# dual 6V6 amp output question



## Lincoln (Jun 2, 2008)

Is there a simple, easily understandable answer to why some amps with two 6V6 tubes produce 18 watts (Fender tweed deluxe) while other amps using two 6V6's are rated at 30 watts? (Garnet Lil'Rock/Rebel)

Higher power tube voltage?
More gain in the pre-amp stage?

I'm confused


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## keeperofthegood (Apr 30, 2008)

Lincoln said:


> Is there a simple, easily understandable answer to why some amps with two 6V6 tubes produce 18 watts (Fender tweed deluxe) while other amps using two 6V6's are rated at 30 watts? (Garnet Lil'Rock/Rebel)
> 
> Higher power tube voltage?
> More gain in the pre-amp stage?
> ...


http://www.schematicheaven.com/bargainbin/garnet_b90l_l90l_lilrock.pdf

http://www.schematicheaven.com/fenderamps/deluxe_6g3_schem.pdf


I "think" the difference is 70 volts.

The Garnet Lil'rock has 435 volts on the 6L6 plates and the Fender Delux has 365 volts.

http://www.nj7p.org/Tube4.php?tube=6L6

That would suggest that the Garnet is over-driving the tubes some. The highest plate voltage in the list being 400 volts in the class *Push Pull Class AB2 Amplifier (Fixed bias)* configuration.


I wonder what the deal is too kqoct


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## Blueskidd96 (Aug 26, 2009)

Also remember that the output transformer is a large part of the equation.


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## keeperofthegood (Apr 30, 2008)

Blueskidd96 said:


> Also remember that the output transformer is a large part of the equation.


There is that too yes. Sadly, transformers are one of the poorest labeled parts in ... anything really. Even when labeled often the company either doesn't keep information on them or never had it to begin with >.<


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## Ripper (Jul 1, 2006)

Alot of it comes from the voltage on the tubes, Gar ran the lil rock tubes with more voltage than what your typical fenders are and if you get right into it, fender ran some of their over what the manuals recommended as well. The old tubes could easily take it. The other thing to remember is also that the voltage isn't nearly as important as the plate dissipation. If the tubes pull too much current things go south, they are far more tolerant about voltage. Old tube manuals will tell you that a pair of 6V6's can draw 92-94mA on the plates for the pair but you won't find any amps running a pair anywhere near that.

They tried to run more voltage to get cleaner output and louder. Strangely it didn't work in the Lil Rock. A fantastic amp but it ain't known for it's clean. My lil rock runs a plate voltage of around 452 volts and I've never had a problem with tubes in it or any problems with it working. Just keep the bias set properly and it's all good. Alot of those voltages you see on the old schematics are from when the line voltage in a house was 110 not a 120 or 125 volts.


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## Ripper (Jul 1, 2006)

For what it's worth the output tranny on a Lil Rock is pretty much identical in specs to the ones on a fender deluxe.


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## nonreverb (Sep 19, 2006)

The output tranny primary impedance is a factor in determining wattage as well...


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## Wild Bill (May 3, 2006)

nonreverb said:


> The output tranny primary impedance is a factor in determining wattage as well...



A lot of the confusion also comes from how the amp company measured the output power!

There's no set standard, at least not one that someone in advertising and not engineering couldn't bend!

The data sheet specs are concerned with hifi conditions. You set the amp up into a dummy load, put a 'scope on the output and then advance the gain on the input until you just start to see some distortion and then back off a bit to keep things clean. You measure the output voltage swing, add in the value of the dummy load and then it's just a simple formula to calculate the output wattage.

This is a very easy test to "fudge"! First off, you can't see much less than 3-4% distortion on a 'scope trace anyway! Also, we're talking guitar amps here. A certain amount of distortion is a given, if not actually desired. How much? That depends. How much power do you want to claim the amp puts out?:smile:

Pete Traynor never had much respect for how his competition measured output wattage. He knew it was mostly crapola. That's why he preferred not to bother. Much of it is also amp voicing. To the human ear, a bright amp will always sound louder than a more mellow one, even at the same power level.

To make things even less important, the human ear needs a 4x power increase to make a noticeable increase in volume. That means from 5 watts you need to jump to 20 watts. The difference from 20 watts to 30 watts is just not that big a deal to our hears, at least not by itself. If we're talking a very bright AC30 it will matter more, not because of the sheer wattage as the treble boost.

Plate voltage by itself doesn't mean you can safely get more watts. Higher plate voltages means you have to bias for less current to keep from burning out the tubes. The dissipation ratio stays the same. Watts is Voltage x Current, after all. Still, if you're going to abuse a tube by going beyond its specs it seems they handle higher voltages better than excessive current. With higher currents redplating shows up very quickly but with higher voltages you can keep the same or lower currents. You're still hurting the tubes but it shows up as decreased tube life. Instead of over 10 years in hifi service you might get less than 2 years in a guitar amp. Most musicians think that to be a good trade-off!

:food-smiley-004:


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## John Bartley (Jul 23, 2009)

Amp power rating is one of the things that has always made me wonder with amusement. Under lab conditions, where the performance of a tube is properly (scientifically) traced, there's a certain set of standards applied. The "usual" rating applied to a 6V6 variant tube is somewhere between 10 and 14 watts in push-pull configuration, depending on voltage and current control levels and amp design. However, all tube amps, particularly guitar amps, will have voltage spikes, and it seems to me that some advertised ratings are given based on the spike voltages of a manipulated test tone, rather than the smooth, "clean frequency" test voltages of a lab supply. An unethical advertiser could certainly claim 30+ (or whatever) "peak watts" if they were measuring the spikes. It would be like claiming that a car motor can deliver 500hp instead of 250hp. It certainly might.....for about 15 seconds, and at 10,000rpm, just before it spits a rod out thru' the crankcase....

just a thought....

cheers

John


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## Lincoln (Jun 2, 2008)

Thanks guys, great answers! :bow: 
Sounds like it's more about marketing than it is about magic. 




John Bartley said:


> An unethical advertiser could certainly claim 30+ (or whatever) "peak watts" if they were measuring the spikes.
> 
> John


Reminds me of an amp that's on Ebay right now. 250 Watts, 6" speaker, and it only weighs 9 pounds!!!:banana:


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## parkhead (Aug 14, 2009)

Lincoln said:


> Thanks guys, great answers! :bow:
> Sounds like it's more about marketing than it is about magic.
> 
> 
> ...



we have a winner 

RMS ?

Peak Power ? 

Burst Power ? 

its all Horse Doo Doo Marketing 

P


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## nonreverb (Sep 19, 2006)

Lincoln said:


> Thanks guys, great answers! :bow:
> Sounds like it's more about marketing than it is about magic.
> 
> 
> ...


Yeah 250 watts...it's too bad some people don't know what they're talking about. In many cases, they are quoting the input power requirements they see on the back near the mains input. Which, of course will be substantially higher than the output wattage....


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## mhammer (Nov 30, 2007)

My favourites are the $10 plastic computer speakers with 3" drivers that can produce 360W "PMP", apparently on 6 C-cells.

Yep, there are lies, damned lies, and audio power ratings.


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