I started troubleshooting my S-6 head, using a 7S11/7T11 pair with extender for the S-6.
Symptoms are: large negative offset, exaggerated amplitude and waveform horribly distorted at any frequency.
Rotating the trims have negligible effect (just to exclude some wiper's contact problem).
I start to check the biasing circuit (U20A/B) and the series resistors between +50 and -50V but I discovered that the schematic and the pcb layout does not coincide with the documentation I have.
The A-4 preamp board is marked 670-1402-01; the strobe board is marked 670-1403-03. The S/N marked on the housing is B044657.
Anyone have an updated scheme?
Moreover, I noticed that on the schematic there are are two distinct grounds. But i don't know how the JFET may work if the gate is referenced to one ground (the one with the triangular shape) and its drain is connected to U20D that use the ground coming from the power supply interface..
Any ideas? I'm a little puzzled.