Valves: Can you try them out?

[Sporky_McGuffin]

I don't think it would be that unreasonable to ask, but I do suspect I know what the answer would be.

[MrMenturm]

ehehehe. Well yeah, anyone has the right to refuse a sale!

[Pendragon]

It's an interesting discussion, because we all often look at the range of valves out there, and find ourselves wondering whether it really is worth it, am I going to hear a difference, am I wasting my money, etc...

Is there something in the DSR's that says that "components" cannot be returned within a grace period, or have I got muddled up?

Good point ... what about p/ups, can you return them under DSR?

I've always assumed p/ups and valves could not be returned, but I've never actually asked.

[MaxTheMac]

interesting subject....

i would guess that any argument against DSR would have to rely on the concept of wear&tear of goods.... or the goods being defined as "consumables" and no longer being new....

for example, I wouldn't expect (although i might be able, but have never tried) to be able to send back a set of car tyres once they'd been fitted to the car, unless faulty.

the argument being, that putting them on the wheels, and driving say 30 miles, makes the item unsaleable as a new product, by virtue of wear .

okay so, you're maybe not going to lose much by running a valve for an hour or two, , but the pedant arguing the toss about not refunding, might raise the nature of the product and it's similarity to a light bulb in it's operation..... although irrelevant in the short term and practicality, still an argument that might be held valid in the madness that is the legal system....

DSR is intended to allow you to return goods in the same condition they left the retailer.... not minus a few hundred thousand electrons at one end....

if you see what i mean....


(note, i do not subscribe to that view... I'm merely hypothesizing what an uncooperative seller might argue... )

[ecc83]

MacTheMax,

I am not a physicist but I do not think cathodes can "lose" electrons. Seems to me that it is simply a thermal "pump" that keeps them flowing around the circuit?

For sure valves lose emission over the years and the process is so slow that it is barely detectable in much equipment, a hi fi amp for example will have enough negative feedback that gain will stay pretty stable, distortion gets worse but since the 0.1%THD of a really good valve amp is some 10 times better than it really needs to be the valve can get pretty poorly before the punter notices. One area where valve wear was immediatly noticed was in the local oscillator of valve radios when this would just stop. But back in the day when valves were good this took fekkin AGES to happen, decades in some cases.

My point, if I have not explained it before, was that maybe the threat of valves being returned en mass would stop some of the outlandish sonic claims by some suppliers?

Dave.

[ICBM]

I am not a physicist but I do not think cathodes can "lose" electrons. Seems to me that it is simply a thermal "pump" that keeps them flowing around the circuit?

That's nearly correct - the electrons are provided by the power supply, not the cathode... the cathode is simply an emitter, in the same way as a hose nozzle emits water but the water comes from the main. It's not a "thermal pump", though - it supplies no energy to the electrons, it's just that in order for them to be emitted it needs to be hot. The energy is supplied by the potential difference between the plate (anode) and the cathode.

The reason they lose efficiency over a long time is because the special mix of chemicals in the cathode coating - which are carefully chosen to maximise emission at what is still a relatively low temperature - slowly degrades.

This is also what I think is the main cause of the performance difference between old-production and new-production valves - the formulas for the cathode coatings took decades to evolve and were almost "secret recipes" known to the old manufacturers. If the new companies haven't got them exactly the same, the performance will be different. (Even disregarding other dimensional or materials changes which there may be as well.)

My point, if I have not explained it before, was that maybe the threat of valves being returned en mass would stop some of the outlandish sonic claims by some suppliers?

Some of the suppliers don't even seem to like to take provably faulty valves back, so I'm not sure how enforceable it would be.

[ecc83]

Sorry IC, think you are wrong there!
It is indeed the thermal energy that ejects the electrons and even in the absence of any anode volts they will form a "cloud" around the cathode called the space charge, the size of which is limited when the negative cloud charge equals the energy of an electron trying to escape.

A fair analogy is water evaporating. One in a few billion molecules will have enough energy to escape into the atmosphere at 10C but most are depressed by the air pressure. Pump in some heat and the mean free path speed goes up until at about 100C they all bugger off!

Re cathode materials. I don't know if modern valves survive catastrophic failure long enough these day to get a good idea of their longevity!

Heh! MAYBE it is time for a GOOD solid state amp!

Dave.

[ICBM]

Heh! MAYBE it is time for a GOOD solid state amp!

It's been "time" for at least thirty to forty years...

Just that for whatever reason, no-one seems to have properly analysed what it is that makes valve amps sound the way they do. I don't believe there's any fundamental reason a solid-state amp can't be made to sound the same, as you probably know! (Although someone, I think it might have been jpf, did mention grid conductance as a characteristic of valves that doesn't occur with transistors and may be important.)

The other thing that I think is still a problem with solid-state is that it's more difficult to 'user tweak'. I know the vast majority of valve amp users don't, but some of us do like to swap valves and rightly or wrongly do feel that it makes a difference to the sound. I like that ability to 'fine tune' things. OK, with an IC-based solid-state amp you can do the same thing if the builder uses sockets, but only up to a point.


(Still disagree about the "thermal pump" too - yes, the electrons "boil off" the cathode when it's hot and form a 'space charge', but the energy to drive them round the circuit comes from the power supply, not the heat. You can't make the current flow without the voltage no matter how hot the cathode.)

[ecc83]

Sorry IC, still disagree in the context of Max's post...

"DSR is intended to allow you to return goods in the same condition they left the retailer.... not minus a few hundred thousand electrons at one end...."

You are not "using up" electrons. You are taking a tiny fraction of the life off the valve but in the context of the "bathtub curve" it is not computable, in any even I am convinced that many of the ills that afflict modern valves are due to an inadequate burn in time at the factory. You could be said to be doing the supplier a favour!

Electrons are indeed "boiled off" the cathode, but to stay with the water analogy, nothing is ever lost*. What goes around, comes around. Anything will emit electrons if you get it hot enough, valve cathodes are just a few billion times more efficient than anything else.

* 'Cept Helium. We should not be using it for "entertainment" or even lift ballons.

Dave.

[ICBM]

Sorry IC, still disagree in the context of Max's post...

"DSR is intended to allow you to return goods in the same condition they left the retailer.... not minus a few hundred thousand electrons at one end...."

I must have missed the line about the DSRs - we were arguing about different things .

Electrons are indeed "boiled off" the cathode, but to stay with the water analogy, nothing is ever lost*. What goes around, comes around. Anything will emit electrons if you get it hot enough, valve cathodes are just a few billion times more efficient than anything else.

The point being that the electrons are not supplied "by" or "from" the cathode material - they come from the power supply, exactly as the hose nozzle does not supply water. So you can't "use up" the electrons.

You are not "using up" electrons. You are taking a tiny fraction of the life off the valve but in the context of the "bathtub curve" it is not computable, in any even I am convinced that many of the ills that afflict modern valves are due to an inadequate burn in time at the factory. You could be said to be doing the supplier a favour!

Yes, exactly.

* 'Cept Helium. We should not be using it for "entertainment" or even lift ballons.

And hydrogen, although there's more of it. Or does it get replenished from stuff falling into the atmosphere as well? I can't remember.