Tektronix AM503: Adjustment

Having put the Tek AM503 with the 4 MHz oscillation (B075593) on the shelf pending arrival of what might be the world’s last remaining NOS 2625 op amp in the “screened and tested” 156-0317-03 grade, I figured I might as well go through the adjustment procedure on one of the bench units (B064098) to reset the gain and reduce the peaky leading edges (green trace):

Tek AM503 - B031510 B064098 - 10mA-div
Tek AM503 – B031510 B064098 – 10mA-div

I conjured a low-budget Special Adapter to feed signals into the front-panel connector:

Tektronix AM503 Special Adapter
Tektronix AM503 Special Adapter

I also used a somewhat smaller resistor in place of the required 3 Ω 3 W wire-wound unit:

Tek AM503 - 3 ohm test resistor
Tek AM503 – 3 ohm test resistor

It need only soak up a few seconds of the degaussing signal and never even got warm, so it’s all good.

To my surprise, the square-wave output of the JDS6600 Function Generator meets the 10 ns risetime requirement:

JDS6600 Fn Gen - risetime 50 ohm
JDS6600 Fn Gen – risetime 50 ohm

Perhaps half an hour of adapter shuffling and trimmer twiddling later, the AM503 output looked better:

Tek AM503 - compensation adj
Tek AM503 – compensation adj

The (purple) input comes from the function generator output through a BNC tee and an unterminated foot of coax, so the leading edge ringing is perfectly normal.

With the scope input now providing the 50 Ω termination and the Hall probe clamped around one wire of a clip-to-clip pair of BNC-to-alligator-clip adapters, we’re still not talking RF-grade interconnection quality:

Tek AM503 - 1 MHz square
Tek AM503 – 1 MHz square

Even through it’s not factory spec, the output tracks the input well enough for my simple needs.

Good old Tek instruments: gotta love ’em!