Your 75 filament is in series with other 6 volt tubes in this radio. However cathode of both 48 tubes are connected to one side of the filament. A short between cathode and filament will cause the 75 to burn out.
Can you test the 48's for cathode/filament short? If not pull the 48's and see if your 75 is still bright?
http://www.nostalgiaair.org/PagesByModel/116/M0007116.pdf
Norm
:Hello out there! I need some help. I have a Coronado 6953 tombstone 32 volt DC radio. The radio uses two #48 tubes, one each #76, #75, #6A7, and a #6D6. The problem I have is that when I hookup my 32 volt power supply (regulated at that, the #75 glows real bright, and eventually fries. I have tried various power supplies, same thing. When you look at the schematic (you can refer to it on this site, (Gamble-Skogmo 6953), it appers the #75 is hooked up in parallel to the 32v source, though not 100 percent sure. Anyone out there have any ideas, or experience with these radios? Any help appreciated!- Rob
The 48 Tubes have 30V heaters
The 6A7, 75, 76, and 6D6 have 6.3V heaters.
I traced the circuit, and found a possible reason for your problems. The 48 Tubes should be wired in parallel, and should be in series with a small dropping resistor (shown at the bottom). The other tubes should be wired in SERIES, and also be series with the larger dropping resistor. If the 75 is in parallel with the 32V line, chances are that is why it is glowing too bright and burning out, and you have a wiring fault. Also check if the right tubes are in the correct locations. It is also possible that a tube with the wrong current rating was incorrectly substituted in that series string. It is possible that the large dropping resistor may have shorted as well.
:Hi Robert
:
: Your 75 filament is in series with other 6 volt tubes in this radio. However cathode of both 48 tubes are connected to one side of the filament. A short between cathode and filament will cause the 75 to burn out.
:
: Can you test the 48's for cathode/filament short? If not pull the 48's and see if your 75 is still bright?
:
:http://www.nostalgiaair.org/PagesByModel/116/M0007116.pdf
:
:Norm
:
::Hello out there! I need some help. I have a Coronado 6953 tombstone 32 volt DC radio. The radio uses two #48 tubes, one each #76, #75, #6A7, and a #6D6. The problem I have is that when I hookup my 32 volt power supply (regulated at that, the #75 glows real bright, and eventually fries. I have tried various power supplies, same thing. When you look at the schematic (you can refer to it on this site, (Gamble-Skogmo 6953), it appers the #75 is hooked up in parallel to the 32v source, though not 100 percent sure. Anyone out there have any ideas, or experience with these radios? Any help appreciated!- Rob
:I looked at the circuit and did some research for you:
:
:The 48 Tubes have 30V heaters
:
:The 6A7, 75, 76, and 6D6 have 6.3V heaters.
:
:I traced the circuit, and found a possible reason for your problems. The 48 Tubes should be wired in parallel, and should be in series with a small dropping resistor (shown at the bottom). The other tubes should be wired in SERIES, and also be series with the larger dropping resistor. If the 75 is in parallel with the 32V line, chances are that is why it is glowing too bright and burning out, and you have a wiring fault. Also check if the right tubes are in the correct locations. It is also possible that a tube with the wrong current rating was incorrectly substituted in that series string. It is possible that the large dropping resistor may have shorted as well.
:
::Hi Robert
::
:: Your 75 filament is in series with other 6 volt tubes in this radio. However cathode of both 48 tubes are connected to one side of the filament. A short between cathode and filament will cause the 75 to burn out.
::
:: Can you test the 48's for cathode/filament short? If not pull the 48's and see if your 75 is still bright?
::
::http://www.nostalgiaair.org/PagesByModel/116/M0007116.pdf
::
::Norm
::
:::Hello out there! I need some help. I have a Coronado 6953 tombstone 32 volt DC radio. The radio uses two #48 tubes, one each #76, #75, #6A7, and a #6D6. The problem I have is that when I hookup my 32 volt power supply (regulated at that, the #75 glows real bright, and eventually fries. I have tried various power supplies, same thing. When you look at the schematic (you can refer to it on this site, (Gamble-Skogmo 6953), it appers the #75 is hooked up in parallel to the 32v source, though not 100 percent sure. Anyone out there have any ideas, or experience with these radios? Any help appreciated!- Rob