The Tektronix RM503 is a single trace, low frequency, non-storage oscilloscope in a rack mount chassis.

VR01-A

This scope was sold by DEC as the VR01-A Display Unit for use with point plot graphic options. I am curious about operational details. I found the most information in the AA11-D D/A subsystem manual, DEC-11-HAAC-D. The display is described as 45,000 points/second maximum and 50 points/second minimum. The upper limit is based on the amount of time necessary for deflection (20 μS) and intensification (2 μS). Of course there is no time left for any processing since the processor would be busy feeding it every point. The lower limit might be based on flicker, but that seems a little fast. At 50 refreshes/second, there is enough time for about 900 intensified points.

The Z-axis signals are -15 V for blanked, 0 V for low intensity, and +4.5 V for high intensity. The Z-axis signal is AC coupled and applied almost directly to the CRT grid. (There is a .001 μF blocking capacitor and a 100 kΩ resistor to ground.)

Specifications

• Type: single channel, non-storage
• Vertical and Horizontal Amplifiers: differential
• Input Impedance: 1 megΩ paralleled with 47 pF
• Bandwidth: DC to 450kHz
• Deflection Factors: 1 mV to 20 V/cm vertical and horizontal, 1, 2, 5 progression
• Sweep Time Base: 1 μs to 5 s/cm, 1, 2, 5 progression

This RM503

I found the scope on Ebay. It cost more to ship than to buy, so I guess I got an OK deal. It was quite clean  inside and out although though it looks like it might have moved around a few times.

The first thing to note is that this is pretty much an all tube scope. There are four transistors and a handful of semiconductor diodes, but the rest is all tubes. This was my first exposure to thermionics. Fortunately for me there was only one major problem, a failed resistor, and I tracked that down pretty quickly. That light blue resistor in the closeup at bottom right is bad.

The bezel surrounding the display is flat black. I have not seen an online picture of a scope with a black bezel. My guess is that this was an option for use with a scope camera to decrease reflection inside the camera.

The construction is basically point to point wiring with ceramic terminal blocks. The terminal blocks have notches that are plated with metal in such a way that they components can be inserted and soldered in place. There is a note explaining that silver solder must be used along with a spool of solder. The note explains that if tin-lead solder is used the plating will separate from the ceramic.

Oscilloscope Links

• Museum of Tek Scopes
• Classic Tektronix Scopes
• BAMA - Boat Anchor Manual Archive
• yahoo group TekScopes