# Amp wattage



## RIFF WRATH (Jan 22, 2007)

can someone explain/clarify guitar amp watts to me.
(kindly note my avatar as "student")
I am reading and seeing low wattage amps/heads.
I have always been under the impression that 150watts + was a desired wattage. How does a low watt amp drive a cab? What is the proper way ,for instance, to increase output from a 15 watt practise amp?
thanks for your patience.
cheers
Riff Wrath


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## Jeff Flowerday (Jan 23, 2006)

Solid state absolutely. When it comes to solid state you need way more power to translate that into DBs. That said not many use solid state when it comes to a guitar amplifier.

Tube power is a different thing. 18 watts is more than I ever use. 30 watts with an efficient cab will be more than powerful enough to keep up with any drummer in pretty much any venue.

Not to say more watts isn't ever needed. You may need more if you need more clean headroom.

This is my take on it, anyway. I hope it helps.


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## Bevo (Nov 24, 2006)

Knock planes out of the sky...I love that!!

Let me give it to you in Laymans terms..Fellows, feel free to correct.

There are two types of amps, one solid state and the other tube.
A 50 Watt Solid state amp at full volume is not as loud as a 50 watt tube. The reason is in the components that make up the amp section. 

Amps are generaly unable to increase output wattage except in the Tube style. A good tech can change tubes and output transformers to increase the output, solid state you are kinda stuck.

Amps also come in two different styles, the Head and the Combo. Head is amp only and combo has the amp built into the speaker cabinate like your practice amp.
Some Combo amps do come with an output jack so you can run a external cabinate with or without the original speaker.
Heads can run anything as long as the Ohm ratings meets up, if they don't then it can hurt the amp.
A 5 Watt amp can run a 4X12 cabinate but not very loud, a 50 can run a 1X12 but good luck getting the volume past one..if you do watch out for the planes falling. 
My 50 Watt solid state Line 6 at 5 is not as loud as my 15 Watt Traynor Tube amp at 5.

Idealy you want an amp that #1 has the tone you love, if you are just learning then go with a modeling amp..this way you can get any sound out of it without buying pedals ( pedals change the output sound of the amp).
Wattage is relative to what you are doing, bedroom playing keep it under 15 or even 5 Watts. Band stuff depends on how much you want to spend, tube amps tend to be much more expensive than solid state but are worth it for the tones.

Hope that helps, if you want to get more technical there are guys here that can easily help you out.
Bev


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## dwagar (Mar 6, 2006)

here you go:










That'd be Clapton behind Steve Winwood, 2 100 watt Marshall stacks. The Hyde Park concert, outdoors, over 100,000 people. 

That's when you need to get into that 150-200 watt tube amp range. (course, they didn't have the monster PAs to mic everything through back then)


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## Scottone (Feb 10, 2006)

Bevo said:


> Knock planes out of the sky...I love that!!
> 
> "Let me give it to you in Laymans terms..Fellows, feel free to correct."


Since you asked....


Bevo said:


> "There are two types of amps, one solid state and the other tube.
> A 50 Watt Solid state amp at full volume is not as loud as a 50 watt tube. The reason is in the components that make up the amp section. "


a watt is a watt, doesn't matter if it is tube or solid state. Many tube amps actually put out considerably more wattage that their rating though (i.e. a 100 watt Marshall may actually put out 175 watts fully cranked), which may be the genesis of this widely held belief. Come to think of it, the different damping factor between tube and solid state output stages may be something to do with it too. 



Bevo said:


> "Amps are generaly unable to increase output wattage except in the Tube style. A good tech can change tubes and output transformers to increase the output, solid state you are kinda stuck."


may also need to change the power tranformer in this scenario as well since you'll often need to increase the B+ voltage. Once could also mod a transistor amp to increase wattage if they really wanted to.



Bevo said:


> "Heads can run anything as long as the Ohm ratings meets up, if they don't then it can hurt the amp."


slight impedance mismatches won't hurt the amp, and may sound good.



Bevo said:


> A 5 Watt amp can run a 4X12 cabinate but not very loud, a 50 can run a 1X12 but good luck getting the volume past one..if you do watch out for the planes falling.


A 5 watt amp through an efficient 4x12 can get pretty damn loud. 1x12 cabs are generally no more efficient than other cabs. I run my 30 watt Stephenson through a 1x12 cab and turn it up way past 1.

Riff, what kind of music are you playing? That will be a big factor in your power requirements.


