11-10-2013, 01:17 AM
Time to check the resistance across your speaker field coil. That's the next thing in line for your B+ chain. If that's open, it will not allow power through to anything else in the set (filaments are a different winding on the transformer, so the tubes will light regardless).
If the field coil is open, you can bypass it temporarily with a 1000 ohm, 10 watt resistor for test purposes. Be aware, though, that your speaker will not perform as it should, since it will have no magnet for the voice coil to work against. Your volume will be extremely low and distorted.
Your 451 volts sounds pretty high, but it is likely due to not being under load. It should drop to about 250 volts once you have the rest of the radio connected to it.
You can get a voltage reading connecting your negative lead directly to chassis ground, but take note that the large can type resistor mounted to the chassis forms the circuit from the transformer to chassis ground (and creates the negative bias for some parts of the radio). Make sure this resistor is OK, should be about 180 ohms from one end to the other.
If the field coil is open, you can bypass it temporarily with a 1000 ohm, 10 watt resistor for test purposes. Be aware, though, that your speaker will not perform as it should, since it will have no magnet for the voice coil to work against. Your volume will be extremely low and distorted.
Your 451 volts sounds pretty high, but it is likely due to not being under load. It should drop to about 250 volts once you have the rest of the radio connected to it.
You can get a voltage reading connecting your negative lead directly to chassis ground, but take note that the large can type resistor mounted to the chassis forms the circuit from the transformer to chassis ground (and creates the negative bias for some parts of the radio). Make sure this resistor is OK, should be about 180 ohms from one end to the other.
