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Thread: Tube amp question

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    Default Tube amp question

    I'm in the market for a new amp. I have always owned solid state amps so I know exactly how much power there is for a 30 watt, 50 watt, 100 watt amp when it comes to solid state.

    But With tube amps it seems a 30 watt amp is the equivalent of a 100 watt solid state. I've even seen tube amps advertising a powerful 5 watt.

    I realize there probably isn't a conversion chart but can someone set me straight on the difference of power between tubes and solid state?

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    Registered User Jeffff's Avatar
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    Default Re: Tube amp question

    It's not watts that are really important, it's decibels. I have a Fender Deluxe Reverb Reissue that's rated at 22 watts. It is so loud that I uses a THD hotplate in most cases.
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    Default Re: Tube amp question

    I'm not sure that what you're asking for really exists, in terms of direct conversion. I've had people using Fender Deluxes blow me off the stage when the dude with a Marshall stack sounds timid by comparison. For most of the bar shows I've played with an electric mandolin in a rock band I used a Fender Hot Rod Deluxe - 30 watts. I don't think I've ever had it above 6, and I can cut through all but the loudest drummers and guitar players. Wattage will make a real difference in terms of clean volume before tube distortion begins to creep in, this is referred to as "headroom." If you want to play clean and loud, you need a powerful amp, more so the higher your instrument's output. The Fender Twin seems to be the general benchmark for a loud, clean amp, it has headroom to spare for all the loudest players and situations. If you want natural distortion at low volume, you want a low-wattage amp, or at least a lowER wattage amp. As a side note, amps with ample headroom tend to handle pedals better, if that's something you want. Balancing those things is a question of experience and time. Good luck!

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    Work in Progress Ed Goist's Avatar
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    Default Re: Tube amp question

    As the volume of a SS amp increases, just the volume increases.

    As the volume of an all-tube amp increases, several other things also increase (compression, distortion, and sag). All of these other things also increase the "perceived loudness" of the amp by a very big factor. Moreover, with a tube amp you are experiencing uneven harmonics (even harmonics in addition to odd harmionics), and this also substantially contributes to the perceived loudness of a tube amp.

    So, even at the same measured decibels, a tube amp will seem louder to a listener.

    Of course the speakers and the speaker enclosures used will also dramatically impact the results.

    As a test of the difference between the perceived volume of tube vs. solid state I played a 19 watt all tube amplifier (based on a Fender Princeton) and a 75 watt Line 6 all solid-state amplifier through the same Celestion Custom Design 12" G12P-80 speaker (rated 8 ohms, 80W) mounted inside a Line 6 Spider combo amp. I tested at 1/4, 1/2, and 3/4 volume, and used me and my wife as the test subjects.

    To my ears, at about all the different volume settings these amps produced about the same loudness. However, when we got to 1/2 volume and above, my wife was certain that the 19W tube amp was louder.

    So, from my experience with this little test I'd say the difference is about 4+ to 1. (1 tube W = 4+ SS W).

    Finally, I should say that my current amp, the 15W Fender Super Champ XD (a hybrid) seems to fall in between on the loudness scale, but is closer to the all tube loudness profile (despite the fact that the Super Champ only has a 10" speaker).

    Of course, YMMV, and this is a heavily debated topic with equally qualified experts strongly disagreeing.
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    Default Re: Tube amp question

    In case you're not aware, one difference is that tube distortion tends to sound good (plus come in slowly and early) while solid state distortion tends to sound bad and happen all at once. When pushing either type toward and past its limit, the tubes will seem to sing right along (even if a mathematical analysis would say that there's lots of difference between the input and output signals) while the solid state will sound like a ton of bricks.

    My (way back!) rock playing was mostly with an all-tube 40-watt piggyback Fender Bandmaster (two 12s). Bass-heavy rhythm was usually played on 4, LOUD. Current amp is a partially-tube (and possibly hot-rodded) Champ 12 from the early '80s that I found in the early '90s (12-watts, one 12 speaker), still on either 3 or 4. Especially on the "drive" channel (that is, intentionally distorted), peak volume is WAY louder than I'll ever use.

    Yeah, there's no easy conversion... ya just gotta listen. Sortta like buying a new mandolin!
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    Default Re: Tube amp question

    Quote Originally Posted by Ed Goist View Post
    ... from my experience ... I'd say the difference is about 4+ to 1. (1 tube W = 4+ SS W).
    Good points Ed; I like your conclusion. (Hey, we were writing at the same time!)

