Tube question from a rookie

[Electronic M]

Originally Posted by Wind157

I had someone else say B+ also (not sure what that is). There is a rectangular resistor near the rectifiers that I suspect is bad. Multimeter and resistance test don't give consistent results and there is corrosion on it's lead that seems to be coming from the resistor itself and no other components have any corrosion/oxidation at all. Waiting on a new one to confirm my theory.

B+ is a/the main power supply voltage for the set. Some sets have more than one B+ rail (each will have different voltage normally) either divided off the highest voltage rail by a resistor or supplied by a separate rectifier. Typical voltage in tube sets is somewhere between 67 and 1000V (depending on the category of device).

The origin of the term dates from the first tube radios in the 1910's and 1920's...Until the late 20's there was no practical way to filter rectified AC to be clean enough to NOT swamp out RF/audio with AC powerline hum in radios, thus all radios ran on batteries...Back then the "A" battery ran the tube heaters/filaments, and "B" ran the plates...There was sometimes also "C" for the grid bias, but modern resistor dividers from the B supply eliminated the need for "C".