Hi Folks.

I am repairing a Silvertone 1928. I notice that the tube (1B1) is used as a balast tube. Can anyone tell me why a tube is used in this way rather than a resistor or other cheaper way,

thanks.

Frank Goddard. Doncaster England.

Frank, My Silvertone model 1926 uses the same ballast and Radiodoc informed me when I was restoring it that it was used to regulate the 3.2v dry cell batteries down to 2 volts for operation. Mine was missing and as long as I supplied 2.o v. I could just jump the pins. The 1B1 is rated @ 1.0v., .36amp., 2.8 ohms. I later found a 1B1 have used it both ways without any problems.
Hope this helps,
Jon.

Frank:
The reason they used a ballast tube instead of a resistor: the tube filament is made of a metal whose resistance changes with temperature. When the battery is new, the tube filament is warmer and has a higher resistance. As the battery discharges, the filament runs cooler, the resistance is lower, and the current stays about the same. As Jon said, get a steady source of two Volts, and you will not have to compensate for the battery discharging. Jumper the ballast tube, and listen.
Lewis
Lewis

Thank you both. This is great information. When running up the LT I used a 2 volt supply.No wonder the filaments were running low. Perhaps this could explain the very low volume levels too. Anyhow. I am still way off with the repair but now I don't have to look for problems that don't exist. Thanks again. Frank

One last question. What was the year of manufacture for the Model 1928.Thanks again,

Frank