 2A61 is the [[012-072]]. | |||
==Pictures== | |||
<gallery> | <gallery> | ||
Tek 2a61 front.jpg | Front | |||
Tek 2a61 left.jpg | Left | |||
Tek 2a61 right.jpg | Right | |||
Tek 2a61 top.jpg | Top | |||
Tek 2a61 bottom.jpg | Bottom | |||
Tek 2a61 1.jpg | |||
Tek 2a61 2.jpg | |||
Tek 2a61 3.jpg | |||
Tek 2a61 4.jpg | |||
Tek-2a61 early.png | Schematic (early version) | |||
Tek-2a61 late.png | Schematic (late version) | |||
</gallery> | </gallery> | ||
[[Category:560 series plugins]] |