Venner Electronics Wide Range Oscillator - Adding a transformer?

[AmmoJammo]

I have this old signal generator that I use just for audio ranges....

It originally ran off two 9volt batteries, but I wish to add a transformer.

From memory, the last time I attempted this, I got 50Hz hum as a result.

I've run it off an external 12volt plug pack before with no issues.

Should I be grounding the case to mains earth? or leaving it floating?

Anything else I should take into consideration before attempting to add a transformer, bridge rectifier, and filter capacitors again?

Thanks! (the 10,000uf capacitor was added last time I tried adding a transformer)

[edavid]

That's really beautiful.

You should try adding a simple regulator (LM317) to your power supply, that will reduce the 50Hz ripple a great deal.

[AmmoJammo]

I ended up finding a transformer from an old radio... It was actually centre tapped, using the taps in parallel with a diode on each, in the radio.

So, taps in series gave me about 13.6volts AC unloaded, resulting in 18volts DC once rectified, that dropped to 14volts with the load of the signal generator.

Ah well, close enough and it didn't cost anything.

However, this only seems to do 2volts rms output max... the 100mv range doesn't work, and the 10/1mv ranges both seem to output the same voltage.

Square wave also isn't 50% duty cycle, its fooked a bit...

BUT!

As I mentioned, I only wanted this for testing audio, so squarewave doesn't matter, and I really only ever needed the 2.5volt range anyway.

So, she'll be right!

[Andy Watson]

This is essentially the same as the Marconi TF 2103,. You could do worse than plagiarise the power supply from the Marconi manual.