Running tube heaters at 6.0 volts?

[pqt_bach]

Hi all,

Will running tubes at 6 volts work as well as 6.3 volts?
Since AC is varying I guess it'll be OK but I just wanted to check. I'm planning on using a regulator for 6VDC

[bancika]

yeah, no problem. I've been using 6V reg. too. You can put a diode between center pin and ground to increase voltage for 0.3V, but it's ok as it is

[pqt_bach]

Cool, thanks

[Ronsonic]

The tube manufacturers considered +/- 5% to be perfectly acceptable.

Ron

[JimRayden]

In fact, it's usually 10-20%, so you're safe here.

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Jimbo

[JonFrum]

Just to add to the confusion     I've only ever seen 10%. +20% would have a significant effect on the life of the filaments. I've seen a graph of heater life over different voltages. beyond 10% in either direction, the curve drops dramatically.

[JimRayden]

http://www.pmillett.com/tubedata/HB-3/Receiving-Type_Industrial_Tubes/6681_12AX7.PDF



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Jimbo

[alextheian-alex]

The tolerance % is dependan on the tube and it ranges from 5% to 20%.  Overvoltage by more than the specs will shorten the lifespan of the tubes, but undervoltage will not really hurt the life TOO much as long as it is an oxide/indirectly heated tube; tungsram and directly heated cathode tubes will die much quicker with undervoltage.  If you run oxide-cathode tubes like 12ax7, 12au7 etc on lower heater voltages, it just changes the emission and bumps the specs around, making the published plate curves in the data sheets useless.  it can work fine though if you know what you are doing, or if you can get a set of curves at the lower voltage.  Vox makes a line of tube pedals that run the heaters at 50%, which drops the current draw down (ohm's law) and Neumann and Sony ran the tubes in some of their ridiculously expensive mics at lower than spec heater voltages.