what does it take to double wattage?

[ninjadave7]

I am learning about amps and was curious what it takes to double the wattage on an amp? I have been learning on a Goodsell Super17, and comparing that schematic to the Goodsell Custom33 the only difference (besides a choke) seems to be 4xEL84's instead of 2xEL84's in the 17w amp. I would guess the OT is different too? But not sure. So, is it (basically) as simple as adding a couple power tubes?

[diagrammatiks]

you'll need a power transformer capable of supply more current in both the b+ supply and the heater supply.

to go from 2 el84s to 4 el84s requires an additional 1.5A of current at the least. You'd also require 50-100ma more current on the b+ line.

the output transformer has to be specced to a different primary impedance and capable of handling more output...which means it has to be tapped at different places and bigger.

[Enzo]

Remember, your tubes don't MAKE power, they merely control the existing power from the power supply. That is why the term "valve" is used for them in many parts of the world. Valve really is a better description for them.

As diag said above, you'd need a heavier power supply, more current and probably higher voltage. The output transformer would indeed need changing, since the impedance of 2 tubes is different from 4 tubes.

And lest you think it will be twice as loud or something, it won't doubling the power will get you only 3db louder.

[R.G.]

Absolutely correct again Enzo.

I keep telling people that they ought to think of power amps as a small bump on the power supply that lets a little of the power out under controlled circumstances. No bigger power supply, no bigger output power, no matter what else you do.

[soundguruman]

If you double the wattage, it won't be that much louder. It takes several times the power to increase the loudness to a noticeable degree.

[MWJB]

Whilst it may be true that tubes do not "make" power and that if your current PT & power supply will not support the Wattage you seek (they would not appear to in the OP's case), you will never make it. However, it can be perfectly feasible to double or in some cases cases triple power in amps with an over designed power supply. This possibility needs to be assessed before any decision is made.

Think about a Champ, specifically a SF Vibrochamp, change the OT, rewire a couple of sockets, upgrade the speaker and your 6W amp is now pushing 18W+ in fixed bias.

There are plenty of 40-50W amps with PTs that have capacity for 5 or 6A of heater load and enough current reservoir to make 80-100W RMS.

Yes, an amp may be limited by the power supply, but the tubes do liberate that power...in the same way that putting a bigger gas tank on a 50cc moped won't make it a 100cc motorcycle. The extra 50cc doesn't "make" power either, the higher BMEP merely better exploits the energy stored in the fuel tank ;-). Subbing a 50W power transformer for a 100W item, that runs the same B+ voltage will not increase a 50W amp to 100W...you need the tubes to accomplish that.

Two amps of the same measured wattage can perform at vastly differing volumes, one 50W amp can be twice as loud as another. Loudess is not measured in Watts, but in dB. It may be true that if the ONLY thing that is different, is the measured wattage (same speaker efficiency, same sq. inches of air pushed by the speakers, same B+ & type of tubes, same method of bias), then a 100W amp may be "just noticably" louder than a 50W, but in reality amps are not typically built like that. The 3dB rule is a valid notion, but in reality a pretty abstract concept.

[soundguruman]

A good example is these amps with the 60/100 watt switch on the back...
you change from 60 to 100 watts or the other way, and it makes only a barely perceptible change in loudness.
Same between a 100 and 50 watt amp, very little difference in volume.
To the human ear it takes 10 times the power to double the volume. But you are in luck, because a good speaker
will also double the volume, without increasing the power at all.
So I think you may really want a really good speaker to make it louder, even though you may not realize it.

[MWJB]

"To the human ear it takes 10 times the power to double the volume." Indeed, but only when all other factors remain equal.

Remind me, who makes that 50W amp that runs 10x6V6s single ended, cathode biased, with 10x 8" speakers? ;-)

[Gibsonman63]

The easiest fix for more volume would be a more efficient speaker, a bigger speaker or more speakers. If I am not mistaken, double the power equals an increase of 3dB. Unless you already have a very efficient speaker, you can probably find one that's at least 2dB louder.

[soundguruman]

Exacto, if you increase the power enough to get a 3 db increase in loudness, that's a lot of power,
but you can get that increase just by changing the speaker, and skip the amp modification.

[Chuck H]

To the human ear it takes 10 times the power to double the volume. But you are in luck, because a good speaker
will also double the volume, without increasing the power at all.

I think your going to have to prove that.

Most stock speakers aren't the most efficient. A 3dB more efficient speaker is usually easy to find. This would be like doubling your WATTAGE which is not the same as doubling your volume. Often you can find a speaker 4dB more efficient. The volume increase is huge, but not double.

[soundguruman]

Eminence Legend 1218 = 98.8 db 1 W 1 M
EVM12L= 100db 1W 1M
Celestion Rocket 50 12”= 95 db 1W 1M
(typical of stock speaker in many amps)
Peavey Sheffield 12” 97.8db 1W 1M
(typical of stock speaker in many amps)
JBL 2020H 12”= 103db 1W 1M
Jensen Alnico 12”= 95db 1W 1M
(typical of stock speaker in many amps)
However, the efficiency of many stock speakers is so low, they are not rated. And a lot of manufacturers may not be truthful about the SPL tests.
And of course the enclosure makes a pretty big difference too.

the way I do it, the diff between Jensen and EVM could be 5 db on 1 watt. But not everyone wants a 27 pound speaker. I love it..

If you are willing to build the recommended cabinet, you can do better than 5 db.

[MWJB]

People usually choose speakers for their tone, SPL is a secondary concern...as long as the amp is working well enough.

[Chuck H]

Right, I did mention that many stock speakers are not the highest efficiency. Now I had no idea the Celestion Rocket 50 or the Jensen (alnico?) has an SPL of only 95. That is terrible. Most efficient speakers don't break 101dB. Considering that you'll probably want to choose the speaker for it's tone as well it's less likely that your going to get one of the smaller number of models that are higher than 101dB. Also, I wouldn't consider cabinet construction part of changing speakers. That's changing cabinets. Just the same, if you had a Celestion Rocket 50 (95dB?) and you replaced it with, say, an Eminence Wizard (104dB) AND used a special design cabinet idealized for the Wizard (let's add one more dB) that's an increase of 10dB efficiency!!! Which would indeed be twice as loud. So I digress BUT it's true enough that most OEM speakers are a lot better than 95dB and not everyone likes the Wizard.

[soundguruman]

There's really two drawbacks. The cabinet has to be built to specs, weighs a lot, but gives you a lot of loudness.
Also efficient speakers weigh a crap load, and cost a lot.
But if you have ever mic'd a good speaker vs. a junk speaker in the studio, and listen to the playback...
The extra 20 Lbs. almost seems worth it.