Do tubes wear out faster at high volume?

[jezzbo]

Do they?
And why?
Since the audiosignal only disturbs the electronflow from anode to cathode (or is it the other way arround?) How can this reduce tube life?
(if it does).

Thanks for your thoughts / knowledge.

[Andy Le Blanc]

The electron stream is like a sandstorm, the plate gets blasted
and the cathode loses it ability to emit, the getter gradually is used up.
Voltage and operational conditions can make the tube more or less perishable
depending upon the application. I've seen some players use up their tubes
in three months, some never have to change tubes.

[jezzbo]

thanks for your reply.
Very interesting.
But are you saying that that playing at a higher volume reduces tube life?
(everything else being equal)

so is there more stress on a tube when you turn up the volume?

Sorry for this noob question.

[jelle]

Consider this...at high volumes there will be higher current. Current in the tube causes heat. Also the cathode coating will wear off faster.

This will reduce power as the effective cathode surface will be reduced and less electrons will boil off the cathode at transients. The tubes will get tired and old.

[jaysg]

...and it's worse in combo's because of the extra mechanical vibration.

[Cliff Schecht]

Yes, higher volumes will wear out the tubes faster.

Also, I think it's been mentioned on here before also that having your heater voltage too far away from the specified voltage will dramatically reduce the life of your tubes. I use a dropping resistor in EVERY amp I build to get the proper 6.3V or 12.6V to the tubes. If the voltage is too low then you are probably pushing your PT too hard and need to upgrade to a stiffer unit (that could easily be taken out of context!).

[David Root]

Higher the current, the more sand in the blast. It's that simple.

[iknowjohnny]

Yes, higher volumes will wear out the tubes faster.

Also, I think it's been mentioned on here before also that having your heater voltage too far away from the specified voltage will dramatically reduce the life of your tubes. I use a dropping resistor in EVERY amp I build to get the proper 6.3V or 12.6V to the tubes. If the voltage is too low then you are probably pushing your PT too hard and need to upgrade to a stiffer unit (that could easily be taken out of context!).

I went thru this when i built my first amp and asked about whether i should do something about my amp's 7v heater. Some said leave it, as it will not make enough difference in tube life to even notice. Others said use a diode, others a resistor, and still others telling me doing that is riskier than leaving it. What to believe?! What wattage resistor do you use?

[Andy Le Blanc]

Get a 5W rheostat (series) and dial it in, although I do like the sound of a diode.
They used to sell these little disc things you put in your light bulb sockets
to maximize lightbulb life.

It is good to stay withing the design max rating to achieve the longest life out of the device.

when you run your heaters hot you shorten the cathode lifespan, the
emitting coating is boiled off into the vacuum.

[jezzbo]

Hi All,

thanks for your replies.

I asked this question because I was thinking the following:

In a tube the electrons flow from cathode to plate. (or the other way arround?)
The audio signal is at the grid.
The audio signal at the grid disturbes the flow of the electrons from cathode to plate.
If you turn your volume control up you actually put more signal (current or voltage?) to the grid right?
But why would that result in a more electronflow from cathode to plate?

Is it right to say that the grid is some sort of gate that opens more when you put more signal to it?
So when there is a low signal on the grid it kind of block the electron flow from cathode to anode?

If this is true, than the grid not only disturbes how the electrons flow but also how much electrons will pas.

I'm I just talking nonsense?

Thanks guys!

[Rich M]

The electrons don't act like a "sandstorm" as their mass is negligible. Tube mostly wear out due to the cathodes losing the ability to emit these electrons (except the ones that fail due to poor manufacturing or vibration, as mentioned, which, in my experience, has been any tube made after 1990 ). I'm pretty sure the gradual aging is due to surface contamination (thermionic emitters are very sensitive to a surface contamination). This can be the result of time, heat, failing getter or ION bombardment (sputtering) of the tubes internal components that land on the cathode. In certain cases, one can also have the sputter removal of the special coating on the cathode, which will also degrade the cathode's ability to emit electrons.

In terms of overall lifetime, I think it depends on the class of the amp. True class A amps dissipate more power in the tubes at idle than at full power whereas class AB and B dissipate more at higher output. This additional heat load will drive the tube aging.

[Andy Le Blanc]

The effects high velocity electron bombardment could be a fun argument.

When you make a tube you have to institute an aging and stabilization process
to bring the tube to within the range of operational characteristics that are defined
for the device.

This is done with series of step to active the cathode, stabilize emission, and
de-gas the grids and plate.

You have be fairly cautious not to prematurely age to the tube. The purpose
is to remove gases which might be liberated under the normal operation of the tube.
A few things happen as the tube ages, the cathode coating sublimates into the vacuum,
any metal cladding on the grid wires also sublimates and gases
are liberated from the plate as it endures surface bombardment.
all of this ends up poisoning the vacuum and sublimes on to the surfaces inside the tube
reducing the efficiency and practical life of the tube.
Continued electron bombardment also creates thermal deformation of the
grid wires and gradually evaporates the anode surface.

I thought a sandstorm was a more poetic way to say this.

[Structo]

On my recent tube buffered FX loop I used a Fender stand alone reverb power transformer.

It is spec'd at 6.6vac on the heater winding and when I measured it, yep 6.6vac.

Is the extra .3v anything to be worried about?

Do I need to drop that voltage?

[tubeswell]

On my recent tube buffered FX loop I used a Fender stand alone reverb power transformer.

It is spec'd at 6.6vac on the heater winding and when I measured it, yep 6.6vac.

Is the extra .3v anything to be worried about?

Do I need to drop that voltage?

Most heater filaments will tolerate +/- 10%. I have several builds where the heaters sit at 6.5 or even 6.7, and they work just fine. If you get to about 7 you will start having issues and you need to think about something like back-to-back 6A diodes in series with the winding etc

[Merlinb]

Hi All,
But why would that result in a more electronflow from cathode to plate?

Because tubes are non-linear. The positive half-cycles get amplified a bit more then the negative half-cycles, so the average current when amplifying is actually slightly greater than at idle. In the case of class AB power valves the increase is even greater.
As others have pointed out, more current means the cathode coating evaporates more quickly. However, in the case of audio amps the difference in lifespan between an amp left running at idle and one running permanently at full volume is almost certainly negligible in practical terms. The expected lifespan of an average tube is 5000 - 10000 hours, and the average lifespan (which is not the same thing) is around 40000 hours.