01-26-2026, 10:45 AM
Hi SlidesK,
Sounds like you are making good progress.
Most resistors in these sets are half watt. the old carbon resistors look bigger than the newer metal film ones. The only place where you might need a 1 watt resistor is the cathode resistor for the 50L6.
Re the 120V B+, this may be due to low current draw. if there was no current draw on B+ due to a wiring issue, a bad output tube or a bad cathode resistor for that output tube, the B+ will be higher. It could be as high as 140V if no current was drawn.
Did you measure 120V at the cathode of the rectifier? Measure on the other side of the field coil, at the junction of the speaker field, 20 uF cap, Output transformer, etc. If much less than 83V, then you may have an incorrect speaker or there is a problem with the field coil. However, field coils either short, causing a low resistance or open causing infinite resistance.
The biggest draw on the power supply is the output tube. The output tube in these sets is bias for "Class A", where the current is rather constant between minimum volume and maximum volume. For a 50L6 at 100V, the plate current at minimum power output is 49mA. At maximum output, it is 50mA. The diagram calls for a 130 Ohm resistor.
A resistor is good if it is within 20% of specified value. If "pregnant" or cracked, then change it out even if the reading is good.
Sounds like you are making good progress.
Most resistors in these sets are half watt. the old carbon resistors look bigger than the newer metal film ones. The only place where you might need a 1 watt resistor is the cathode resistor for the 50L6.
Re the 120V B+, this may be due to low current draw. if there was no current draw on B+ due to a wiring issue, a bad output tube or a bad cathode resistor for that output tube, the B+ will be higher. It could be as high as 140V if no current was drawn.
Did you measure 120V at the cathode of the rectifier? Measure on the other side of the field coil, at the junction of the speaker field, 20 uF cap, Output transformer, etc. If much less than 83V, then you may have an incorrect speaker or there is a problem with the field coil. However, field coils either short, causing a low resistance or open causing infinite resistance.
The biggest draw on the power supply is the output tube. The output tube in these sets is bias for "Class A", where the current is rather constant between minimum volume and maximum volume. For a 50L6 at 100V, the plate current at minimum power output is 49mA. At maximum output, it is 50mA. The diagram calls for a 130 Ohm resistor.
A resistor is good if it is within 20% of specified value. If "pregnant" or cracked, then change it out even if the reading is good.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
Best Regards,
MrFixr55




