Yesterday I spent almost the whole day doing a little fitting of my lastest amp chassis to its box and this necessitated one or two changes to things so they fit better. One of them was changing the old fashioned 50uf + 50uf cap from hanging off the botton, next to the output tube, to being mounted on the top of the chassis with the transformers. The reason for this is that I read the Valve Wizards grounding tale and realised I needed to isolate the grounds on the twin caps from the place I was originally going to put them. The basic reasoning being that those old twin caps are fitted into a hole and the earth lugs bent over to make both the connection to ground and the mechanical mounting of the part.
This was all well and good in the old days but we’ve moved on since then and what would have been a chassis earth to the highest current point, resulting in noise in the higher impedance circuits, is now floating and so I can take the earth connection to any point I want.
Simple in theory but I had to then figure out how to make the machanical connection but have it isolated from the chassis but still have it close to the original point of entry so the resistors and caps around it could still span the distance. So what I did was cut out a bush in copper clad circuit board so I could solder the ground lugs to a bush then cut out an aluminium mounting plate to that so the mounting could be made. I should have photographed it because after about three hours cutting, filling and fitting it was made and I was quite proud of my efforts even though the world may never ever see it… unless, the poor bugger, years down the track who ends up owning this thing takes it into his head to break it down to do some mod or other and sees how much work I put into cramming all this stuff into such a small space… and expected it to work!
Towrds the centre of the chassis and just above the speaker magnet you can see one of the ground lugs of the aforementioned 50uf + 50uf caps. Just to the left is one of the three bolts that holds it in and around the lug you can just see the cutout in the chassis to make it available to soldering to. I’ll take another photo soon without the circuit board and with all the stuff soldered up in and around that left end of the board… oh, its going to be tight!