Just a wild thought: The voltage drops across each quad cap section are due to the series "dividing" resistors which supply voltage to them.
Why not just increase those resistors a bit so that there is a little more voltage drop resulting in safe voltage levels at the cap (like in Olden Times.)
Might even have to add a new resistor for a drop before you get to the ATOM 600v cap which is "upstream" of the Quad Cap.
Any thoughts?
The resistor and cap work together as an RC filter, and the value of each contributes to how effective the filter is at shunting AC noise to ground. If you change one or the other, the characteristics of the filter change. Going to a larger resistor will drop the voltage at any nodes following the resistor, and changing to a larger cap will make the filter more effective, but doing each will change the time constant of that part of the circuit, slowing it down in its ability to supply the voltage the amp is demanding. Also if you look at the schematic for most of the Sunns, you will see that they use what is known as a choke input filter, where the choke is the first thing that is seen by the power supply after the standby switch. If you try to put a resistor between the choke and the power supply, the resistor would have to have a very large wattage rating because the whole amp's power supply has to go through this resistor. Also, any value of resistor sufficient to lower the voltage of the B+ to safe levels for the can cap would greatly increase the sag of the amp...not good for a bass amp. I don't think you would like it for a guitar amp either.
The first cap and the choke form an RL filter, and it is quite effective at reducing hum and noise. If you want to use a GZ34 rectifier tube this cap needs to be 60uF or less, and with today's lousy GZ34's, less is probably a wiser course of action for tube life. If you choose to use solid state rectification, then you can go larger than 60uF for this cap. I have used up to two 220uF caps in series for a 110uF value at this stage and it works and sounds good for bass amps.
The next cap after the choke and the following resistor are the first RC filter, and node A here supplies the power tubes with their B+. This node also supplies the screens of the power tubes since the amp is ultralinear. Node B supplies the phase inverter with it's voltage. Changing the 15k resistor to a larger value before this node would make any voltages following this resistor lower. The next node, node C supplies the preamp with its voltages. I have changed the 33k resistor before this node to a larger value in a later 200S to get it to react more like the earlier Dynaco transformer amps which have lower voltages overall, but specifically lower voltages in the preamp.
So long story short, adding a resistor between the rectifier and the choke isn't a good idea due to several things, but mainly sag and heat. You can change the other resistors in the supply but that won't affect the power tube plate or screen voltages, and won't make your voltage any lower for the can cap. So it is not a valid solution.
Greg
