Heater Question

[jeff]

 My local tech brought something up today I'm not sure I get. He said that with regaurds to the 12AX7s heaters, All 4&5s should connected to one wire and all 9s should be on the other. I never even thought of this before but is this less noisey than randomly attaching them? Each wire is 3.15 refrenced to ground.

[bobmegantz]

I can't imagine it would make much, if any, difference.  What does make a difference, however, is how the wires are routed to the pins and the order in which the tubes are wired...

[jjasilli]

Published amp guru's recommend consistently with heater polarity.  Audible results may vary from amp to amp.  (For rectified DC heater supply, consistent poalrity appears to be mandatory.) 

[RicharD]

I'll bite. 

It makes absolutely no difference.  All the filaments do is get the tube hot enough to conduct.  If you experience filament noise you've either got a bad layout or bad grounding.  Typically with Dc filaments you'll see them all wired the same way but that's usually just to simplify the layout, it doesn't matter.  I've also heard it argued you should reverse the filament polarity of every other tube so as to cancel out the filament noise from the previous stage.  It doesn't matter.

[tubeswell]

I've also heard it argued you should reverse the filament polarity of ... 

Apparently this is supposed help in the output stage of a PP amp but I've never conscientiously tried to wire my heaters this way to find out. According to Hoyle, if the opposite sides are wired 'opposingly', any heater AC should be cancelled out in the OT primary.

However, whilst this may hold 'true', I am a bit sceptical as to the benefits, because the amount of heater AC getting into the signal via the cathodes at the push-pull end of the amp relative to the signal strength happening in that stage is a lot less than it is at the pre-amp end of the signal path. Might be a great idea for Hi-Fi (although most Hi Fi amps are SE from what I gather)

[jeff]

Reverse on the PP output tubes. That makes sence.

Wait. If the noise is the opposite and they go to out of phase sides of the transformer it would add. If they were the same then they'd cancel. So you'd want to go pin 2 to pin 2 7 to 7.