The Tektronix RM503 is a single trace,
low frequency, non-storage oscilloscope in a rack mount chassis.
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,
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
(There is a .001 μF blocking capacitor and a 100 kΩ resistor to ground.)
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
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
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.
The power supply is regulated and operates in a switching mode. A line
transformer is used for an unregulated 500VDC supply that is used by a
regulated switching stage to generate the 3000VDC and other voltages
for the CRT.
Although only a single channel, this scope has dual differential input
amplifiers: one for the vertical axis and on for the horizontal. In
timed sweep mode, the horizontal amplifier is driven by the sweep and
timing generator. These differential amplifiers have matched nuvistor
triodes on thier inputs. These are small metal vacuum tubes about 3/8
inch in diameter. They are housed in an aluminum casting that provides
thermal stability. Unfortunately they are not so well matched any more
and the amplifiers don't balance at higher gains.