Traynor YBA-1 Help

[SSummer]

I am a newbie to amp work and got a Traynor YBA-1 1971
I took out the polarity switch since there was already a grounded power cord. There was a .05 620v cap grounding the switch and I'm not sure if that had anything to do with it but now I have loud hum. Was that lowering plate voltage? If I ground the treble pot ground to the chasis with a jumper, the noise in the low range goes away but I still have higher pitched noise/ hum.
What could be the cause of this and how can I solve it?

The other mod I did was add a .68 cap along with the 820 ohm resistor for V2 Cathode to ground like Marshall.(Mid Boost)
Now when I turn up my volume past 6 I get a high pitched squeal. Again what could be causing this? Could it be the same grounding/noise issue?

Help please

[danman]

We will need some pics of the power cord wiring to be sure that it is right. Pics of the whole board with socket wiring and tonestack wiring would help too. Do you have the hot wire (black) from the power cord connected to the fuse and then on to the power switch? Marshall did it wrong years ago and fused the neutral (white) wire instead of the black like it is done now. Did you attach the green (ground) wire from the cord to a sturdy grounding point inside the amp? The squeal you are hearing may likely be oscillation caused by the extra gain that the mid boost cap is providing. Cleaning up the lead dress around the sockets will usually cure this. It is also possible that you moved one of the wires accidentally and now the amp is going into oscillation. Full pics of everything will help us to diagnose but you will need to host the pics on an image sight as the new forum setup will not allow direct posting.