What is signal path INSIDE a tube amp ?

[Coytee]

Im still trying to cogitate the nuances of how a tube amp works.

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Pardon any specifics I butcher, Im just trying to get a basic understanding here.

The signal enters the tube amp. I presume the signal passes through the little tube for a basic step up in signal strength. From there I presume it goes to the actual tube (2A3, KT88, other) which does what ever it does (further step up?)

(here is the part Im really trying to figure out)

The signal then leaves the 2A3 and goes to the TRANSFORMER!!

So THIS (transformer) is where the punch that we hear really occurs, as the signal BEFORE the transformers would not be sufficient to create the sound which we hear.

Ok, so if that basic premise is true (is it?) then is it also fair to say that in addition to what ever the sound characteristics a 2A3 might have inherent to its makeup, the transformer will ALSO have a significant effect on the sound we hear. Indeed, perhaps more of an effect.

If the above generality is correct, then how might one evaluate different transformers and are there different types of transformers that will have inherently different sound? (yet similar within same type)

Are there certain brands (or types) that are the brand to use?

I presume you can undersize a transformer, so can you put a MONSTER transformer on a regular sized amp and have it work great? Or perhaps, like a carburetor on a car, you size the carb to the engine size, cam, work intended? Anything above a certain flow rate is simply wasted/unusable flow for that engine size?

If you size it to the job, what are the parameters you consider when matching?

[Nklipsch]

The tube is an amplifying device,it does the same job as a transistor but in a different manner. The output transformer couples the signal to the loudspeaker more efficiently.Note that the output transformer isnt perfect and will impart some sort of distortion onto the output waveform(which is why they can cost alot)

A tube guy can reply in more detail

[3dzapper]

"The signal then leaves the 2A3 and goes to the TRANSFORMER!!

So THIS (transformer) is where the punch that we hear really occurs, as the signal BEFORE the transformers would not be sufficient to create the sound which we hear."

Let's look at this part.

The 2A3 is a voltage amplifier. It may take say a +/-20 Volt swing at it's input (signal) grid and convert this to 200V. This is where the "punch" comes in. I wouldn't want 200V at my speaker outputs so I put a transformer in that steps the high voltage, low current output from the 2A3 into a low voltage high current that my speakers can use. There are other considerations to consider like the inpedance "seen" by the tube and the output to consider also.

The choice of transformer will have a large effect on sound quality as well as the type of transformer used. Some SET transformers have an "air gap" built in. This helps prevent the tranny from overheating due to the constant current of the class A design. It also will affect the tone. Others have what is called "parafeed". Using this topology the windings can be more closely coupled reducing losses.

Rick

[dragonfyr]

Check out this site. There is ALOT of stuff here, but there are also some tutorials that step you through classic circuit configurations. I hope that this might be of help.

http://www.tubecad.com/

And to really confuse things, be aware that there are MANY different (tube) topologies, each with their advantages and disadvantages!

And YES! Transformers effect the sound as well!

Check out the following for a simple overview of transformers:

http://www.sescom.com/audio/transfor_tech_issues.html

[Nklipsch]

As far as I know,a transformer that is measured to be linear,will infact sound more linear. The issue is,people dont always want a linear system. (frequency response and distortion measurements)

?? http://www.elektor-electronics.co.uk/Default.aspx?tabid=28&art=50483

[Coytee]

I seem to recall some basic thing from shop class (decades ago) about step up / step down transformers...

As I recall, you had X volts and Y amps entering the transformer. It would step UP the volts (or down) and at the same time step DOWN (or up) the amps. I guess this is how our high tension wires work to a degree, then at the receiving end, there's a step down transfomer that lowers the volts but increases the amps (as per the power lines).

Sooooooooo, the tube actually creats high volts and low amps, the amps are what really drive the speaker so you need a step down transformer to lower the voltage and up the amps.

Did I butcher it, or do I at least have the cat by the tail?

If the above is reasonable, then the "little" tubes (I think they're called rectifier?) much like converting ac to dc, do just that? they convert the a/c signal to dc? and then this is what is stepped up by the power tube in voltage, only to be transformed from high volts, little current, to low volts, high current by the transformer?

If that's so, are we just taking a line voltage (low volts & low amps), converting it to dc (rectifier tube), stepping up the signal (now high volts, low current / power tube), and then transforming that to low voltage (again), BUT at this time, we have the magical high current to drive our speakers (transformer)??

So, we've taken a low volt, low amp signal, upped it by some factor, and then reconfigured the signal such that we end up with high amps?

[Coytee]

I think I was redundant

[JJkizak]

Think of the tube as a kind of control device, there is a large DC current flowing from cathode through the grid to the plate. Put a small AC fluctuation on the grid and it causes a huge perfect copy of the fluctuation at the plate which is AC which then can be coupled off with a capacitor to another circuit or the plate circuit current passses thru a transformer winding and the transformer only passes (couples AC components. So your controlling a huge DC current (electron stream) with a tiny small AC voltage. Bam! Now you have a big *** signal with lots of power. The problem with tubes is even though when they made billions of them you had to go thru about 10 of them to get one good one. Tubes have their own little nuances, they generate noise, they amplify the 60 hz filament voltage (known as hum)they get gassy and generate intermodulation distortion, they degrade rather profusely, they can become microphonic, they must be balanced, they run hot and must be fan cooled, they consume lots of power, they require huge components in their circuits, (not all) and if you drop an amplifier on your foot your in hurt city.

