As I have mentioned I am designing a 6AU6 based mic preamp. Thanks to
Patrick et al I now have hum free HT rails. However, I still find some
50Hz hum and 10mS period PSU spikes in the output. By shorting the grid
of the first stage these both disappear so that is where they are
getting in. By turning off the HT they also both disappear so it seems
the source is the PSU. So the question is what should I do to stop it. I
tried grounding the mains transformer metal clamp and this helped a bit
but there is no connection of this transformer for a screen of any kind.
I am also using fast recovery diodes in the HT supply because I have
read they produce less spike interference. Any help appreciated.

For a not very good picture of the waveform at the preamp output look he

http://s103.photobucket.com/albums/m...6CFopnoise.jpg

Cheers

Ian