• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6V6 line preamp

diyAudio Chief Moderator
Joined 2002
Paid Member
Do this and you should have no hum. Your 6.3V secondaries aren't strong enough and you parallel those I suppose.
 

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Official Court Jester
Joined 2003
Paid Member
I just saw what Salas wrote about weak windings ........

you canconnect them in parallel , but!! securing that each 6V3 winding have own fixed resistor ;

so determine those resistors by trial and correct , going from higher value , that way that they're paralleled at tube heater

than take your Ub from whatever side of rectifier tube's cathode , as Salas posted
 
I just saw what Salas wrote about weak windings ........

you canconnect them in parallel , but!! securing that each 6V3 winding have own fixed resistor ;

so determine those resistors by trial and correct , going from higher value , that way that they're paralleled at tube heater

than take your Ub from whatever side of rectifier tube's cathode , as Salas posted

THe resistors before parallel point being an attempt to balance draw and reduce hum, as hum is essentially a difference or imbalance in voltage?
 
Official Court Jester
Joined 2003
Paid Member
THe resistors before parallel point being an attempt to balance draw and reduce hum, as hum is essentially a difference or imbalance in voltage?

even if that you have hum there (in heater circuit of rect. ) and you have it anyway - because you are heating it with 5V/60Hz hum in fact :rofl: .... fact is that that hum is floating , referencing to your audio power circuit

:devily:
 
Official Court Jester
Joined 2003
Paid Member
Exactly!. Actually, my secondaries are rated for 4A, so I think Salas is right that one can be eliminated, leaving the balancing act for another day....

if they're 4A , then OK


........ I ahev read that unused secondaries should be connected through a resistor to ground to prevent buildup. Am i delusional or is this something that is done?

no
just isolate ends

just another web legend , at least in this case

even in digital world , fully open unconnected winding is - nonexistent

Never thought about it like that.

just another proof that Ground is state of mind

it can be whatever you choose , and execute correctly
 
:cheers:Filament went bad on soldering iron. Just got cheapo radio shack to make changes. Changing to single secondary to filament made no changes in hum. Hoping the CT configuration on B+ secondaries makes a difference. Let you know in a bit, and thanks for asking. Its been a day from hell so I need something to work!