Philips GM2317 signal generator

This is an LF generator. It ranges from 20 Hz to 250 kHz. I bought this signal generator from a collector just because it was interestingly old. But to my surprise it is still a useful instrument.

On the inside, it uses rimlock valves. The generator circuit is a Wien-bridge oscillator built around a 3-stage amplifier consisting of 2 EF40 and an EL41. Two incandescent lamps (ordinary lamps) are used in the feedback loop to stabilise the amplification and limit distortion (the specs say it should be under 2%). The power supply contains an AZ41.

This generator was in good condition. Though the coupling capacitor to the output valve was leaky, I did not replace it. The output valve is used as a cathode follower here, so the DC voltage on its control grid does not really change its working point much. After checking the capacitors and reforming the power supply electrolytics, I tried it and it worked right away.

Unfortunately, the generator is not as stable as it should be. The amplitude tends to vary and every now and then it suddenly starts to deliver a distorted signal. So I'll have to take a better look at it, some time.