    A related point (from my high-end audio freaks, er, friends) is that the perceived increase in volume is far less than proportional to the wattage in use. As best I remember, it pretty much boils down to:

    - A doubling of wattage equals 3 decibel increase in volume at the speaker. But, because of the vagaries of human hearing...
    - A perceived doubling of volume requires a 10 decibel increase at the speaker, and that requires a ten-fold increase of wattage!

    In roundish figures, let's assume we have a 10-watt amp. Double that to 20 watts for a 3db increase of volume, double it again to 40 for a 6db increase of volume, double it again to 80 watts for for a 9 db increase, then just nudge it up a notch (okay, by 25%) to 100 watts for the 10 db increase that we frail humans perceive as a doubling of volume.

    So a 100-watt amp is twice as loud as a 10-watt amp, not twice as loud as a 50-watt amp (ALL ELSE BEING EQUAL, and we know they never are!).

    Sort of explains why a 60-watt amp isn't all that different from its 40-watt sibling. Things like speaker efficiency (NOT its rated "handling power" that tells you nothing about volume, just how much electricity will blow it up) and cabinet design turn out to have far more impact than raw wattage does. Also sort of explains how the ol' '55 Chevy could blast the neighborhood with only a 3/4 watt monaural AM radio!
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    Default Re: Tube amp question

    Great points by Ed above.
    If one isn't playing out and in competition with other amplified instruments and drums, one really doesn't need a lot of watts to be quite loud.
    In the test I mentioned above, both amps were VERY loud in my practice room (maybe 15' X 12' X 8') even at 1/4 volume, and they were darn near uncomfortably loud at 1/2 volume and higher.
    Also, I have played through both a 15W/8" solid state Marshall combo, and the 5W/10" Marshall Class 5 all-tube combo at my local Guitar Center and thought that both were quite loud in the large GC showroom even at fairly low volume settings.
    IOW, like Ed points out above, it doesn't take much wattage to get loud.
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    Default Re: Tube amp question

    Lots of variables in the question, not even addressing the good points EdH makes about decibel/power/perceived loudness relations.

    With proper measurements held constant, e.g. % harmonic distortion, efficiency of speaker rig, type of instrument used, then watts are watts. (BTW, 30 is very conservative for the Hot Rod Deluxe, I think it's 2 6L6 power tubes, used to be called 40W)

    Tube combo amps are typically open-back and fairly efficient cabinets, making for a very live and present feel. Many solid-state amps try to be more hi-fi, running low-efficiency but more accurate speaker designs. (Like pretty much all the "acoustic" amps.)

    And, as pointed out above, tube distortion is generally palatable if playing a magnetic-pickup string instrument. But if one chooses solid-state designs that are intended for the same application, i.e. mag-pickup guitar playing into a guitar cabinet, you can get fine sounds. I am quite happy with the Electro-Harmonix amp-pedal, 44 Magnum. It is basically the same power as a 22W traditional Fender Deluxe, if run into a similar cabinet. And instead of weighing 20 lbs, at least, for the amp chassis alone, it weighs one pound. It overdrives very sweetly, if you use a sweet speaker. I used it for a trio gig with my 10-string (mag pickup), driving a 6.5 in. speaker in a small ported box. It is quite loud into a 12", could easily handle a stage gig in rock setting, with efficient speaker.

    But I am content with a Crate PowerBlock head, 75W and 4.5 lbs, for loud gigs. I don't depend on the amp for overdrive tone, instead using a King of Tone from AnalogMan. This is way better overdrive and crunch and just plain sweetness than I ever got from my Twin Reverb, although the Super I had in the 70s was ok. Then again, it weighed like a Boogie. Better you than me, I want to bike to work.

    And let's also note that 3dB is a definitely noticeable increase in a mix. Twice as loud is rarely necessary. The small differences have some impact.
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    Work in Progress Ed Goist's Avatar
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    Default Re: Tube amp question

    Tom, the more I go into demoing amps with open ears, the more I'm finding that fine distortion and tone is very possible without the "all mighty" pre-amp tube. As you have mentioned previously, things like high quality pedals and tight EQ controls on the instrument and amp help shape good tone considerably.

    Case in point, just listen to this 15W Marshall solid-state amp. (BTW, this is the amp that I recently demoed at GC, and it just blew me away!):

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    Default Re: Tube amp question

    [QUOTE=Ed Goist;1013814]... Case in point, just listen to this 15W Marshall solid-state amp. (BTW, this is the amp that I recently demoed at GC, and it just blew me away!):


    A Marshall has been on my short list. You may have helped me make up my mind.

