"Upsizing the first filter cap can increase "B" voltage and add more loading to the transformer: Not a good idea in most cases."

Usually doing that is toughest on the vacuum tube rectifier. You may exceed the peak current the cathode can handle. Solid state rectifier diodes are more forgiving.

If you transformer is not getting hot with no load after running a few hours, you probably don't have a shorted turn on the heater winding. If the voltage of that heater winding is a little low, you could add a couple turns of new wire (it need not be physically adjacent to the heater winding), and connect that in series with the heater winding (you have to get the phasing right, measure the voltage. If it comes out lower, reverse the connections on the new wire.)

The first filter cap had been increased from 8 to 16μF (2x32 in parallel). I haven't got around to changing this back to 8μF yet. I was hoping that I could increase the HT current draw with a new voltage divider arrangement for the 6U7s & 6A8 screen supplies, but the HT did not drop significantly.

Something needs to be done with the HT because cathode to plate voltages push 300V in some cases (the plate voltage limit) and could go higher with extreme line voltage fluctuations which can go up over 255V on occasion (which cause my solar inverter to trip). Once I get the radio aligned after removing and replacing the tuning gang, I will see what effect the increased sensitivity has on stability. I will then have another go at the voltage divider, either to increase the total resistance in case of instability, or lower it if it is not unstable, since I have observed lower resistances seem to make the radio more unstable. Note that the voltage divider is not presently according to the original circuit, see the story of the radio in Special Projects. When all that is done I will look at the first filter cap and see if it should be reduced.

No less a guru then Neville Williams, a former editor of Electronics Australia, vale both, suggested in a letter in 1992 that a B+ of 265V would be in order. A resistance of 410ohm in between the cathode of the rectifier and the 1st filter cap drops B+ to 275V, about right, but if the line voltage drops away at night, the performance volume-wise suffers. So I would rather leave the higher B+ as is as long as cathode to plate voltages don't exceed don't exceed 300V the limit for the valves, especially as this is how the radio came to me.

I have thought of adding turns to the 6.3V filament winding of the mains tranny but I will keep this until the restoration is about complete to give the transformer every chance to give a sign that its is faulty, eg sudden changes in volume caused by a poor connection buried in it somewhere. Johnny has indicated that a shorted turn in the high current filament winding would cause a melt-down, so the low filament voltage, if due to a fault must be due to a high resistance somewhere. I such a fault cleared itself after extra turns were added I would be left with potentially too high filament volts. If I think it is faulty will consider a rewind.

In the meantime other jobs have taken over, eg painting the kitchen, and the radio is presently on the work bench upended showing its innards with nothing much happening. Looking at reinstalling the tuning dial next.

Usually doing that is toughest on the vacuum tube rectifier. You may exceed the peak current the cathode can handle.

Yes. Comprehensive data sheets for rectifier tubes will specify the maximum value capacitor to be used.

"Comprehensive data sheets"

RCA data sheet indicates 40μF max, unless plate resistance is added to the valve.

My radio was not hum-prone before the increase to 16μF was made so no worries about going back to 8uF.

STC830, what do you mean by parallel? Usually when you parallel a capacitor the capacitance increases ie 2x 32 is 64 or do you mean in series?

Sorry I do mean series - made the same mistake in my Story.