Selenium rectifiers increased their internal resistance with age and use. This was accompanied by commensurate voltage drop rendering less output voltage for use as B+. The suggestion of using a silicon diode replacement is a good one. I would recommend that you add a 22 ohm 1 watt resistor in series with the silicon diode AND place a .001 mfd 1KV capacitor in parallel with the new silicon diode. This addition will serve to reduce surges through the diode junction and to bypass transients around the diode. I have followed this practice for many years and found it to be beneficial. Good luck. Dr. T.