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    Registered User Jeffff's Avatar
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    Default Re: Tube amp question

    I find that solid state distortion is not dynamic enough for me. The same thing that makes them great at "bedroom" volume makes them sound sterile to me.

    No matter how hard you pick or where you roll the guitar volume knob the sound doesn't change.
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    Default Re: Tube amp question

    I consider the tube amp as part of my instrument because when we play together we express and experience our character together.
    Electric amplifiers just do what they're told.
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    Default Re: Tube amp question

    Quote Originally Posted by Lee View Post
    I consider the tube amp as part of my instrument because when we play together we express and experience our character together.
    Electric amplifiers just do what they're told.
    I have teenage daughters. I'd REALLY like something to do what it's told!

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    Default Re: Tube amp question

    Here's an idea: Hughes & Kettner makes what's named the Tubeman. It has one EL-84 tube and it works as a tube powered pre-amp. It's conveniently built like a foot pedal with three channels that can be switched without clicks while playing. The Clean has just a volume knob. Lead has volume and gain, Crunch has volume, gain and voicing knobs. It can be plugged into an electric power amp. I have an older Tubeman and found it fascinating to use.
    (Sorry, I don't know how to post a website.)
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  15. #15

    Default Re: Tube amp question

    For marketing reasons some manufacturers take liberties with the term "Watts." Some are rated in RMS [Root-Mean-Square], others are called "program" others will be peak-to-peak, etc.

    Look for ratings in RMS. A 100 watt RMS SS amp will provide the same output/volume as 100 watt RMS tube amp.
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    Default Re: Tube amp question

    Don't forget the efficiency of the speaker. You can make an amp sound nearly twice as loud by changing to a more efficient speaker. Hence those amps mentioned with loudness changes. I have make a Deluxe Reverb have nearly twice the volume and clean volume at that simply be changing to a more efficient speaker. Look for something at least 90db rating for efficiency.
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    Default Re: Tube amp question

    Where's a good place to review different speakers' efficiency and tone?
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    Default Re: Tube amp question

    Tube amps. (Valves to us in the UK) are very dynamic in operation.They operate totally in Class "A" mode,drawing a continuous amount of power from the mains supply,where as class "B" (or class A/B) amps only draw the power they need at any point in time.To put it in a simplistic way,when the amp.needs to put out a lot of volume,a class "A" amp is 'ready to go',whereas a class "B" amp. has to 'think about it'. The Hi-Fi Power-amp.that i used to have (before i had to junk it because of lack of Sony spares),was a solid state class "A" amp.,& even though it was a lower powered amp.compared to the class "B" amp.i use now,it could turn my current one inside out as far as dynamics go - Tube amps are terrific !,
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    Default Re: Tube amp question

    Quote Originally Posted by Lee View Post
    Where's a good place to review different speakers' efficiency and tone?
    Look at the spec sheet and look for efficiency. If it's not there contact the company and they should be able to tell you.
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    Default Re: Tube amp question

    I bought a new Twin Reverb in the 70s and asked for the version with JBL 12" speakers. That was incredibly efficient and therefore loud, but I tired of the weight of the JBLs and their uninteresting tone, too smooth, too hi-fi in the highs, which made any overdrive very crackly, like what we expected a solid-state amp to sound. I replaced them with the Fender/Jensen 12s, darker and warmer. Less efficient, one could actually push the amp into some overdrive without being as loud (still really loud, though).

    US Speaker sells many brands and has full data on most of them, including all the stuff like efficiency, resonant frequency, etc. I just bought a little Eminence woofer and used the info to pre-design a cabinet for it. They carry Jensen, along with Electro-Voice, JBL, and so on.

    Celestion (Marshall and many new Fender amps) has data on their web page. I like their 12" speakers, and they offer some 10 and 8 inch speakers, too. For tone, you may prefer a chart that shows a spiky curve, lots of little resonances. This will sound more musical for electric guitars, although too "colored" for acoustic reproduction. A curve with a dip in the range from around 800 Hz to 1600 Hz will sound sweet, while one with a bump there will have a hard, midrangy tone. The high end of Jensens is a peak at 2K Hz, but Celestions, rather brighter, peak a bit above 3K.

    I don't really like anything smaller than 12 for guitar, but 10s can be really nice for mandolin.
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