[Reece]

Half-wave rectifiers will exhibit 60Hz hum; full waves, 120Hz. Hum pickup from other sources in the radio, especially around the audio section, will be 60Hz. Sometimes lead dress has to be changed, getting sensitive audio wires tight against the chassis and away from AC lines. Sometimes replacing such longer lines with shielded cable, shield grounded, will help. First audio tubes often need to be shielded or should be a metal tube with pin 1 grounded, if an octal. Best to replace power supply filters with the same as spec'd. If adding capacitance to try to reduce hum, don't add it to the first cap right at the rectifier, but add it after the speaker field or the power supply resistor (assuming a capacitor input filter.) Adding too large a cap at the rectifier can look like a short to the tube on startup.