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## Coustfan'01 (Sep 27, 2006)

Contrary to what a lot of people will say , solid state is not necesserely bad . I love my vetta 2 , and I've never seen a more versatile amp...It's as expensive as almost any tube amp though .

And about wattage , like the other guy said , it's because the amps are rated in watt at a certain (low) thd . Past that , either the ss amp has all controls at 10 ( crates are rated that way ) or either it will clip ( which sounds really bad ) , while a tube amp will start having a hearable power amp distortion , which is pleasing to the ear . So you may have a 100 watts clean or almost clean , and 150-175 watt with a lot of distortion , while on a ss amp you have 100 watt on distortion , and equal or less clean .


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## Wild Bill (May 3, 2006)

*"Warning! Long Wild Bill techie post!"*



Coustfan'01 said:


> Contrary to what a lot of people will say , solid state is not necesserely bad . I love my vetta 2 , and I've never seen a more versatile amp...It's as expensive as almost any tube amp though .
> 
> And about wattage , like the other guy said , it's because the amps are rated in watt at a certain (low) thd . Past that , either the ss amp has all controls at 10 ( crates are rated that way ) or either it will clip ( which sounds really bad ) , while a tube amp will start having a hearable power amp distortion , which is pleasing to the ear . So you may have a 100 watts clean or almost clean , and 150-175 watt with a lot of distortion , while on a ss amp you have 100 watt on distortion , and equal or less clean .


There is a phenomenon called "psychoacoustics", referring to how due to the peculiarities of the human ear we perceive sound in a different manner than one would expect from common sense.

To us a sound needs to be 4 times louder to be perceived as twice as loud. This means 1 watt, 4 watts, 16, 64 and so on. This is why a 5 watt Champ into a 4-12 cab sounds pretty loud. It's not as many steps as you'd think below a 50 watt Plexi! Audio volume controls are tapered inside to change NOT at a 1,2,3 linear rate like with a motor speed control but rather at the 1,4,16 rate to match the human ear. This is called a "log" for logarithmic or more commonly an "audio" taper.

Amp voicing is also a psychoacoustic property. Bright amps sound louder for the same watts. That's why a VOX AC 30 at 30 watts will often cut through and over a 50 watt Bassman. It's why many amps have "bright" switches to leak more highs into the signal at lower volume settings. Our ears need more treble power at lower volumes to sound the same as at high volumes.

Our ears do indeed need much more power from a solid state amp to sound the same as an equivalent tube unit. As has been already said, we usually measure amp power before clipping. Solid state devices tend to stay clean until they are maxed out and then break into a harsh distortion. Tube amps have a long ramp on the distortion curve, where they just start to get warmer and "thicker". There's a long way past clipping before the distortion gets to be too much for most tastes.

Because of this the rule of thumb over the years for power difference between a tube and a solid state amp is actually 2-3 times! Remember, we're not talking about techie measurement differences here but rather the perception of our ears. So a 50 watt tube Plexi will honk nicely over a 100 watt ValveState. You'd need the 200 watt model to be sure of sounding louder and maybe not even then, depending on how bright a tone you dialed in.

You can google up a lot of techie papers on psychoacoustics that explain this better than I have but suffice to say, it's true! Techs first began to understand the differences between tubes and transistors when transistor mixing boards first started appearing in studios. The engineers immediately found they had to pad the hell outta the inputs when miking a source with high peaks and dynamics, like a singer who belts it out or a snappy snare drum. What was happening was that although transistors do a better and cheaper job with clean signals when you drive them hard they stay clean until they "lose it" and snap into harsh sounding clipping. The transistor inputs just couldn't handle the same peaks coming in as when using tubes.

This is why so many artists prefer tube studios and pay big bucks on Ebay for old tube Altec studio gear. It's not really that the tubes stay clean but that transistors would give a touch of harsh clipping on those peaks where the tubes masked the clipping. The clipping might still be there but the tube didn't hard clip but rather compressed and rounded off the "peak" so that the note sounded "warmer" instead of harsh. For years no one had really noticed or complained about this soft and warm clipping but with transistors the clipping was more painfully obvious.

You don't need a completely tube studio to appreciate the warmth of tube recording. All of these clipping differences occur in the 1st amplifying stage. A good tube preamp is all you need. Once the signal is amplified up to line levels in the board it doesn't matter if it's tube, IC or transistor.

