dave wrote:


Look on the bay for a Heath IG-58 (several variations). They are very
low distortion for the price. (Typically 0.04 to 0.02 % THD, depending
on level and frequency). You can get a guaranteed one for $125 or less.
Or wait for a bargain and grab one for $50.


** You meant a Heath IG-18 right?

Yeah - that looks pretty good, except for the lack of a decent frequency dial.

My generator has a 3inch aluminium disk that turns with the frequency pot, marked across 290 degrees, turned by a 6:1 reduction drive using ball bearings.

I also have a ancient, valve Wien Bridge generator that uses a large, dual tuning gang coupled to a 30:1 reduction worm drive - as you might imagine, frequency adjustment is very silky and resolution is genuinely infinite.

Lotsa bench generators use dual tuning gangs for frequency, cos they give ultra smooth, noise free adjustment that lasts for - unlike most dual pots.

But watch out if you try to float the internal circuitry and just leave the metal case safety grounded, it does not work. It is essential that that case and shielding around the tuning gang all be at the same potential or supply frequency leakage from the power transformer secondary injects straight into the oscillator and causes major amplitude modulation.

..... Phil