R20 is a filament dropping resistor. It's in series with two tubes across the AC line. One 35 volts and the other 50 volts for a total of 85 volts. If your AC line is 125 the resistor needs to drop 40 volts @ 150 ma. You should use a wire wound resistor 250 to 275 ohms @ 10 watts or greater. It will be hot in operation.
Norm
:Hope someone can help! I have the Riders schematic for
: this but no value and wattage is given for R20 which
:is bad in this one. Someone previously has put in 2
: resistors in series to try and fix the problem. The
:original is connected between the heaters of the 50B5
:and 35W4 tubes and am guessing this resistor was put
: in to get rid of excessive heat when using AC power.
: Right now the radio works but the chassis on that
:side around the original resistor which is mounted in
: an aluminum container on top of the chassis gets hot
: enough to fry an egg on so the repair job did not
:work. Need to know what the original resistance and
: wattage of the original resistor was. It is about 4"
: long by 1/2" wide with solder joints at each end
:(it is not tapped anywhere. Thanks-Ken
Thank you for the info you sure are quick! I have only been interested in these old pieces of history for about 3 years so have a lot to learn! Did you know this or had to look it up? Ken
It's easy to figure. Tubes draw .15 amps. Since tubes filaments add up to 85 volts you need to drop another 40 volts. To determine resistance divide current into voltage. 40 divided by .15 = 267. So a resistor around this value will work.
Wattage is determined by voltage times current. Voltage is 40 times .15 = 6 watts. Always use a wattage higher than needed so that means 10 or greater.
Norm
::Hi Ken
::
:: R20 is a filament dropping resistor. It's in series with two tubes across the AC line. One 35 volts and the other 50 volts for a total of 85 volts. If your AC line is 125 the resistor needs to drop 40 volts @ 150 ma. You should use a wire wound resistor 250 to 275 ohms @ 10 watts or greater. It will be hot in operation.
::
::Norm
::
:::Hope someone can help! I have the Riders schematic for
::: this but no value and wattage is given for R20 which
:::is bad in this one. Someone previously has put in 2
::: resistors in series to try and fix the problem. The
:::original is connected between the heaters of the 50B5
:::and 35W4 tubes and am guessing this resistor was put
::: in to get rid of excessive heat when using AC power.
::: Right now the radio works but the chassis on that
:::side around the original resistor which is mounted in
::: an aluminum container on top of the chassis gets hot
::: enough to fry an egg on so the repair job did not
:::work. Need to know what the original resistance and
::: wattage of the original resistor was. It is about 4"
::: long by 1/2" wide with solder joints at each end
:::(it is not tapped anywhere. Thanks-Ken
:
:Thank you for the info you sure are quick! I have only been interested in these old pieces of history for about 3 years so have a lot to learn! Did you know this or had to look it up? Ken