Another new project, valve pre-amp for my turntable

[g8ina]

If they are never used NOS, why would you still need a test report, in case they are a bad batch or deteriorate over time?

Yep, they can go "soft", ie, lose some vacuum.

[Zak33]

/cough

//cough

finished, a bit noisier than I expected, but got that great bottle warmth

what on EARTH is "bottle warmth"?

Please illuminate me

[g8ina]

It's a technical term, you wouldn't understand.









actually, it's due to the valves producing ODD harmonic distortion, as opposed to semiconductor amps producing EVEN harmonics. My own belief is that the human ear itself produces ODD harmonics which means valve amps *sound* nicer, better, sweeter, warmer, more open, more natural, thay also have MUCH more headroom, its VERY difficult to clip a valve amp

But if you don't believe me, you, or anyone else interested, is more than welcome to come have a listen

edited to swap odd/even.

[peterb]

Cough. Its actually a bit more complicated than that . It is also it because valve amplifiers tend to be in a class B configuration with a push/pull output via a transformer to match the high impedance output of the valve to the low impedance of a loudspeaker. That suppresses even harmonics, which sound very harsh to the ears, and the transormer itself limits the higher order odd harmonics.

You can achieve the same effect with solid state amplifiers, but because they are inherently low impedance devices, they don't usually have a transformer output. You still get the even harmonics suppressed, but to a lesser degree without careful circuit design.

https://en.wikipedia.org/wiki/Push–pull_output

[g8ina]

Typical, cant tell left from right as per blooming usual. Swap even for odd and vice versa, thanks Peter !

[Millennium]

I feel the need to power on my amps again. If anyone wants to have a listen to my World Audio Design KT88 based amp (but apparently not their KT88 or KAT88 models, it has 3 knobs on the front, maybe someone can help me identify the model designation?) let me know and I'll arrange it. I'm in Hammersmith W6.

Valves truly sound sweet.

NB: Please don't ever power on a valve amp without speakers connected to it properly. They can be damaged.

[Zak33]

but bottle....

bottle?

why on earth bottle?

As in Hot Water Bottle? That type of warm?

[DanceswithUnix]

but bottle....

bottle?

why on earth bottle?

As in Hot Water Bottle? That type of warm?

Perhaps because if you tell a valve enthusiast that their amplifier sounds nice because it is generating loads of third harmonic distortion, they will bottle you

I thought valves were commonly called "tubes", but that didn't make much sense to be either.

Edit: Actually third harmonic is in guitar amps which are commonly overdriven into distortion on purpose, in a hi-fi it would be lower levels of second and 4th, but IIRC the distortion levels are always magnitudes higher than expected from a modern semiconductor amp. TBH I'm surprised it isn't just a DSP setting on modern surround amplifiers.

[peterb]

Perhaps because if you tell a valve enthusiast that their amplifier sounds nice because it is generating loads of third harmonic distortion, they will bottle you

I thought valves were commonly called "tubes", but that didn't make much sense to be either.

Its not that they generate third harmonic distortion, but they suppress even order harmonics.

I think the term bottle comes from the shape of some of the older valves like the 807 or KT66.



Miniature valves like the EF80 looked more like tubes,



and the subminiature acorn valves were called acorns because thats what they looked like!



(Hint - the one in the middle IS an acorn! )

[DanceswithUnix]

Its not that they generate third harmonic distortion, but they suppress even order harmonics.

But that means generating even order harmonics to start with, and does anyone make an amp these days that does that? I mean, that argument would have held in the 1970's and maybe even in the 80's to some degree but really I haven't heard a bad amplifier in decades.

Now you are going to tell me that the acorn is in that photo as it has a really warm sound

[peterb]

But that means generating even order harmonics to start with, and does anyone make an amp these days that does that? I mean, that argument would have held in the 1970's and maybe even in the 80's to some degree but really I haven't heard a bad amplifier in decades.

Now you are going to tell me that the acorn is in that photo as it has a really warm sound

Any non linear device will generate harmonics (or strictly speaking, any device with a non-linear transfer function) and that includes valves and transistors except over a small part of the operating range. That’s why the different bias arrangements or class of amplifiers were developed, and why overdriving a pre-amp cause distortion, because it drives the device into a non- linear portion of its transfer function.

Even order harmonics are particularly unpleasant tithe human signal processing system.

[DanceswithUnix]

Any non linear device will generate harmonics (or strictly speaking, any device with a non-linear transfer function) and that includes valves and transistors except over a small part of the operating range. That’s why the different bias arrangements or class of amplifiers were developed, and why overdriving a pre-amp cause distortion, because it drives the device into a non- linear portion of its transfer function.

Even order harmonics are particularly unpleasant tithe human signal processing system.

Yep agree with most of that, except AIUI you need higher order harmonics to get really unpleasant which was the mud slung at old solid state amplifiers, there was loads of feedback used to improve linearity which pushed any harmonics up in order which sounds nasty. In my youth when power amps meant hand matching 2N3055 output devices to get any hope of linearity that makes sense, but with modern FET devices I don't see it.

Reading around just now there was an interesting article (https://phys.org/news/2017-02-physic...alve-amps.html) which described how guitar valve amps are commonly used on the limit so that the player can switch from just clipping the top of the waveform to generate even harmonics into full clipping generating 3rd harmonics, using the valves as part of the instrument. I know hi-fi doesn't clip and isn't the same, but just shows low even harmonics can't be that bad if guitarists are aiming for it.

[peterb]

Yep agree with most of that, except AIUI you need higher order harmonics to get really unpleasant which was the mud slung at old solid state amplifiers, there was loads of feedback used to improve linearity which pushed any harmonics up in order which sounds nasty. In my youth when power amps meant hand matching 2N3055 output devices to get any hope of linearity that makes sense, but with modern FET devices I don't see it.

FETs designed for audio can be very linear, although they tend is towards Class D amplifiers - essentially switching amplifiers - for increased efficiency. The incoming audio is modulated to produce a PWM stream. The PWM stream is amplified using a switching amplifier and then filtered (integrated in mathematical terms) to provide the audio output.

Reading around just now there was an interesting article (https://phys.org/news/2017-02-physic...alve-amps.html) which described how guitar valve amps are commonly used on the limit so that the player can switch from just clipping the top of the waveform to generate even harmonics into full clipping generating 3rd harmonics, using the valves as part of the instrument. I know hi-fi doesn't clip and isn't the same, but just shows low even harmonics can't be that bad if guitarists are aiming for it.

Depends on the sound they are aiming for

[BurchSung]

Hi...i am a new user here. In my amp 12AUX are really pretty good, they are the Telefunken ones but after many hours of use I'm totally unsure if they're too warm or too useful or whatever. One thing I know is that they would be hard to replace, even like for like.I am not even sure if I would replace them with Mullard or such to be honest.