Psychoacoustics is a classic case of where usually engineers just don't get what musicians are telling them. Engineers are schooled to think that a good amplifier is supposed to be as clean and "hifi" as possible. They jumped on transistors for audio like a fat lady on a doughnut! Yet the first transistor amps tended to go over like a lead balloon, except for bass guitar units. The reason was that unlike with bass guitar where you usually want an amp to be loud, clean and "snappy" a lead guitar amp is SUPPOSED to be distorted! Who the heck wants a hifi guitar amp? When the musicians complained the amp was too clean the engineers thought the solution was to add "fuzz", which of course was even more horrible.

The kind of distortion was the most important factor. Marshal spent years trying to get transistor circuits to sound like a tube amp. Yet today if you pick up a guitar player mag and do some counting you'll find of all the amps in the ads 75% at least will be tube amps and the rest will claim they sound like a tube amp!

I'm not saying it's impossible to make transistors sound like tubes but it still seems to require so much more complicated circuitry that you might wonder why anyone bothers. The reason is simple: MONEY!

It's much cheaper to make transistor amps! Of course, the savings were never to be passed on to the player in the retail price. The money seemed to stay in the manufacturer's pocket! Nowadays the price of electronic components suitable for tube circuits has escalated a lot due to much smaller production volumes than mainstream electronic parts. This pumps up the price of a tube amp. Still, players don't seem to care. Who wants a cheaper amp if it sounds like "ass"?


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## amphead (Jan 9, 2007)

The relationship between power and volume is not linear. Doubling the power of an amp only increases the volume it can produce by 3 dB (using the same speaker(s)), which is the smallest volume increase a human can detect. 

So, going from, say, 18 watts to 36 watts doesn't get you a real volume increase, but the amp will perform differently. In the case of a Marshall-like EL84 tubed, 18 watter, just adding another pair of EL84s to get to 36 watts gets you more clean headroom - not an increase in volume.

Increasing the power of an amp is more complicated than just replacing tubes, OT and increasing the supply voltage to the power tubes (B+). If an amp has been designed to accept a particular type of tube and you want to replace them with higher powered tubes the rest of the amp has to be considered at least as far back in the signal chain as the phase inverter. 

For example, output power would be increased by changing from 6V6s to 6L6s or EL34s. Or, moving from EL84s to those same tubes (you could go to 6V6s, but the power increase is not that much - changing from El84s to anything else will also require a tube socket change as EL84s are 9 pin tubes and the rest are 8 pin). Or you could go from 6L6s/EL34s to KT88s if you really wanted to boost the power.


To do that the PI's drive capability will likely have to be increased to give the new power tubes a bigger signal to take advantage of their higher power handling capability. Screen resistors should be looked at, the bias circuit might require changes and so on. This kind of change, IMO, requires a fairly major rebuild of the amp. I also think it's not worth it. By the time you pay a tech to redesign and rebuild your amp you could buy a new one!

Practically, the power you require is a function of the type of music you play, how much clean headroom you need, your band's stage volume and the size and type of venue you play. I know guys who gig with un-mic'ed 18 watt amps - they are very loud - in small to medium sized venues. They still use their 18 watt amps in large venues because they are always mic'ed. 

There are other things to consider such as whether you are after preamp or power amp distortion and the efficiency of the speakers. This post is long enough already, if you're interested I can give you my thoughts on these other things.

Hope this help!


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## RIFF WRATH (Jan 22, 2007)

Wow
thanks for the responses.all info good.

RE: music I play; I don't play yet.Going to try Bass (soon)

My preference in music is very broad but would fall under "Classic Rock"
I have been acquiring equipment for the past couple of years, mainly for the benefit of my musician friends. Unfortunetly they may play well but they can't answer my questions.Yes, they use my stuff.

Currently I have a 15W solid state Fender practice amp
10W ss Trainer bass practice amp
30W National tube amp cab (in for repair) with 2 8" speakers 
Line 6 120W ss 2X12 modelling amp.
5W epiphone ss battery practice amp
"no name" old tube amp (works) with mike hookup?

I guess my next question would be: the 30W National tube will be as good as new when I get it back (I hope, I hope), so, just use as is or? (I know, NOT for BASS)

cheers RIFF WRATH


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## amphead (Jan 9, 2007)

What model National is it? That's likely a real treasure. 30 watts will give you enough power to play in medium to larger venues. To maximize volume you may want to think about other speakers, but the National should be a great gigging amp volume wise. If it gets the desired tone you've got a great amp there.


