Gould J3B signal generator repair help

I had another crack at this, cleaning the board and starting from fresh after getting thoroughly sick of it... :D

I have discovered that the parasitic oscillations seemed to be caused by running the pcb with various extension wires in order to test out of the chassis.

This is slightly embarrassing, in that it was in fact fixed when i described it as "sort of fixed" but just needed neat wiring and the shields back in place.


It works and calibrates fine now except for the fact that the lowest frequencies take a long time to settle.

Rapidly rotating the dial on the 10-100Hz scale results in bouncing back and forth between 4-12v Pk-Pk, against a nominal 8V, and takes something like 30 seconds to settle down on the lower end.

The transistors and diodes test ok with a multimeter and the electrolytic caps are all fresh, any idea or should i try a shotgun semiconductor replacement?

The output from the wein bridge section still clips hard during start up, as shown in the pictures in post 19 of this thread, playing with r34 doesnt replicate it in steady state as suggested by BSST above.

Thanks all for your help.
 
I'd advise simply ignoring power-on behavior, as DC bias time constants are aggravating settling time.

Rapidly rotating the dial on the 10-100Hz scale results in bouncing back and forth between 4-12v Pk-Pk, against a nominal 8V, and takes something like 30 seconds to settle down on the lower end.

If the amplitude bouncing looks sinusoidal without clipping or spurious glitches, then I think you'd see little change in these phenomena with new semiconductors or opamps, IMO. Rather, the amplitude bouncing is interaction of the thermistor's thermal time constant with the low generator frequency. You might see improvement of oscillator residual THD at higher frequencies with modern opamps, but this is by no means assured. Of course, distortion in the output buffer is also a possibility. I suggest THD measurement of both oscillator and output stages for comparison to help decide any subsequent rehab.

Good work!

Steve