I will try using grommets and see if that solves anything.
However discovered a REALLY weird phenomina... if I have the shorting plugs in, and i place my hand NEAR to either 7199 - NOT touching - the hum level increases. What th eheck is going on there?!? Is my ST70 turning into a theramin?!? Haha! Truly bizarre.
Burned fingers: nope the sockets cannot be grounded - they are of the type shown here:
http://www.dynakitparts.com/store/product.aspx?id=227
There is no ground tab - the underneath is the same as the top - just that bit of metal in the center...
Getting real tired of this bastard hum - taking all the enjoyment away from owning a ST70. Going back to basics again. All other posts I have made should be forgotten. Starting again here:
1) Dynaco ST70 unearthed, with RCA cheater plugs - low level hum. Not audible from normal listening distance.
2) Plug in my Quad 34 (or KingRex) pre-amp - hummmm! Unplug all inputs to the Quad 34. Nothing else plugged into the mains block. STILL hums. Disconnect Quad 34 earth - hums, but not QUITE as badly.
3) Plug in iPod directly to ST70 - as no.1, hardly any hum. Sounds fine.
4) Disconnect ground to Quad 34, PUT a ground on the St70 - hardly any hum.......
I have a migraine! Yellow_Light_Colorz_PDT_20
- John
P.S. I have the ST70 earth (when connected) attached to the mounting bolt of one of the mains trannies mounting bolts. Would it be better to try it at the star ground point near the quad cap?
Secondly, if I use rubber grommets under the transformer, I presume this now means it not as safe as it's isolated from chassis ground?...