[patrick-turner]

Regarding the wien bridge oscilator.
I deleted the j-fet amplitube regulator. I could not sleep because it produced a huge amout of THD. But at least the Vo did not bounce, and all F between 1Hz and 1MHz had the same amplitude.

But after deleting the j-fet, I tried the ITT P564 thermistor and a an adjust pot to see just how well it worked. I soon saw how badly the darn thing worked with terrible V bounce. But THD was very low. But I could not get all the F in 100kHz to 1MHz range to oscillate. I tried lots of things and had to delete the bloomin thing.

Then I built a high input Z rectifier to produce a max +Vdc of +3Vdc. This is applied to a base of a common emitter stage which inverts the at the collector output so that a Vdc can be derived to power a BC640 bjt with Re 180r so that as it turns on it feeds collector current up to 22mA through 4 series lams each rated for 12V x 50mA.
Suitable R + electro Cs slow down any change in lamp DC current and its the DC though the lamps that causes the most change in their resistance, which varies between 27r cold to up 115r with about 22mA.

I have not tried my 3 bjt Vo regulator yet, but it does seem to behave far better than the j-fet, and up to a slightly higher Vo.

The ß just goes over 0.33 at 3.5Vrms input to my circuit.
But at turn on, ß = 0.1, so oscillations will be max and distorted until lamps warm up SLOWLY.

This NFB is a much lower resistance circuit so I expect no troubles getting all F between 100kHz and 1MHz

I should get far lower THD, because the VNFB produced has no visible THD on my CRO, unlike the j-fet which produced several % 2H.

I removed the PSU from inside the box, and re-built it much better at the rear of the back plate so I have to make a cover to screw over it. This re-arrangment gave me room to put the Vo regulator in a nice board against the inside of the rear panel. The arrangment keeps noise extremely low.

I will ammend the circuit at my website when I try the new Vo reg and iron out any unexpected bugs which always manage to accompany R&D when you get keen.

So, what did anyone else work on today? Or have you given up?

Patrick Turner.