How much power...

[JoeCon]

Gentlemen,

Some local guitar players came by to try my amps. I built a 2 x EL84 Rocket and a KT66 Rockster. The question always comes up..."how much power these got?" I never know what to say to that.

The Rocket has a 20 watt OT and the Rockster a 30 watt is this what I should tell them? Even though the Rocket is running 14 watt per tube and the Rockster 24 watt?

How to answer that and be realistic about that output power? What do you other builders say when the power question comes up?

Thanks....

[Leo_Gnardo]

14 watts per tube what - plate dissipation or delivering power to a load? It's the second that counts to consumers.

I measure amps driving load resistors, run 'em up to the clip point then back off a tiny bit, measure the AC voltage & use V^2/R to calculate power at clip. Most guitar manufacturers measure at 5 or 10 or 20% distortion because "those guitarists love distortion." I've found you can add @ 12% power for every 5% increase in distortion. So a 10W amp clean becomes a 15W amp in deep clipping. A 100W amp becomes 150W.

MI manufacturers often don't publish the distortion figure at which they derive their power figure. OTOH Hi Fi manufacturers love to quote some tiny distortion figure say 0.001%. Funny thing, one of the most respected hi fi manufacturer, McIntosh, quoted distortion figures of 0.5% at power for their highly reliable and collectible tube power amps in the 50's and 60's. And nobody ever complains much about distortion from their Macs.

[JoeCon]

Leo

Sir, so I need load resistors, freq generator and scope to do it right?
Funny how the "power" is so important. Rather than listen to the amp and decide if you like the sound of it...

Thanks...

[TUBEDUDE]

I try to discuss SPL, speaker efficiency and cabinet design also, as these elements of the equation are often missing in many players understanding of electrical power to acoustic power.

[Leo_Gnardo]

I need load resistors, freq generator and scope to do it right?

Yes that's what it takes & o'course cables clips & like that.

Funny how the "power" is so important. Rather than listen to the amp and decide if you like the sound of it...

Well some people need a number to hang their hat on.

There's a couple other things besides. Depending on what size venue your customer might be playing, does their band have a monitor system, what kind of tone they're looking for. If they have monitors, a guitarist can get by with a small amp if its signal can go to monitor mix. If not it's going to take extra power to cover the stage - and maybe the audience. If you need loud clean tones for any part of the program there is no substitute for power, and efficient speakers help there too. Funny thing about the ear - it interprets distortion as "power" so if the band is always playing music that demands distorted guitar, again you can get away with a fairly low power amp.

[Bob S]

It's a moot point to us.
I had one guy tell me a Rocket is way too loud.
4 x el84's running around 30-32w.
So I loaned him an Express biased @ around 36w.
Kinda put thing in perspective.
He was comparing them to a solid state amp spec'd @ 30w...
I stick with sound pressure & punch.

[Stevem]

If you go and look at the tube spec sheets you can get a feel for how much power your build(s) output, in fact I can not belive that you have built more than one amp from the get go without consulting these charts!
A difference of 15% in wattage from these charts/specs will hardly be heard in terms of volume, it will make for earlyer output stage clipping to be heard.

[JoeCon]

Bob

And after you have built and played a few amps and you see a dual EL84 amp vs. a dual El34 you know what to expect. All I was able to say honestly was the Rocket was a little less power than the Rockster. But not a "Fifty Watt" amp was the main problem. But the Rockster opened up even through a single 12 got some attention...

Guitarists are weird! LOL.......

[Cantplay]

Its the same with home amps.

Try to sell the mainstream consumer a ¾ watt amp.

Most will not believe it can go 'too loud' until they hear it through the right speakers.

Horespower sells cars even though torque is what accelerates them.

John

[overtone]

You could say "adequate" with a smile of confidence, just like Rolls Royce always answered such questions.

[Bob S]

Yeah - there's very little perceived volume difference between 30 & 50 W.
Speaker efficiency & the response of the amp design are factors.
I think of the Rocket design as being (quite) polite.
The Express is a beast.
And output tube spec sheets are part of equation...

[Leo_Gnardo]

Guitarists are weird! LOL.......

You noticed?

@ 30 years ago I modified a vibro Champ & got @ 19W clip out of a pair of 6V6. Speaker was a stock Peavey Scorpion. At the time the only place in the neighborhood I could check it out was a small engine repair shop - lawnmowers, snowblowers, chainsaws, they're used to noise. The owner kicked me out because tha amp was too loud & he couldn't stand it. Imagine that...

[JoeCon]

Leo

I'm one so I have noticed!!

Been thru the 100 watt Marshall phase and now love my 20 watt Rocket. It's tone not volume that rocks. And "power" is pretty meaningless considering all the possibilities of pickups, tubes, and speakers that can go into the equation.

I guess these young guys just need a little education...

[pdf64]

Knowing the power output of an amp, both at the point of clipping and heavily overdriven, is important info when selecting a suitable speaker/s.
Pete