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Here is the last amp in my bunch that is giving me problems (for now).
It is a little Magnavox 401 that I got a couple of years ago.
I replaced the filter caps, the cathode caps and the coupling cap. I put in NOS tubes that are all good. I even replaced the 6" speaker with an 8" Jensen.
The tubes are 20EZ7 preamp, UL84 power, and 36AM3B rectifier. This does have an isolation transformer.
Since doing these repairs, it worked beautifully for a year or so but started developing a mild buzz or hum.
I put it on my bench last week and after taking the chassis out the hum was even worse. If I plug a guitar in, the hum is nearly as loud as the guitar.
I call it a buzzing hum because it is very unpleasant. All hums are, but this seems different from poor grounding, filter caps or others I have experienced. My ears don't seem to work well enough to identify 60 vs 120 hum.
I am hoping someone can point me in the right direction for finding and correcting the cause here.
I will post a schematic and a gut shot as soon as the system will allow me to, as I have tried twice but it keeps failing.
It is a little Magnavox 401 that I got a couple of years ago.
I replaced the filter caps, the cathode caps and the coupling cap. I put in NOS tubes that are all good. I even replaced the 6" speaker with an 8" Jensen.
The tubes are 20EZ7 preamp, UL84 power, and 36AM3B rectifier. This does have an isolation transformer.
Since doing these repairs, it worked beautifully for a year or so but started developing a mild buzz or hum.
I put it on my bench last week and after taking the chassis out the hum was even worse. If I plug a guitar in, the hum is nearly as loud as the guitar.
I call it a buzzing hum because it is very unpleasant. All hums are, but this seems different from poor grounding, filter caps or others I have experienced. My ears don't seem to work well enough to identify 60 vs 120 hum.
I am hoping someone can point me in the right direction for finding and correcting the cause here.
I will post a schematic and a gut shot as soon as the system will allow me to, as I have tried twice but it keeps failing.
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