11-07-2019, 03:40 PM
You will need to know exactly what model Freshman you have. Some are with "C" battery, some without.
"Most" schematics for the Freshmen can be found online. Download and review if it is correct for your radio.
The schematic will identify the "C" voltage required. Sometimes a radio will use two "C" voltage, usually because of the last audio tube type.
Generally, if all the tubes are '01a then the "B" voltage will be 67-1/2 for no "C" battery. For "B" voltage of 90 volts a "C" battery will be 4-1/2 volts.
You will need to know what tube is used for the last audio stage to get it correct... A 112 or a 171a will need both a higher "C" and "B" voltage.
If you are using '99 tubes and socket adapters the "A" voltage will be 4-1/2 volts.
Without any "C" battery connected the radio may play for a moment and stop. If the "C-" is connected to A+B- connection essentially jumping out the "C" circuit, the radio will play with a maximum of 67-1/2 "B", no more.
The purpose of the "C" battery is to provide negative potential for the grid(s) of the tubes. If the grid in the tube is not negative enough it will draw excessive plate current and soon exhaust the thorium on the filament. The tube becomes "paralyzed" and will have to be rejuvenated. The tube can only be rejuvenated a few times then all the thorium is gone. The emission of electrons goes to zero. Yes a radio will play loud and distorted without "C".
A "C" battery does not provide current, just potential so most any cell(s) can be used. But, your power supply does have a "C" output...
Also, set the power supply "A" voltage that lights the filaments if you are using '01as to 6 to 6.6 volts. Do not set it for 5 volts, the rheostats provide not only volume, but lower the voltage and provide a small amount of bias as well.
Do not use 1 amp 01 tubes in this radio, they may cause the filament rheostat to burn up and may overload your power supply...
GL
Chas
"Most" schematics for the Freshmen can be found online. Download and review if it is correct for your radio.
The schematic will identify the "C" voltage required. Sometimes a radio will use two "C" voltage, usually because of the last audio tube type.
Generally, if all the tubes are '01a then the "B" voltage will be 67-1/2 for no "C" battery. For "B" voltage of 90 volts a "C" battery will be 4-1/2 volts.
You will need to know what tube is used for the last audio stage to get it correct... A 112 or a 171a will need both a higher "C" and "B" voltage.
If you are using '99 tubes and socket adapters the "A" voltage will be 4-1/2 volts.
Without any "C" battery connected the radio may play for a moment and stop. If the "C-" is connected to A+B- connection essentially jumping out the "C" circuit, the radio will play with a maximum of 67-1/2 "B", no more.
The purpose of the "C" battery is to provide negative potential for the grid(s) of the tubes. If the grid in the tube is not negative enough it will draw excessive plate current and soon exhaust the thorium on the filament. The tube becomes "paralyzed" and will have to be rejuvenated. The tube can only be rejuvenated a few times then all the thorium is gone. The emission of electrons goes to zero. Yes a radio will play loud and distorted without "C".
A "C" battery does not provide current, just potential so most any cell(s) can be used. But, your power supply does have a "C" output...
Also, set the power supply "A" voltage that lights the filaments if you are using '01as to 6 to 6.6 volts. Do not set it for 5 volts, the rheostats provide not only volume, but lower the voltage and provide a small amount of bias as well.
Do not use 1 amp 01 tubes in this radio, they may cause the filament rheostat to burn up and may overload your power supply...
GL
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
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