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Question on what is more important B+ or Plate Voltage

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You'll have to ask someone who believes in it. :D I'm pretty skeptical, having attended hundreds of concerts with all sorts of amplification used (some of it really quite awful) and never having heard a timing problem. Many other problems, sure, but never an issue with timing unless the musicians were having an off night.

The very worst was a no-name PA system used at the old Famous Ballroom in Baltimore for their Sunday shows. Spiky, gritty sound, laughable frequency response. Yet somehow, the subtle timing play of people like Dizzy Gillespie, Miles Davis, Sun Ra, Roland Kirk, and Dexter Gordon came through perfectly, week after week.
 
John65b,

A long time ago in a green valley far from here ..... you asked about plate voltage/B+ voltage. Since this is your thread, I will try to return to some further points here from the southern tip of the planet (OK, Aussies, calm down - I know. But we will talk again after the World Cup..... Oops!!)

The best plate (anode) voltage is roughly somewhere half-way between B+ (no plate current) and where G1 to cathode is 0V. That means that the plate can swing maximally without "hitting against something" either below or above. But in a pre-amp where the signal is typically small, an optimum point may be a somewhat lower Va. All this subject to further conditions, but to try to give an idea. It also has to do with lowest distortion, obviously, but that kind of co-incides with the above.

Sy's suggestion of a constant-current source (ccs) means that the higher anode voltage peak won't "starve out" as a result of plate current running out of steam. A very simple explanation, since I do not know your level of electronic knowledge.

Regarding PRAT: Thanks, now I also know what it is.

Methinks both Mach1, and Sy (+ others) had a point, but in the (broad) context of a pre-amp discussion (full stop): I cannot but feel that genre-designated equipment has its place - literally. I would not like my amplifier (in this case) to be this-music or that-music friendly, but as the universal ideal of hi-fi is supposed to mean: It must neither add to nor subtract anything form the original. Naturally folks can buy what they want; it is their money. But for whose taste must I design?

I often use the example: When a guitarist wants a guitar amplifier to provide his brand of sound, you design in whatever distortion he wants (and brother, did I have to do weird and funny things to that end; twisted my guts) - but when he listens to a recording of his music at home, he wants a "blameless" amplifier. No PRAT then, if I understood correctly. I got the impression that John65b was after the latter.

Although modern electrolytics are quite good, my experience is also that it is advantageous to make up say 10 000uF of smaller ones. (To boot it is also more convenient to fit them in on a pc board.)
 
I guess that the PA and instrument amps used at jazz, rock, and bluegrass concerts must have great PRAT because I don't recall ever experiencing a lack of it with great musicians playing live.

Whenever I've gone to a live concert, I was under the impression that each musician had his own amp/speaker combo, not one for the whole group as you would find in home stereo. The amp/speaker used in a concert is in effect the instrument itself and what a recording of a live concert does is capture what comes from those PA systems. PRAT has nothing to do with them. Comparing a studio recording using strictly acoustical instruments to a live performance that uses amplification is nonsensical.

By the way, john65b, your second best bet for getting rid of your hum is to divide your filter into multiple sections. Your best bet is to spend some money.

John
 
not one for the whole group as you would find in home stereo.

Depends on the venue, but most of the jazz clubs and rock concerts I've been to had a single PA system. - everyone had their own amp, but the amps were smaller, miked, and fed through a large PA. I believe it works the same way at musical theater and opera where performers are miked.

The days of Marshall stacks filling an arena are long over, I'm afraid.
 
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Speaking of concerts, I am going to Def Leppard, Styx and Foriegner concert on Friday. Not exactly my cup of tea (prefer Diana Krall, Dave Mathews, or anything Jazz) but I thought, why not expand my horizons a bit. I have to remind myself to bring some earplugs and sit far enough away from the cloud of "wacky tabacky" in the air since I get drug tested at work. How things have changed.

The first album I ever bought was a Def Leppard "High and Dry" and Ted Nugent in the early eighties. How my musical tastes have changed for the better (still enjoy Terrible Ted tho).
 
12B4 plate curves

I'm a bit bored at work...this may be a little on (or off topic)...

This hasn't been shown yet, and will clear any doubt...
12B4 curve with ~8k2 load line at B+=235V...(tube could be pushed a little harder to make sure it in a more linear region, but it looks ok now)

Looks like as long as your plate voltage stays above 50V you'll be fine. Any lower, and your grid may be near current drawing region...

Very nice tube (curves)...i'm considering it for a preamp now as well.
 

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mach1 said:
PRAT, as original used on this post stands for Pace, Rhythm and Timing.
There are those that claim that some audio components (amps are often cited) are better than others at preserving the PRAT inherent in some forms of music (ie its rhythmic integrity).

In the other camp are those that claim there is no inherent difference between components in their ability to accurately reproduce rhythmic information, and that the effect is purely a physco-acoustic one induced by marketing hype (ie people expect to hear it, therefore they hear it). There is a third possibility that only some are sensitive to this phenomenon.


SY said:
And the fourth possibility, that there are some components which can affect this (most notably speakers) and others that don't (e.g., amplifiers).

And a fifth possibility; that it has nothing to do with timing, but more to do with dynamic compression or perhaps slew rate, which may be perceived as a timing issue. If our perceptual system acts like a peak detector, and the leading edge of a peak is rounded, it's conceivable that we might interpret that peak as being delayed. Conceivable, I say. The problem with conjectures like this in audio (well, other more important things too), is that they quickly morph into received wisdom and are generalized over a wide range, like "this or that tube sounds good or bad".

Sheldon
 
I have some problems there with orders of magnitude. Timing in a musical sense is something that is of the order of 10ms or greater. Slew rates are about a thousand to ten thousand times faster. Same with the delays involved in transient response- they're a thousand to ten thousand times faster than anything that can upset musical timing.
 
SY said:
I have some problems there with orders of magnitude. Timing in a musical sense is something that is of the order of 10ms or greater. Slew rates are about a thousand to ten thousand times faster. Same with the delays involved in transient response- they're a thousand to ten thousand times faster than anything that can upset musical timing.

Can't dispute that SY, the slew rate comment was an afterthought (mostly after, short on the thought). I guess my primary notion was the possibility of some compression being perceived as a timing effect - also meant more as a question (well, idle speculation, actually). I can imagine that music with some relative compression might sound less "lively", and that might be interpreted as pace or timing. But in going from the subjective to physics one can't blithly ignore the number of zeros.

Sheldon
 
The dreaded 'prattle disease' appears to be highly contagious, and now appears to be affecting non-english speakers. Fabio Camorani (Positive Feedback Vol 1 - 'Kismet').

Have you ever tried to use small capacitors? The smaller they are, the better, but using this approach with a power supply may cause several problems. First is noise and poor energy, but with the new working point of the output tube, the current is lower and a smaller capacitor is required. Starting from this, I tried to lower the values of all anode power supply capacitors. With small values, the bass is faster and has more harmonics—in short, there is more music.

Beware ! if you suspect you may be succumbing to this condition seek medical attention immediately. Initial symptoms (especially among north Americans) may include sporadic use of the term 'boogie factor'.

Let's just pray this doesn't become a pandemic.
 
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