[Milsurplus] Low B+: The Genius of A.R.C.

[Ray Fantini]

Not being critical because I have not done the work myself and have no experience using octal remote cutoff pentodes at low voltages but have to wonder why other then the convenience of having 24 or 28 volts there why you use such a low voltage?  Looking at the plate characteristics curves of the 12SK7 the tube appears to perform rather poorly below 40 to 50 volts and almost at the point of having no plate current at 20 volts. At 60 volts the tubes plate characteristics appear fairly uniform out to above 250 volts. Not that I have run any radios at that low a percentage of applied voltage I do operate most of the older tube radios I have at 80 to 90 % of design voltage, and looking at plate curves can see where you can get away with operating at 30% or around 75 volts on the plate of a radio designed for 250 but 24 volts would be on the verge of no plate current at all. 
I also wonder about the magnetic fields, being that IF coils are designed and spaced with an assumption of a given plate current and voltage that produced a given magnetic field and you are using only a fraction of the voltage and current wont the field be weaker? Would have thought that this may provide week coupling between stages or an inability to drive the next stage at all. Please understand that I am not questioning your work, if you have done this and it works your word is good enough for me, but what I am questioning are things like the alleged "all solid state" BC-348 where someone takes a hand full of FET and replaces the tubes and says that's all that is needed along with a nine volt battery. I just cannot see low voltages and low currents performing well in circuits designed for use with voltages a factor of ten times higher especially with something like an oscillator developing enough feedback to begin osculation.
Soon, whenever my junk ARR-41 dyno deck shows up I am starting work on a solid state inverter that will take place of the stock dyno in the ARR-41 that I have. The ARR-41 requires 250 and regulated 150 and may try experimenting with running the radio around 175 to 180 volts on the 250 volt buss and see if that makes any difference in the receivers performance. The regulated voltage to the PTO will have to stay the same but figure a 30% reduction in B+ won't be an issue.