[joebog1]

A little further progress has been made! See photo.

Below is a copy of an email Andy, (Diabolical_Artificer)and I have been having.
It explains the basics of my layout for the power supply involved.
As always, I stand ready to be shot down for bad design/new ideas/ different views. and general comment.

So the crop circles are the power transformer positions, i.e. two toroids.
The big holes are for two by F&T dual 100 uF @ 500 volt capacitors.
Square layout of four small holes and two large holes are for HT chokes.
Its all dual mono
Back panel outside ends are for two standard circular connectors for the umbilicals to the main amp unit.
Im still humming and haring about wheather to put bias regulator bottles on the power supply chassis or the main amp chassis hhmm hmm ....
Bias is supplied by two el cheapo 240 volt to 18 volt power transformers from China.
They run backwards of course, being fed by a separate 12 volt supply into the 18 volt secondaries, and I obtain about 160 volts or so from the primaries
as I need feed a 105 volt OB2. Thats then fed to the driver and output stages. ( DC coupled) via a 10K pot.
There are also two bias supplies.
Heaters are supplied by 12.6 volt winding on the mains toroids. One for each channel.
So back to the circular connectors. They carry HT, main earth , which is also return for the HT supply. bias, either AC 12 volts to feed the transformers in the main amp chassis,
or negative 105 volts to the bias control pots, and 12.6 volts heater supply.
Connectors are 7 pin and are laid out in two pins, three pins and two pins.
I figure the 3 centre pins to be ground ( and something of a screen) the two top pins to be heater supply with the remaining two pins to be bias, OR 12 volts to feed the bias transformers.
Putting 425-450 volts on one pin and minus 105 volts on adjacent pin strikes me as a bit stoopid!!, as the connectors are rated 500 volts and 5 amps per pin, BUT I imagine that they mean
generally NOT to push the insulation to breakdown point.

The several 3mm small holes on the back panel hold a BIG 2HP rated ( for inductive loads) contactor rated 25 amps at 250 volts, with a cosine of .4
and the remaining holes are for the 24 volts inrush limiter relay.


The four holes on top level of back panel are for input and output fuses for the HT supplies, and the large square hole is for a fused IEC connector for mains supply.
The outside will be painted 50% flat black, and the inside will be very light gray matt, so this old fart can read resistor colours.
The bottom panel is yet to be made, but is 1.6mm punched steel as well as the chassis, which is called "zincalum" in australia. Its zinc and aluminium electroplated onto the steel surface
and is bullet proof, rust and corrosion wise.
Topping it off on the bottom will be four 1" rubber door stops screwed onto the base as feet.

Its a standard construction technique of mine. All internal wiring will be laced with British Admiralty waxed linen thread from WWII.
Any other holes I may require for tagstrips or terminals will be drilled as needed with a hand drill.

I dont know if you play with power toroids, but the reason for my crop circles, ESPECIALLY on the inside of the torus, is for cooling air!!
The top washer that holds the whole kit and kaboodle down is drilled with matching holes, as are the neoprene washers underneath the traffo,
and underneath the hold down washer. In fact I make a LARGE hole in the centre of the neoprene washer underneath the transfomer,
that insulates the transformer from the chassis, but doesnt block the vent holes. Why the big rave ? your toroid will be AT LEAST 20 degrees cooler.
Ohh!!! and I never buy or make toroids with a cast in resin centre for single bolt hold downs, for exactly the above reason.

Another update when I proceed some.

Regards
Joe