Do valves burn in?

[Marco]

"Bint" - lol... Such an endearing term of affection!

Marco.

[The Grand Wazoo]

From The Grave

[Reffc]

"Burn-in" as applied to anything audio interestingly seems to have it's roots in the final stage of valve production where the Barium getters needed to be flashed and the valve required heating to activate the Cathode coating with a final oven-bake as part of the sealant curing process. There were several stages as I understand it. Coatings are first activated, a vacuum applied to remove the gas (whilst an RF induction coil was placed over the valve to help liberate stray gases and flash the barium getter). The valve base is then sealed with a cement and the valve "burned in" in an oven to harden the sealant and left to cool (anneal) to de-stress the internals. That's the "burn-in" prior to electrical testing under load to help eliminate duds.

When the consumer finally receives the valve, there will be in initial bedding in period where the valves may be biased (in the case of power valves) and the sound will change over time as basically the valve wears out (thousands of hours typically) so the only burn-in that makes sense to me is the first 30 minutes or so after valves are settled, properly biased etc, whilst they come up to optimum operating temperature.

[Jazid]

Being boring I am reading the Radiotron Designers Handbook at the moment; I find plenty of reference to valves changing over thier first hundred hours or so (and thereafter for life), complete with specs that demonstrate this and causes too. If the 'Bible' is to be believed it isn't foo, its old fashioned science. In their case they are of course referring to valve function rather than sound of course, but the variance is certainly enough that it would affect sound.

[Reffc]

Being boring I am reading the Radiotron Designers Handbook at the moment; I find plenty of reference to valves changing over thier first hundred hours or so (and thereafter for life), complete with specs that demonstrate this and causes too. If the 'Bible' is to be believed it isn't foo, its old fashioned science. In their case they are of course referring to valve function rather than sound of course, but the variance is certainly enough that it would affect sound.

Yes, some valves can change over that timeframe (I have the same book!) and technically a valve's spec alters slowly from new to end of life, but given that the life of many preamp driver valves (say) can be 8000 or more hours, you'd need very golden ears to pick out changes I think. I've had some new 12AX7s that haven't altered sound wise at all (not that you'd notice) in the first 100 hours or so. The fact that some valves change over the first 100 hours may not always correlate to audible differences but there are some output valves where it can be noticeable within the first 50 or so hours depending on the circuit they're in.

[Jazid]

Hmm, seems to me that the drift in signal valve grid current and zero bias point is a good case in question. I agree they aren't supposed to change, but they do. Also agreed you would have to be golden eared indeed to hear the change as it progressed, but sure as lies from politicians you'd hear it when you replace the tubes for others 'elsewhere in their journey through life'!

[StanleyB]

Also agreed you would have to be golden eared indeed to hear the change as it progressed, but sure as lies from politicians you'd hear it when you replace the tubes for others 'elsewhere in their journey through life'!

If you can't hear the change then you should not invest in a valve amp. The extra running cost would be wasted on you. A reasonably seasoned valve amp audiophile can tell the difference between valve sound in a blind test. You can't say the same for a blind test with transistors.

[Jazid]

If you can't hear the change then you should not invest in a valve amp. The extra running cost would be wasted on you. A reasonably seasoned valve amp audiophile can tell the difference between valve sound in a blind test. You can't say the same for a blind test with transistors.

I think you misunderstand me, I am not saying that you need good hearing to tell a valve amp from a s/s one, rather that you would need something that pretty much all blind testing so far has shown people not to posess; A reliable long term aural memory.

However we do posess long term reliable sensitivities to stress and fatigue which might explain why valves used for amplification of music continue to sell to people who consider this characteristic significant whereas they are rarely used in any other kinds of equipment.

I would suggest that this sensitivity explains in part why people are prepared to stump up the extra money and ongoing maintenance costs for valve amps. YMMV of course..

[Clive]

However we do posess long term reliable sensitivities to stress and fatigue which might explain why valves used for amplification of music continue to sell to people who consider this charachteristic significant whereas they are rarely used in any other kinds of equipment.

I would suggest that this sensitivity explains in part why people are prepared to stump up the extra money and ongoing maintenance costs for valve amps. YMMV of course..

I've used valves for year and have just switched my power amps back to SS though it's still SE. Maybe a more telling characteristic is low or no feedback.

[Firebottle]

I don't get this penchant for no feedback
Admittedly I haven't heard any zero or low feedback amplifiers, but I thought feedback lowered noise and distortion, and increased linearity and bandwidth.

Is that a bad thing

Sorry if I'm opening a can of worms, Alan