Hey all,
I have built two separate tubelab se amps using 300b output tubes and one electron ubt-3 transformers.
Power transformer is Hammond 276 running on 120v primary to decrease voltage.
B+ 400v and no higher, -bias -230v, driver tube plates adjusted easily to 175 roughly. Bias current is stable and easily adjustable.
The filament regulator has 6v on it and doesn't seem to be dropping out at all.
Both boards Hum! When the amp is fired up, the tubes war and a hum starts, but gets quieter as the filaments settle. I am left with a 60hz hum with some buzz that moves the cones pretty good.
I find at the tubes, there is about 400mv ac in the dc supply and about 300 in the 5v heater supply.
Using a bench supply to the b+ rail with the rectifier out, amp is dead quiet and works great. I have swapped rectifier tubes already, made sure they were placed correctly with proper voltages in each pin. Swapping power transformers makes no difference, changing grounding does nothing, and adding capacitance to the b+ or the heater supply change nothing either.
The hum is present with the driver tubes out and gets way louder as bias is increased. The mosfets seem to get hot.
I am shaking my head not knowing what I should do now. Anything would be appreciated
I have built two separate tubelab se amps using 300b output tubes and one electron ubt-3 transformers.
Power transformer is Hammond 276 running on 120v primary to decrease voltage.
B+ 400v and no higher, -bias -230v, driver tube plates adjusted easily to 175 roughly. Bias current is stable and easily adjustable.
The filament regulator has 6v on it and doesn't seem to be dropping out at all.
Both boards Hum! When the amp is fired up, the tubes war and a hum starts, but gets quieter as the filaments settle. I am left with a 60hz hum with some buzz that moves the cones pretty good.
I find at the tubes, there is about 400mv ac in the dc supply and about 300 in the 5v heater supply.
Using a bench supply to the b+ rail with the rectifier out, amp is dead quiet and works great. I have swapped rectifier tubes already, made sure they were placed correctly with proper voltages in each pin. Swapping power transformers makes no difference, changing grounding does nothing, and adding capacitance to the b+ or the heater supply change nothing either.
The hum is present with the driver tubes out and gets way louder as bias is increased. The mosfets seem to get hot.
I am shaking my head not knowing what I should do now. Anything would be appreciated
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