Philips GM2882 signal generator (1946?)

The GM2882 is an RF generator covering frequencies from 100 kHz to 60 Mhz. The documentation I found dates from 1946. Some time after I acquired this one, I bought a still older GM2882 version that will need some work before it will work again.

It comes in a steel case with rounded corners, coated with black wrinkle finish. This style of case has been used by Philips for their measuring instruments from the late 1930's until the late 1940's. The valves used fit into the time frame of about 1942 to 1948:

• EF50 as RF oscillator
• EF50 as modulator
• EF6 as LF oscillator
• EZ2 as rectifier.

Both the EF6 and EZ2 have a P (side contact) base. These types have been introduced around 1937. The EF50 is an excellent HF valve, having a B9G base having low stray capacitance for valves with good HF characteristics. The EF50 has been developed early in WW2 and has been used in military equipment and measuring equipment during and shortly after the war.

This generator is neatly built. The range switch is a carrousel that plugs the right set of inductors for the selected range into the oscillator circuit. This reduces stray self-inductances and capacities compared to a rotary switch with its wiring and results in a stable oscillator. The tuning capacitor is driven by a tuning cord. The carrousel and tuning capacitor are placed in shielded compartments.

This generator does not have a regulated power supply. Nevertheless, Philips claims it should have a stability of better than 0,1 % after warming up.

The EZ2 rectifier is a nice valve to look at when it is working. I tried to capture the glow of the cathode but my Sony camera seemed to have problems with glowing objects at low lighting conditions. On the picture, the cathode showed up as a purple object and the camera couldn't focus on it. It may be that the blue pixels are sensitive to infrared light.

I bought this GM2882 on the quarterly NVHR swapmeet in 2004. It was looking all right, and I thought it would be a nice replacement for the rather unstable Taylor 67A generator I used before. When I tried it, it turned out to work fine.

Later on, in 2006, I bought a GM2883, an even more stable and advanced RF generator by Philips. A few months later I sold the GM2882 to a fellow hobbyist who needed a generator like this to align his old radios.