By now, most people know that twisting the AC heater wiring is recommended. But What happens if you ignore this?
I set up my PP 6P36S amp with AC heater wiring using a single conductor and the chassis for return.
It was wired from 12VCT with the CT grounded to chassis, each channels' tubes powered by one side of the coil. On testing there was a hum loud enough to annoy me. (about 10mV into 6R @ 60Hz). This was good by old standards really, but what about DC? So I rigged it up to use DC, full wave for 6V. There was 8V so I added a bridge to drop the voltage down to 6.3VDC for all 4 6P36S. I added 20,000uF of capacitance after the rectifier and bridge. Now the hum is louder, and at 120Hz.
Time for twisted pair on AC. Hum is %95 gone. The buzz of the power transformer is louder than any electrical hum. Just that easy.
For this test I also ran the VA/PI/Driver tube heaters from regulated DC.
The take away here is that high heater current output tubes can be better run from AC if you take the time to twist the wire I guess... Unless you're using an SMPS
I set up my PP 6P36S amp with AC heater wiring using a single conductor and the chassis for return.
It was wired from 12VCT with the CT grounded to chassis, each channels' tubes powered by one side of the coil. On testing there was a hum loud enough to annoy me. (about 10mV into 6R @ 60Hz). This was good by old standards really, but what about DC? So I rigged it up to use DC, full wave for 6V. There was 8V so I added a bridge to drop the voltage down to 6.3VDC for all 4 6P36S. I added 20,000uF of capacitance after the rectifier and bridge. Now the hum is louder, and at 120Hz.
Time for twisted pair on AC. Hum is %95 gone. The buzz of the power transformer is louder than any electrical hum. Just that easy.
For this test I also ran the VA/PI/Driver tube heaters from regulated DC.
The take away here is that high heater current output tubes can be better run from AC if you take the time to twist the wire I guess... Unless you're using an SMPS