05-14-2012, 12:42 PM
RE the speaker and output transformer:
1. One leg of the speaker secondary is connected to a small out of phase winding to oppose hum induced by the field coil before going to the voice coil. Sometimes the connections to the transformer or field coil go bad at the connecting wires, so carefully disassemble and confirm that you have an open. Now disconnect one leg of the voice coil and measure it and the transformer secondary. If the voice coil and field coil are both good, and the speaker is otherwise in good shape you only need the output transformer, which should not be hard to find. You don't have to have an exact duplicate, plus or minus 15% will not be audible. If you are going to change out the speaker, then you will have more considerations. Lots of options.
2. Many old schematics use M as indicator of 1000 as multiplier for resistors and meg as multiplier for 1000000, same as K in newer schematics What's worse is the newer schematics use M as 1000000 as multiplier. Well you can usually tell if the value makes sense, and if there is a parts list the value is many times clarified.
Good luck with your project.
1. One leg of the speaker secondary is connected to a small out of phase winding to oppose hum induced by the field coil before going to the voice coil. Sometimes the connections to the transformer or field coil go bad at the connecting wires, so carefully disassemble and confirm that you have an open. Now disconnect one leg of the voice coil and measure it and the transformer secondary. If the voice coil and field coil are both good, and the speaker is otherwise in good shape you only need the output transformer, which should not be hard to find. You don't have to have an exact duplicate, plus or minus 15% will not be audible. If you are going to change out the speaker, then you will have more considerations. Lots of options.
2. Many old schematics use M as indicator of 1000 as multiplier for resistors and meg as multiplier for 1000000, same as K in newer schematics What's worse is the newer schematics use M as 1000000 as multiplier. Well you can usually tell if the value makes sense, and if there is a parts list the value is many times clarified.
Good luck with your project.
