Philips GM2886-01 sweep generator

The GM2886 is a "wobbulator", an RF sweep generator. It has an oscillator that can be frequency modulated. It has are only 2 controls: a variable capacitor to set a frequency offset and a potmeter to control modulation depth. As a modulating signal, the deflection signal of a scope is used. Accordingly, the GM2886 requires a 50V_tt external sweeping signal.

In order to build a stable oscillator with a constant sweep, Philips has the oscillator operate at a fixed frequency of 4 MHz. The signal is then mixed in a frequency converter with the output signal of a conventional RF generator.

The GM2886-01 is a modernised version of the GM2886. The -01 has a regulated power supply, whereas the GM2886 only has a neon stabiliser for the oscillator. And the valves are more modern. The GM2886 uses noval and rimlock types, but the the GM2886-01 has replaced all the rimlock types by noval valves. The valves used in the GM2886-01 are:

• ECH81 as oscillator and mixer.
• ECH81 as reactance valve.
• OB2 neon voltage reference.
• ECC81 as power supply regulator
• EZ80 rectifier

I bought this instrument through Internet from a trader. It looked ok. The coaxial output cable at the back was in good shape and there were no signs of rust. The valves inside looked practically new, apart from a thin cover of dust.

This instrument must date from the late 1950's. The documentation I found is from 1955. The steel case with rounded corners and grey hammered metal finish has been used by Philips for instruments from around 1949 up until 1960 or so.

On the inside, though, it was in splendid condition. The rectifier seems like new.

I tested it with a scope and frequency counter and all seemed to be well. But I'll have to get my hands on a working oscilloscope of the same age to be able to use it.