7A29

Template:Plugin Sidebar 2 The Tektronix 7A29 is a 1 GHz single-channel vertical plug-in for 7000-series scopes. It is primarily intended for the 7103 and 7104. Like with the 7A19, a variable signal delay was available as an option.

There is also a 7A29P, which has digitally programmable gain, intended for the 7000 series digitizers and the 7854 only.

The 7F10 uses the 7A29's amplifier board after the optical/electrical converter.

Key Specifications

Bandwidth	1 GHz (in 7104)
Input impedance	50±1 Ω, VSWR <1.2:1 from DC to 1 GHz (10 mV/Div: 1.4:1, Opt.4: 1.5:1)
Max. input	max. 10 VRMS or 1 Ws pulses not exceeding 50 V; max. 100 V additional DC component in AC mode
Deflection	10 mV/div to 1 V/div, 1-2-5, ±2%; variable 2.5:1
Channels	Single channel
Recommended probes	P6056 (×10), P6057 (×100)
Options	Option 4: variable delay (1 ns)

Internals

The 7A29 employs a number of Tek-made custom Hypcon-packaged hybrids, the 155-0180-00 fast input protection, 155-0181-00 input amplifier and 155-0175-00 trigger amplifier (2 ×).

It uses a "feed-beside" scheme implemented with standard low-frequency operational amplifiers to compensate for low-frequency anomalies in the frequency response that are attributed to transistor heating.

The input connector is a special Tek-made part that is exactly 50 Ω. Typical BNC connectors are around 52 Ω.

The 7A29 does not use the ±50 V supplies provided by the mainframe.

Although the 7A29 has a VARIABLE gain control, this control has the undesirable side-effect of also affecting bandwidth. See bandwidth versus VARIABLE gain plot below.

Links

• Tektronix 7A29 teardown - nice detailed pictures of attenuator internals
• Tek 7A29P @ amplifier.cd including internal pictures

Pictures

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  7A29 (no opt.) front

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  7A29 Opt.4 front

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  7A29P

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  7A29P

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  photo of 7A29 from manual (standard and option 4 units)

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  7A29 bandwidth versus variable gain

Internal

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  7A29 (no opt.), left side (fixed delay line)

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  7A29 Opt.4, left view (variable delay line enclosure above PCB)

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  7A29, right side

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  7A29 input protection relay

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  7A29 input protection relay lever

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  7A29 backplane connector (stripline signal path)

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  7A29 amplifiers

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  7A29, right side, rear

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  7A29, right side, front

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  7A29P right

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  7A29P left

Schematics

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  input amplifier schematic

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  output amplifier schematic

Measurements

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  Sample 7A29 rise time measurement (Source: S-52) - 320 ps equiv. 1.09 GHz system bandwidth including 7104 mainframe