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## Wild Bill (May 3, 2006)

*"I know! Picky, picky, picky..."*



amphead said:


> To do that the PI's drive capability will likely have to be increased to give the new power tubes a bigger signal to take advantage of their higher power handling capability. Screen resistors should be looked at, the bias circuit might require changes and so on. This kind of change, IMO, requires a fairly major rebuild of the amp. I also think it's not worth it. By the time you pay a tech to redesign and rebuild your amp you could buy a new one!


Not meaning to get picky but usually the PI has more than enough signal swing to drive any type of output tube. And usually there are similarities. EL34's and EL84's are similar in that they need less peak to peak driving voltage to reach full output than 6L6's. Whatever, pretty well any guitar amp preamp PI, particularly a longtail will have bags of drive.

As for driving power, it doesn't matter. The output tubes don't sink any driving power. By definition, in class AB1 there's no grid current and so no grid power drawn. The PI can in theory supply any number of output tubes, since it only has to deliver voltage. 

Some old SVT's and similar amps ran class AB2, which of course does require driving power to the grids. Of course, if its an AB2 amp it's likely so damn loud nobody's gonna soup it up anyway!

I've found it's rarely cost effective to try to get more power out of an amp. As Mr. Amphead has already said, you have to beef up everything else in the amp to handle it and by the time you've finished it would have been cheaper to have started with a bigger amp anyway. Hotrodding can actually blow things up. The classic example is old Sears Silvertone amps. Guys who have learned just enough theory to be dangerous notice that the amp runs the screen voltages on the tubes much lower than the plate voltage. It seems easy to just bump the voltage up on the screens but the output and power transformers were never asked to be strong enough to handle that kind of power. So when they finished that Silvertone amp, instead of getting only 30 watts from a pair of 6L6's they got the full 50 watts such a pair would normally deliver.

For about an hour, maybe. Till the trannies burned out!


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## Scottone (Feb 10, 2006)

Wild Bill said:


> For about an hour, maybe. Till the trannies burned out!


Probably sounded killer for 59 minutes and 59 seconds though :rockon2:


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## RIFF WRATH (Jan 22, 2007)

*wattage*

Amphead
you inquired about the national amp

I started a thread on it Jan.30, with some views but no responses.

I still can't comprehend that a small in stature tube amp can apparently kick butt.
i can't wait to get it back and I have a 90's japan Strat that I can try it out with.( I can't play yet but with the Line 6 on Insane and the stat plugged in I can make awsome Jimi noises)

cheers
Gerry


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## Lemmy Hangslong (May 11, 2006)

A 50 watt amp is not half as loud as a 100 watt amp... it's half the rating yes but a 10 watt amp is percieved by the ear as half as loud. A 1 watt amp is quarter as loud. A 50 watt amp is very close to three quarters as loud.
A decibel is a logorithmic unit and a 3 decibel increase doubles the strenth in volumn as percieved by the ear.

If I run my 50 watt head into a it's load break at 2% thats 1/2 awatt. One would expect that to be very quiet... it's not... it's still pretty loud... a raised voice that is not straining is required to talk above it.

Khing


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## amphead (Jan 9, 2007)

The PI has to be designed to provide a voltage signal that works with the amplification factor of the tubes it is driving. EL84s have a higher amplification factor - gain - than, say, 6V6s and EL34s. Therefore, the PI tail resistor (assuming a long tailed pair PI topology) has to be adjusted to provide a larger voltage swing at the PI output when using 6V6s as compated to EL84s. So, depending on which tubes you are switching to, the PI needs tweaking. 

I guess my earlier post was unclear - I was pointing out the possibility of having to make adjustments to the PI when changing power tubes relative to the PI's ability to provide the right voltage swing at its output.

Regarding sound levels, it is important to know that a 3 dB increase in volume is an almost imperceptible increase to the human ear. 

"Under controlled conditions, in an acoustical laboratory, the trained healthy human ear is able to discern changes in sound levels of 1 dB, when exposed to steady, single frequency ("pure tone") signals in the mid-frequency range. It is widely accepted that the average healthy ear, however, can barely perceive noise level changes of 3 dB."

A 10 dB increase in volume is perceived as being twice as loud - and this requires a 10X increase in output power as KHINGPYNN pointed out.

Regardless of the detail, RIFF WRATH I bet your refurbished National is going to sound great. Can't wait to hear your feedback!


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