AM503: Difference between revisions

* [http://w140.com/smb/AM503_SM.pdf Tektronix AM503 Manual (OCR, PDF)]

* [http://w140.com/am503a_service.pdf Tektronix AM503A Manual (PDF)] (no schematics)

The high frequency amplifier was differential to accommodate an oscilloscope’s differential input.   

The last change was the output stage that was added to convert the differential circuit to single ended, and then output that to a front panel BNC.  

The AM503 was also intended to work with future higher frequency probes, like the [[P6022]] with an added hall device for DC measurements.   

The smaller P6022 had a 120 MHz bandwidth, whereas the [[P6302]] was only 50 MHz.   

The AM503 was one of the first plug-ins for the TM500 line of products.   

It required more power than the current plug-in designs so the transformer and supply were changed in the TM500 frames early on just for the AM503.

There were some innovations that were incorporated in this design:   

The [[cam switch]] with replaceable laser trimmed attenuator resistors, a 1 GHz Gilbert cell op amp (actually developed by Howard Jones in 1963).   

The [[Peltola connector]], developed by Tek’s Ron Peltola,  a very low cost connector that worked well, even for the highest frequencies.   

A BNC was adapted to be used with the Peltola and is used on the front panel.

A large section of the AM503 was basically duplicating the front end of an oscilloscope since that was the original design intent,  

so it was thought later that the differential amp section could be eliminated and the amplifier made much smaller and even become part of a standalone probe.   

A prototype was created (author’s senior project at the University of Portland) but shelved, as there was no longer an engineer in Accessories for current probes.   

Much later it gave rise to the TCP series of stand-alone current probes.

The [[P6302]] and [[P6303]] probes utilized a Hall device that was manufactured in the clean room of the Accessories Manufacturing group.   

It was deposited onto a bar of ferrite that was later assembled into a U shape with other ferrite and potted in a mu-metal can along with the transformer bobbins.   

The cores were lapped and polished to a few Fresnel lines flatness to minimize the gap on the sliding ferrite.  

The L/R time constant affects the point where the Hall device and coils’ bandwidths crossover.

An interesting aspect of the design was trying to find a way to test and calibrate the peak current pulse on the larger P6303.   

Luckily we had the tube lab.  We developed an argon filled thyratron that could discharge a 4 kV charge line into a 4 Ω load.   

The 4 kV supply was charged into a 4 Ω transmission line so a clean high current pulse would be generated.   

This concept was taken from Tek’s [[109]] pulse generator.

A trigger circuit was designed to fire the grid.  It was based on the xenon flash circuit of the [[C-5|C5 camera]] flash, also in the Accessories group.

The first prototype I made arced across the laser trim lines in the metal film resistor as they were cut perpendicular to the current flow.   

We changed the laser trim to be parallel to the current path along the outside edges.     

That’s what was used in manufacturing for calibrating the risetime of the P6303.

Also interesting, the P6303 required special potting epoxy developed by 3M.   

The epoxy used in other current probes put excessive stress on the larger ferrite that caused the inductance to drop to zero.   

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==Pictures==

<gallery>

Tek am503 t1.jpg | AM503

Tek am503b tm502a 1.jpg| Two AM503B in a [[TM502A]]

</gallery>