parallel SE, Class A build: hum
Posted: Sat Feb 13, 2016 8:31 am
marnin, yawl (that's mississippi for hello)
finishing up my first custom circuit build (cathode bias, class A with 5881 and toggle to activate 2nd 5881 in case of emergency, has full assortment of treble bass mid controls [5f8-a tone stack] all in a tweed vibrolux box w/ alnico 10, 20 watt OT). She's passing a nice full signal but with what sounds like a 60 Hz hum in the power tube section.
I grounded all of the following to a single point:
1. filter caps
2. red/yellow PT center tap
3. power tube cathode bias assembly (this is the one I currently suspect as needing to be separated given its proximity to signal... does this sound
like something I should ground to another location?)
I double checked my heater pairs, they hit the same pin #s on both 5881s and the same ones on the 2 ax/ay7s (I don't recall if they are supposed to alternate for example pins 4/5 on v1 go to pin 9 on v2 or if pin 4/5 on v1 should go to pin 4/5 on v2 etc)
I don't have a choke installed.
The heater has a center tap (green yellow) that I soldered to the inside wall of the chassis with my 80 watt solder canon.
Got to nail down that blasted hum!!
finishing up my first custom circuit build (cathode bias, class A with 5881 and toggle to activate 2nd 5881 in case of emergency, has full assortment of treble bass mid controls [5f8-a tone stack] all in a tweed vibrolux box w/ alnico 10, 20 watt OT). She's passing a nice full signal but with what sounds like a 60 Hz hum in the power tube section.
I grounded all of the following to a single point:
1. filter caps
2. red/yellow PT center tap
3. power tube cathode bias assembly (this is the one I currently suspect as needing to be separated given its proximity to signal... does this sound
like something I should ground to another location?)
I double checked my heater pairs, they hit the same pin #s on both 5881s and the same ones on the 2 ax/ay7s (I don't recall if they are supposed to alternate for example pins 4/5 on v1 go to pin 9 on v2 or if pin 4/5 on v1 should go to pin 4/5 on v2 etc)
I don't have a choke installed.
The heater has a center tap (green yellow) that I soldered to the inside wall of the chassis with my 80 watt solder canon.
Got to nail down that blasted hum!!