![[-]](https://theultimatetone.com/images/collapse.png "[-]")
06-14-2024, 10:19 AM
Hi Guys
The 10R-10W is simply for current limiting into the filter caps.
Capacitively-coupled bias supplies are the poor/cheap/lazy man's way of making a negative rail without a proper winding available on the PT. In most cases, the coupling cap is under-value and the voltage rating is wrong - also too low. Such supplies are generally too low a voltage to provide proper control of the tubes particularly when the main plate supply uses the same winding with a full bridge.
Intuitively it seems like a worse proposition when the winding for a voltage doubled plate supply is used. But... in each case, the circuit would be impressively referred to as a "charge pump", which can be constructed in a reliable manner, but doing so makes the economics of it less impressive compared to adding an auxiliary PT given the small size of the latter.
For your interest: Doing the charge pump bias supply closer to correct requires using only polypropylene for the plastic coupling cap AND making sure the cap is properly rated to withstand the winding voltage. You may find that a 440VAC safety cap will suffice, and these are available up to 10uF.
Have fun
The 10R-10W is simply for current limiting into the filter caps.
Capacitively-coupled bias supplies are the poor/cheap/lazy man's way of making a negative rail without a proper winding available on the PT. In most cases, the coupling cap is under-value and the voltage rating is wrong - also too low. Such supplies are generally too low a voltage to provide proper control of the tubes particularly when the main plate supply uses the same winding with a full bridge.
Intuitively it seems like a worse proposition when the winding for a voltage doubled plate supply is used. But... in each case, the circuit would be impressively referred to as a "charge pump", which can be constructed in a reliable manner, but doing so makes the economics of it less impressive compared to adding an auxiliary PT given the small size of the latter.
For your interest: Doing the charge pump bias supply closer to correct requires using only polypropylene for the plastic coupling cap AND making sure the cap is properly rated to withstand the winding voltage. You may find that a 440VAC safety cap will suffice, and these are available up to 10uF.
Have fun
