Check the listing for details. Tektronix AM 503 Current Probe Amplifier. Condition: For parts or not working. Listed at 100.00 USD. Up for sale here is this Tektronix AM 503 Current Probe Amplifier. This came from the estate of a vintage stereo tech. It was in regular use at one point but I do not know if it is currently working, so I am listing it as non-working. The little pull knob part is not attached, but there is either the missing knob or a replacement or something tucked into a bag. I don't know how replaceable that part is, but this was previously installed in a case and I was able to remove it without issues, for what that's worth. From the back I can see that one capacitor was replaced at some point. This is completely untested and is sold as non-working, for parts/repair. Please see my pictures for details. US shipping and handling is $20. If you have any questions, please ask. I have other test equipment and other vintage electronics listed--feel free to take a look!