02-21-2009, 10:32 PM
Your B+ is running higher because of the 25 cycle pwr trans being used on 60 cycles mains. It would be best to replace the pwr trans if possible. Transformers do run hotter internally when applying 60 cycles into a 25 cycle because of the size of wires windings inside a 25hz type as compared to the 60hz types. If ac trans swap is out of the question, here are a couple things ( guaranteed) so you can bring down B+ voltage in your sets that have 25 cycle trans.
(1) find your power transformers center-tap wire that usually is soldered directly to chassis. Cut & lift it off chassis, install a 25 watt wirewound power resistor ( exact best ohms needed can be found by subbing in & out a few different values with jumper wires with alligator clips in "series" with trans CT back to chassis ground) while monitoring your B+ voltages, slow upping with your variac to modern line voltage. Ohms needed could be anywhere from 3-500 ohms in my guess. Monitoring your B+ while subbing in the resistors will yield you a good match.
or try this: ( may be easier)
(2) find the socket connection (wire) off your rectifier tube socket that feeds your radios 1st [ First] B+ filter cap according to schematic. Cut & lift the wire, add a 20 watt wirewound pwr resistor in "series" ( try subbing anywhere from 250- 350 ohms) using alligator clip jumpers while monitoring your B+ while slow upping your variac to work on modern line voltage. You will find a good match by subbing in various resistors until you get your B+ voltages near schematics ratings +/- 15%
* either of the above suggestions will drop your B+ voltage. Exact matching yield by experimental subbing the 20 watt w.w. resistors via 2 jumper wires with alligator clips on each ends.
*for those that say it is ok to run a 25hz power trans on 60hz mains needs to try this to be "convinced" sometimes via "audio"!
find a vintage German or Mexico 50 hz version of a vintage tape-deck. Plug it into 60hz mains & listen to it thru any amplifier. Distortion , lousy sound, are due to "higher B+" voltages courtesy of only 10hz difference upping the B+! Try it sometime, and the nay-sayers 25hz vs 60hz can be convinced easily "by ear"! Enjoy your vintage Radios!!
(1) find your power transformers center-tap wire that usually is soldered directly to chassis. Cut & lift it off chassis, install a 25 watt wirewound power resistor ( exact best ohms needed can be found by subbing in & out a few different values with jumper wires with alligator clips in "series" with trans CT back to chassis ground) while monitoring your B+ voltages, slow upping with your variac to modern line voltage. Ohms needed could be anywhere from 3-500 ohms in my guess. Monitoring your B+ while subbing in the resistors will yield you a good match.
or try this: ( may be easier)
(2) find the socket connection (wire) off your rectifier tube socket that feeds your radios 1st [ First] B+ filter cap according to schematic. Cut & lift the wire, add a 20 watt wirewound pwr resistor in "series" ( try subbing anywhere from 250- 350 ohms) using alligator clip jumpers while monitoring your B+ while slow upping your variac to work on modern line voltage. You will find a good match by subbing in various resistors until you get your B+ voltages near schematics ratings +/- 15%
* either of the above suggestions will drop your B+ voltage. Exact matching yield by experimental subbing the 20 watt w.w. resistors via 2 jumper wires with alligator clips on each ends.
*for those that say it is ok to run a 25hz power trans on 60hz mains needs to try this to be "convinced" sometimes via "audio"!
find a vintage German or Mexico 50 hz version of a vintage tape-deck. Plug it into 60hz mains & listen to it thru any amplifier. Distortion , lousy sound, are due to "higher B+" voltages courtesy of only 10hz difference upping the B+! Try it sometime, and the nay-sayers 25hz vs 60hz can be convinced easily "by ear"! Enjoy your vintage Radios!!
