[Tube-Swap] Why 6.3V heater?

[Brian Carling]

On 2 May 2004 at 11:26, W0rw@aol.com wrote:

> See http://www.harpamps.com/micKtubes/Why-6.3V-Filaments.html


Paul - part of his explanation is pretty incomplete or 
even misleading though...
The claim is that using more than 6.3V will shorten the life or 
even damage the tubes.

In my many years of working on tube audio amplifiers, 
I see no evidence that a small increase in filament voltage 
will have these deleterious effects.

Many 6V tube heaters are fed with 6.5 to 7 volts AC, especially
since the older equipment was designed to run on 110V
or 115-117V AC and todays line voltage is typically 
anywhere from 118 to 128V AC in most areas.

I have seen 6v tubes run happily on 7V AC or even more 
for years.  However, it's better to be safe than sorry and 
it IS best to keep them down around 6.3 to 6.5V.

Applying 5V AC might in some cases reduce emission to 
the point that an oscillator stops, or that bad distortion 
might ensue etc.

YMMV - 73 - AF4K

QUOTE:

Applying more than the nominal voltage will shorten the 
filament life, or simply melt it. Applying slightly less 
(e.g. 5 V) will extend the tube (valve) life, but lower output 
power and amplification.

Jos