JJK

[Nklipsch]

As I recall, you had X volts and Y amps entering the transformer. It would step UP the volts (or down) and at the same time step DOWN (or up) the amps. I guess this is how our high tension wires work to a degree, then at the receiving end, there's a step down transfomer that lowers the volts but increases the amps (as per the power lines).

Your correct with the transformer idea.Power input/output are almost equal(some slight losses occur),all that changes is the ratio of V to I,energy is converted not destroyed.

Rectifiers ie Diodes 'chop' half the AC wave off,as they can only pass current in one direction,leaving you DC,of sorts.

Note that transistor amplifiers dont require output transformers as they have the right output for loudspeakers.

[D-MAN]

A tube or transistor is a SWITCHING device used to modulate current flow from the power supply. It does NOT accomplish any amplification on its own in the literal sense.

The APPARENT amplification comes from the POWER SUPPLY having a larger amount of voltage+current available in an available reservoir, which is "released" in relation to a modulating signal fed to the switching unit(s) (the PS attempts to maintain a consistant "quantity" of v+I at all times). For a triode (the basic 3-part tube), the input source signal is applied to the grid which modulates the flow of current from the cathode to the plate, depending on the polarity and amplitude of the input signal applied on the grid. The cathode has the entire PS reservoir of voltage+current available on it but is controlled by the signal on the grid circuit.

The OUTPUT TRANSFORMER is used to match the large-signal output from the TUBE/TRANSISTOR plate (don't remember the term for the transister part) to the impedance of the speaker.

DM

[Nklipsch]

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On 5/17/2005 7:07:44 PM D-MAN wrote:

A tube or transistor is a SWITCHING device used to modulate current flow from the power supply. It does NOT accomplish any amplification on its own in the literal sense.

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Indeed,thats a better explanation!Energy cant just appear

[Coytee]

Something is deeply bothering me...

I think I'm following some of this logic

[Marvel]

Tube Cad Journal. This is excellent, and you can most of the stuff online. Some is posted as PDFs, so you can save them, print them out and place in a notebook for reference. Like late at night when you want to read something before you fall asleep...

http://www.tubecad.com/

Mostly guitar amp related, but this has some great info and explanations:

http://geofex.com/tubeampfaq/taffram.htm

Link on the tube depot's website explans bias pretty well:

http://www.tubedepot.com/whisbipo.html

[mike stehr]

"The problem with tubes is even though when they made billions of them you had to go thru about 10 of them to get one good one."

Maybe with some samples, not all.

Tubes have their own little nuances, they generate noise, they amplify the 60 hz filament voltage (known as hum)they get gassy and generate intermodulation distortion, they degrade rather profusely, they can become microphonic, they must be balanced, they run hot and must be fan cooled, they consume lots of power, they require huge components in their circuits, (not all) and if you drop an amplifier on your foot your in hurt city."

Gimme a break.......

[Nklipsch]

Listing the negatives of only one device is like hearing only half the story(or even quarter)of the story.

[scriven]

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On 5/17/2005 6:59:04 PM JJKIZAK wrote:

... Tubes have their own little nuances, they generate noise, they amplify the 60 hz filament voltage (known as hum)they get gassy and generate intermodulation distortion, they degrade rather profusely, they can become microphonic, they must be balanced, they run hot and must be fan cooled, they consume lots of power, they require huge components in their circuits, (not all) and if you drop an amplifier on your foot your in hurt city.

JJK

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I'm guessing that he is not one of the many tube enthusiasts on this forum.

[mike stehr]

He does make a point, they can be a PITA......

[Coytee]

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On 5/17/2005 7:53:09 PM Marvel wrote:

. Like late at night when you want to read something before you fall asleep...

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Would right now qualify? or would this be considered early in the morning? (note timestamp)

Darn Chloe (dog), she loves to lay next to me and lick me until I awake

[Mark Hardy]

I probably shouldn't bring this up, but:

I am having a little philosophical trouble with the statement that tubes and transistors are switching devices. It's not untrue, and of course the earliest digital computers used tubes (lots of them) as switches to make logic gates. But I think the best analogy for the way a tube uses the signal at a grid to control the flow of electrons between the plate to the cathode is as a "valve". It's no secret that the old school term for a vacuum tube is valve (still so-called in the UK and Europe). Indeed, to this day, on schematics, tubes are identified as "V1, V2" (Valve 1, Valve 2), etc.

The concept of a switch, though not inaccurate, just seems a little too quantized for me to think about the use of a vacuum tube as an analog signal amplifier.

Sorry for the interjection.

[D-MAN]

It is technically regarded as a electronic switching device, tubes being voltage driven, transistors being current driven.

The usage depends on the circuit type it is used in.

Do not regard the use of the term "switch" to mean on-or-off only, which is what I think you are implying.

The nature of the current flow through the device is entirely dependent on the type of circuit that the device is employed in. The nature of the devices themselves does not change, but their usage does based on the circuitry.

DM