22-07-2015, 02:06 AM
Reservoir capacitor earthing did not even cure it as I planned so the battle went on.
Next thing was to put the scope on all the different stages of decoupling and I spotted matching hum on one of the rails.
I tried another smoothing capacitor on the end of R21 and this created a slight improvement in the amount of hum but not enough for it to be a solution. Next I tried removing the link carrying the power to R7 and R12 from R21 and added a 1k5 resistor and the extra smoothing capacitor and got a much better improvement.
After a bit of experimenting I selected 820R and 47uf for the extra smoothing and not the 33uf I tried to start with. This was done to keep plenty of voltage on the phase splitter to prevent it clipping.
It has got rid of the 100hz ripple and left a much smaller amount of 50hz.
Tomorrow when I turn the chassis back over having finished the underside works I will again try the alternate valve and adapter and see if the last few milivolts of 50hz goes as well.
I will try the other identical chassis without the reservoir earth mod and see what the R-C mod alone does. The original as found wiring is with the ground for the smoothing connected to the wire leading to the reservoir ground from the 0V on the mains transformer so it is not good so this first chassis is going to stay as it is now with the earth mod done even if it makes no difference on the other one.
I will update the circuit diagram in a few days and see if I can get a full snap shot of the diagram without all those little quirks from the CAD software not being compatible with my screen grabber.
Next thing was to put the scope on all the different stages of decoupling and I spotted matching hum on one of the rails.
I tried another smoothing capacitor on the end of R21 and this created a slight improvement in the amount of hum but not enough for it to be a solution. Next I tried removing the link carrying the power to R7 and R12 from R21 and added a 1k5 resistor and the extra smoothing capacitor and got a much better improvement.
After a bit of experimenting I selected 820R and 47uf for the extra smoothing and not the 33uf I tried to start with. This was done to keep plenty of voltage on the phase splitter to prevent it clipping.
It has got rid of the 100hz ripple and left a much smaller amount of 50hz.
Tomorrow when I turn the chassis back over having finished the underside works I will again try the alternate valve and adapter and see if the last few milivolts of 50hz goes as well.
I will try the other identical chassis without the reservoir earth mod and see what the R-C mod alone does. The original as found wiring is with the ground for the smoothing connected to the wire leading to the reservoir ground from the 0V on the mains transformer so it is not good so this first chassis is going to stay as it is now with the earth mod done even if it makes no difference on the other one.
I will update the circuit diagram in a few days and see if I can get a full snap shot of the diagram without all those little quirks from the CAD software not being compatible with my screen grabber.
