Tube Watts --vs-- Solid State Watts

jerry wallace · Post by **jerry wallace** » 3 Jul 2001 1:35 pm

CAN ANYONE TELL ME WHY IT SEEMS THAT A TUBE AMP RATED AT 50 OR 100 WATTS RMS, SEEMS TO HAVE AS MUCH OR MORE OUTPUT THAN A TRANSISTOR AMP RATED AT 200??
DOES A TUBE HAVE THE ABILITY TO RESPOND TO PEAKS FASTER THAN A TRANSISTOR AND THEREFOR THE ABILITY TO PRODUCE MORE OUTPUT AT THE SAME RMS WATTAGE??

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Jerry Wallace- "98 Zum: D-10,8+8, "96 Zum: D-10,8+5,Nashville 1000,Session 500 ,Session 400 head only amp,Tubefex,ProfexII, Artesia, New Mexico

C Dixon · Post by **C Dixon** » 3 Jul 2001 3:06 pm

Jerry,

Interesting question. And very poignant indeed. Here is the scoop. Transistors are "solid state" devices-tubes are "free space" devices!

Now what does that mean and how does this relate to power and your question? OK---Electrons flow faster thru free space than they do thru a sold device. In engineering "lore" it is called "transient time". Meaning it takes longer for electrons to flow thru a transistor than thru an equivalent tube.

Now how does this manifest itself. OK, power is ONLY one factor when a human perceives sound. The other is how fast a signal can change from low level to high level (and vice versa) sounds.

The best way to understand this is to try and capture the "crack" of a 22 rifle versus the sweet mellow tone of a violin bow accross the strings. Even though the violin might be playing thru a 200 watt amp wide open!!

Having a high powered amp is of little use IF that amp cannot go from "off" to full Power instantly. Tubes can do this for all practical purposes. Transistors have a problem with it.

Engineers new this from the get-go. And in the real early days, it was a joke indeed. When I was with RCA labs we could take a 25 watt tube stereo unit and have it perceived louder than a 500 watt solid state unit. Note, this was not faking the power as many advertisers did before the government clamped down on them. This was true RMS power.

Again it is called "transient time" in engineering books. It is called "dynamic range" by lessor than engineering books. In scientific and research labs it is called "rise time".

For all practical purposes, a tube's rise time is instantaneous whereas a transistor's rise time lags behind.

Good news though. IF you compare the very pitiful performance of the first Solid State amps to say a Peavey Nashville 400, they have come a long way. A very long way. True, any engineer will tell you that a transistor still can not completely duplicate a given tube's rise time. But they have made great strides. One day, who knows? They may come soo close as to be imperceptible.

Until that day, it will not be uncommon to feel a twin reverb has more power when some one picks a bass string versus doing it on an even more powerful solid state amp. Remember power and dynamic range are two different animals. It takes one heck of a fast device to duplicate the "crack" of a 22 rifle even at low volume. Or the plectrum sound of your 10th string on C6th thru an amp.

Hope this helps,

Carl

jerry wallace · Post by **jerry wallace** » 3 Jul 2001 5:21 pm

Hello Carl,I knew you could enlighten me on this topic..What you have said makes perfect since to me...While I have some limited knowledge about electronics,I am not at all an expert..but I and others have noticed that it seems to take 200 watts of SS power amps to do what 50 watts {2-6L6's} in a tube amp can do..Again I admire your ability to explain things so that even I can comprehend them....THANKS,,, Jerry

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Jerry Wallace- "98 Zum: D-10,8+8, "96 Zum: D-10,8+5,Nashville 1000,Session 500 ,Session 400 head only amp,Tubefex,ProfexII, Artesia, New Mexico

Olli Haavisto · Post by **Olli Haavisto** » 3 Jul 2001 11:56 pm

I remember that both "Guitar World" and "Guitar Player" tested the MosValve 2x80 version and they both compared it to similarily rated tube power amp and both found the MV to be "significantly louder".
Go figure...

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Olli Haavisto
Polar steeler
Finland

Jack Stoner · Post by **Jack Stoner** » 4 Jul 2001 2:31 am

I suspect most of the MosValve sound is in the preamp/driver section, not the power amp section.

Bill Crook · Post by **Bill Crook** » 4 Jul 2001 7:25 am

One must NOT forget that a tube amp has a much "warmer" sound than a SS amp. This is more due to transformer coupling than anything else. Because of the very shapeing of transformers,the signal is shaped like a bell curve as opposed to a sharp cutoff in SS devices. Tube transiences(and noises) also apply to the overall signal design. In the early beginning,Solid State devices were considered to be very harsh and non-pleaseing to the ear,(was even detectable by the novice person) but now advances in technology, has decreases the envelepoe of SS devices.

(Well, the wife saids "We need to go now") so I'll continue this later.

Jim Smith · Post by **Jim Smith** » 4 Jul 2001 10:37 am

I remember that my first Session 400 was way louder on 4 than the silver faced Twin Reverb I had been using was on 10. Both had 4 ohm 15" JBL's too. Whassup with that?

Donny Hinson · Post by **Donny Hinson** » 4 Jul 2001 2:12 pm

"Total amp power" is available only, and should be measured only, at full-volume. Different pot tapers can make quite a difference in the less-than-max settings. I almost always run any amp I use "wide open", and then control all the volume with the foot pedal. I get a more consistent sound (better tone, and more available dynamic range) that way.

jerry wallace · Post by **jerry wallace** » 4 Jul 2001 2:41 pm

Donny,do you run both or all, I guess I should say of the volumes/gains wide open?..By that I mean the pre , post, master or sensitivity or what ever else it maybe called on different amps??
But what I am asking is "Everything" wide open?
In studying the manuals on several amps,its my understanding that the volume /gain pots are only changing the input and output levels to the preamp board and NOT the gain of the power amp section in a amp..

So if I understand what you are saying,It fits with the only way the output power on most amps can be driven to max,is by increasing the preamp output which is the input to the power amp ..Hence, the actual "gain" of the power amp section is fixed..In order to get more out it has to have more in.. Right?? [This message was edited by jerry wallace on 04 July 2001 at 03:47 PM.][This message was edited by jerry wallace on 04 July 2001 at 03:48 PM.][This message was edited by jerry wallace on 04 July 2001 at 03:54 PM.]

Olli Haavisto · Post by **Olli Haavisto** » 4 Jul 2001 2:57 pm

The reviews I mentioned stated "significantly louder before clipping" which I think means that the compared amps were driven to their maximum clean output.

Tyler Macy · Post by **Tyler Macy** » 4 Jul 2001 9:58 pm

I think that for a solid state amp and a tube amp of the same wattage, the tube amp will have more "usable" wattage. That is, more of its available power will be useful. As a tube amp is pushed hard it distorts, but the human ear doesn't hear it as distortion (not at mild levels, anyhow). However, whenever a SS amp begins to clip, you know it, and it don't sound good at all. Therefore, for any given wattage, a tube amp is often perceived as being louder.

Tyler

Dan Tyack · Post by **Dan Tyack** » 5 Jul 2001 4:52 pm

My rule of thumb is that transistor power amps should be as powerful as possible (within practical limits) because transistor power amp distortion always sucks. Whereas tube power amps should only be as powerful as needed, because they start to sound great when driven.

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