Equipment/BBC AF signal generator

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BBC AF signal generator

siggen, Click for bigger picture

This belongs to Russ. You can use it but Russ will be grumpy if it gets damaged.

Quickstart to produce an audio tone: select 100-100K range, Frequency dial at 6 gives roughly middle C (720Hz). Gain knob on rear at 2. Front output knob up 20 degrees. Sweep off. modulation off. Rear on/off switch on. Front on/off switch on.

Beware This unit has a built in amplifier. The loudspeaker terminals on the back can produce up to 40volts pk-pk. You can blow up things like computer audio inputs!

The loudspeaker terminals on the back can produce a lot more current than a typical 600ohm signal generator output.

The low level audio output requires a quarter inch jack plug. There isn't one handy with the unit.

It contains an ILP amplifier module. It my experience the overload protection on those would not protect it from all possible loads. It may be easier to blow up than a typical 600ohm signal generator output.

The 100-100K range seems most usefull, other ranges seem to be mostly below what little loudspeakers can produce.

The frequency dial is a bit wobbly and dosn't stop distinctly at the ends of it's travel. The variable resistor inside may not be in top mechanical condition.


This unit was made sometime around 1989 and looks like it was built from modules from the RS catalogue. Russ purchased it from an auction of old BBC equipment.

siggen rear panel


June 2011. Someone reported it not working, supposedly one of the fuses on the back was blown and blew again when replaced. The two fuses on the right hand of the rear panel supply +45volts and -45volts to the amplifier module. The +ve fuse was ok and is a 2amp T fuse. A 250mA fastblow fuse had been fitted in the other holder. Seems fine with a 2amp T fuse.