Discussion in 'Amps and Cabs' started by Antiquo Cantor, Feb 24, 2016.
Any tube can lose its vacuum - that's not exclusive to power tubes. It is very easy to visually inspect the getter coating and assess if the vacuum has failed.
If we want to discuss pre-amp tubes, that's when things get more complex. Changing the V1 in an amp that has twelve tubes and a three page parts list will not show-up the sound/tone shifts nearly as readily as an amp that has only three tubes and a dozen or so components.
Components themselves can make a big diff, say we build two 5E3 amps that are exactly the same in all parts/chassis/wiring layouts.
In amp #1, we use all 2% tolerance caps/resisters, and in amp #2 we use all 10% caps/resisters,, which one will sound "better" to our ears?,, now lets add in the effects of heat, because the drifting of values will affect the responce of the tubes, and diff tubes will have diff curves, even though they are "supposedly" within spec.
In the old days of ham radio we were constantly fussing with the controls, trying to stay on frequency as the various components went thru heating/cooling cycles,, amps do the same, we just can't control it beyond trying to tweak the bass/mid/treble, which are somewhat crude/wide swath controls.
I'll use inexpensive NOS rectifier tubes and a few NOS preamp tubes (usually the lower gain varieties, like 5751 and 12AY7....there are plenty of nice new manufacture 12AX7 types available today), but never NOS power tubes. The cost/benefit is just not there any longer for NOS power tubes, IMO.
All tubes lose their vacuum over time. It's called permeation, a similar process to gaseous diffusion - kinda like a lot of what's going on in this thread Naturally, this occurs faster and to a greater extent in "larger tubes". such as power tubes because they have more surface area and the bottle (membrane) thickness is less with respect to surface area for a given vacuum than in a 12AX7 for example. Even so, any tube that's 50 years old is going to have been subjected to some reduction of vacuum over such a long period of time. That reduction of vacuum is going to yield some reduction of performance that is likely to be interpreted as some kind of performance benefit (warmer, softer, smoother sound...) Since even with genuine NOS tubes, nobody here can say "I compared a brand new, fresh off the production line UK Mullard EL34 of a specific transconductance to a reissue Mullard EL34 with the same tranconductance", it's really a moot discussion. Trying to do any kind of comparison using a guitar amp as some reference standard is even more likely to produce irrelevant results.
With age brings spice baby! 55 and still young. And as for tubes, who knows why, if it's even true.
I can see your point. But I have to disagree about the reduction of vacuum... Getter material continues to react with gases and remove them as they're freed. As long as getter remains, the vacuum remains generally constant. But once the getter is spent, the vacuum would eventually be lost.
Didn't read all but a few that seemed to say something similar as I.
Something that is sometimes forgotten about tubes is, as a tube ages, they will lose their treble response over time.
Especially preamp tubes.
It happens slowly so you may not notice the change or if you do you just turn the Treble up on the amp.
Sometimes this is mistaken for a nice tone or a less harsh tone.
I'm glad that people like their amp after a tube change because the alternative is solid state.
It is important to distinguish between use and aging. The loss of treble you're describing is due to use. Unused tubes that are simply aging do not exhibit this treble loss.
Tube Quality is related to how well they have been constructed.
In no particular order - the liquid metal formula was unique, the
vacuum created inside the class was truer; and the physical construction
of the tube was of a higher quality.
The sum of those processes produced higher quality tubes.
el84s wear out sooooo fast...i hope you didnt pay a lot. those are the last type of tube id ever pay a premium for.
my explanation is the placebo effect. im guessing if you heard recordings of your amp w the expensive tubes and the regular tubes you wouldnt be able to tell the difference.
im unaware of any current production amps that were designed and fine-tuned for NOS tubes. sort of makes you wonder what type of design functions better using parts that werent intended to be used...
That's a pretty important qualification.
No it didn't.
ohhhhhh! burn! lol, so silly. what was the point of that? i cant claim that statement was anything but a guess bc i dont really know him, i just recognize the blind unquantifiable devotion and testimony of the placebo effect.
It's actually not the getter that does this but the barium coating inside of the top (and often sides) released by the getter during production. Yes, it's main purpose is to continue maintaining a certain level of vacuum, though its capacity is not infinite, and this is mostly with respect to those gases released by the internal electrodes where those gases were initially absorbed and later released by heat,etc. And for sure that process slows over time as the coating deteriorates. Also, it cannot absorb all gases equally, or at all in some cases. Thus, a NOS tube can in fact age without ever being used. It's less evident than tubes that have seen moderate to considerable use, but I'm willing to bet money that most participants here have never auditioned a genuine virgin NOS tube compared to a CP counterpart of similar performance in a guitar amp. Theory is nice but reality bites
One can adopt any position, based on unproven assumptions and projections. My point: actual experience is much more valuable (in my opinion).
experience and opinion are equally as meaningless when youre discussing an unquantifiable property. your comments to me are almost completely with out regard to what i said like youre arguing w someone else to me.
That barium material is the getter that I was referring to. The getter supply structure is often mistakenly thought of as the sole referent of this term. But in original tube manufacturing documents, the deposited gas-absorbent material is the getter, and it has an on-going active presence within the tube.