02-04-2014, 02:53 PM
Once you get the sch,
(you are an electronics tech so I won't lecture you on basic safety, bad wires etc - just mind the high voltage, tubes get it very high)
1. Whatever rectifier you got, disconnect it.
Then plug the transformer in and watch if it is still heating up or stays cool.
Measure its voltages to at least be in the ballpark (the one to the rectifier - maybe 200V or something of the sort, filaments are probably 6.3V for the miniatures).
If it passes that, deal with the rectifier. If it is Selenium type, you will probably replace it with a diode bridge (you could use 1N4007 for this) and a resistor if needed.
2. if you are OK, start looking for a reason the transformer heated.
Inspect the wiring, look for load shorts from the rectifier.
If not obvious, go to recap.
3. I would not touch any caps other than the electrolytic ones. If they dried up, and you are not keen on restuffing them to keep the looks, simply cut them off (do not bypass), remove and replace with a modern type. If you want to keep some looks, leave them in fully cut off, still use the newer types instead. if you are more of a perfectionist, remove them, gut them, re-stuff with the modern type, seal back, solder in. In the rectifier section, especially for the one that is the first to filter the rectifier, Use good grade caps with as high a ripple current as possible. If needs be, you could parallel or serialize.
4. Test the tubes.
5. Put them in, connect the speaker.
6. Plug in, watch the transformer. if it is still not oozing the tar, proceed. if it is, well then we will deal with it. If possible.
(you are an electronics tech so I won't lecture you on basic safety, bad wires etc - just mind the high voltage, tubes get it very high)
1. Whatever rectifier you got, disconnect it.
Then plug the transformer in and watch if it is still heating up or stays cool.
Measure its voltages to at least be in the ballpark (the one to the rectifier - maybe 200V or something of the sort, filaments are probably 6.3V for the miniatures).
If it passes that, deal with the rectifier. If it is Selenium type, you will probably replace it with a diode bridge (you could use 1N4007 for this) and a resistor if needed.
2. if you are OK, start looking for a reason the transformer heated.
Inspect the wiring, look for load shorts from the rectifier.
If not obvious, go to recap.
3. I would not touch any caps other than the electrolytic ones. If they dried up, and you are not keen on restuffing them to keep the looks, simply cut them off (do not bypass), remove and replace with a modern type. If you want to keep some looks, leave them in fully cut off, still use the newer types instead. if you are more of a perfectionist, remove them, gut them, re-stuff with the modern type, seal back, solder in. In the rectifier section, especially for the one that is the first to filter the rectifier, Use good grade caps with as high a ripple current as possible. If needs be, you could parallel or serialize.
4. Test the tubes.
5. Put them in, connect the speaker.
6. Plug in, watch the transformer. if it is still not oozing the tar, proceed. if it is, well then we will deal with it. If possible.
