Philips GM5606 oscilloscope

This scope dates from the early sixties. It contains 21 valves, which includes the DN10-78 CRT. A special design feature is that the vertical and horizontal amplifiers are completely balanced and DC coupled, which is something special for a scope with valves. The CRT has a 10 cm round screen.

The specified vertical 3 dB bandwidth is DC to 300 kHz, so it is intended for LF use only. The most sensitive range is 10 mV/cm The limited bandwidth is due to the large amplification per stage.

The timebase is built up around a Schmitt-trigger circuit followed by a Miller integrator. It has free-running and triggered modes. Ranges are 2,5 μs to 1 s/cm.

I got this scope in 1979 from a neighbour who knew about my electronics hobby. He told me it was practically impossible to repair because the mains transformer was damaged. I sincerely hoped he was wrong and that I would be able to fix the scope.

I was able to obtain a copy of the manual at the electronic equipment maintenance service at the Delft University. This helped me to find out how the scope worked. The neighbour was right about the power transformer. The scope has a simple power supply that gets its HV from a 650 V winding on the mains power transformer. This winding turned out to be interrupted. I could confirm that the rest of the scope was ok by adding an extra transformer, a mains transformer from an old radio that delivered 2*325 V. Unfortunately, there is no space to house an extra transformer and having an extra transformer dangling at the back of a scope is impractical and dangerous.

Rewinding the transformer is not really an option, so in the end, this scope was not usable. I decided to keep it as a curiosity.