06-16-2012, 10:20 AM
Hello to all,
Working on the next project, a 40-150. Recapped fully, replaced all out of spec resistors, ohmed out the power and output transformers and voice coil, all good. Went to fire it up, no output (ie reception or static) and one of the 41 output tubes overheated. Although I had replaced the coupling cap (#52), I do not have the ability to check for leakage, so I re-replaced with a new cap. #46 to the 7C6 was also replaced.
Pulled the 41s, put in the rectifier tube and went to check voltages. Measure 330V across the 12 mfd electrolytic (#61) as opposed to 270V, and I understand that the new meters do not load a circuit to the degree that the old VTVMs did. Checked across the 16mfd electrolytic and read 286V as opposed to 185V and plate voltages at the 41s was 288V as opposed to 180V. Now, I would presume that the voltages would be higher due to the fact that there is no load, but does this high a voltage seems out of the ordinary?
Wanted to get opinions prior to the next phase of troubleshooting as I really don't want to fry a 41 while I am checking the voltages with the tubes in place. Have already checked all connections I reworked in replacing components against the schematic and my work checks out, so no incorrect connections or cold solder joints.
Thanks for any assistance you may render.
Richard
Schematic here:http://www.nostalgiaair.org/Resources/331/M0013331.htm
Working on the next project, a 40-150. Recapped fully, replaced all out of spec resistors, ohmed out the power and output transformers and voice coil, all good. Went to fire it up, no output (ie reception or static) and one of the 41 output tubes overheated. Although I had replaced the coupling cap (#52), I do not have the ability to check for leakage, so I re-replaced with a new cap. #46 to the 7C6 was also replaced.
Pulled the 41s, put in the rectifier tube and went to check voltages. Measure 330V across the 12 mfd electrolytic (#61) as opposed to 270V, and I understand that the new meters do not load a circuit to the degree that the old VTVMs did. Checked across the 16mfd electrolytic and read 286V as opposed to 185V and plate voltages at the 41s was 288V as opposed to 180V. Now, I would presume that the voltages would be higher due to the fact that there is no load, but does this high a voltage seems out of the ordinary?
Wanted to get opinions prior to the next phase of troubleshooting as I really don't want to fry a 41 while I am checking the voltages with the tubes in place. Have already checked all connections I reworked in replacing components against the schematic and my work checks out, so no incorrect connections or cold solder joints.
Thanks for any assistance you may render.
Richard
Schematic here:http://www.nostalgiaair.org/Resources/331/M0013331.htm
Richard
