Question:
Hey all you technical peoples(you know who you are) I've got this idea and I was wondering what you guys thought.
I have a 120w tube amp w/ 4 6L6's and, as you can imagine, it's hard to get power tube saturation with out going deaf. To help with this problem I was thinking about pulling 2 of the power tubes and plugging the speakers into the 16ohm jacks(normaly plugged into the 8ohm), and then if I still can't get power tube distortion at gig volumes I'll get an attuenator.
Just so you guys know, this amp is not for practicing at home and is used soley for medium sized gigs(300-600) people. Also, I am fully aware that 30w of tube power is all the powere I would ever need...but I already have this amp, and it gives me the tone I want.
Answer:
Yeah, that's a common practice, although you have the impedance backwards, I think. When you pull a pair of power tubes (either the inside or the outside pair) you want to select the impedance on the amp to 1/2 of what the speaker load actually is, not the other way around.
You might be surprised at how little difference it makes in the overall volume though - its only a 3 db drop, which ain't much, but it is going in the right direction. That's why I recommend to someone buying one to go no higher than a 50 watt amp (unless you're literally going to use it for arena-sized gigs); the volume is only slightly lower - almost negligible, re-tubing is cheaper, it weighs significantly less, costs less to buy, and usually will sound a little better than its 100 watt counterpart since the power tubes are getting worked a bit harder for the same volume.
Answer:
Originally Posted by Major Tom Yeah, that's a common practice, although you have the impedance backwards, I think. When you pull a pair of power tubes (either the inside or the outside pair) you want to select the impedance on the amp to 1/2 of what the speaker load actually is, not the other way around.
You might be surprised at how little difference it makes in the overall volume though - its only a 3 db drop, which ain't much, but it is going in the right direction. That's why I recommend to someone buying one to go no higher than a 50 watt amp (unless you're literally going to use it for arena-sized gigs); the volume is only slightly lower - almost negligible, re-tubing is cheaper, it weighs significantly less, costs less to buy, and usually will sound a little better than its 100 watt counterpart since the power tubes are getting worked a bit harder for the same volume.
Thanks tom. So are you saying that my theory would work, and i could achieve power tube distortion at lower volume levels...or are you saying that it won't make a difference as far as saturation is concerned?
You're right about lower wattage tube amps...oh well, we live and learn...but you need to here this monster when the power tubes start to break up
Answer:
i was under the impression that pulling a power tube pair reduces the power by half...thus taking it from 120 to 60w (still beastly loud)...is that really only a 3db difference?
Answer:
Originally Posted by thesteve i was under the impression that pulling a power tube pair reduces the power by half...thus taking it from 120 to 60w (still beastly loud)...is that really only a 3db difference?
Pulling a power tube doesn't reduce the output by 1/2(or in my case 1/4) it just makes the remaining power tube(s) work that much harder....or at least that's what I'm hoping.
Answer:
Originally Posted by thesteve i was under the impression that pulling a power tube pair reduces the power by half...thus taking it from 120 to 60w (still beastly loud)...is that really only a 3db difference?
Check it out. Read the first myth. As strange as it might sound, it is true.
Answer:
Originally Posted by BlessedNinja Pulling a power tube doesn't reduce the output by 1/2(or in my case 1/4) it just makes the remaining power tube(s) work that much harder....or at least that's what I'm hoping.
well here's the thing...in alot of amps (i would think it safe to assume yours is this way, being a peavey) operate their power tube sections in a "push/pull" config. this basically means if you pull a single tube you'll royally screw up your amp...you have to pull two, and they have to be one "push" and one "pull" tube...or you're screwed.
that being said, in your scenario the idea of output reduction and "making the remaining tubes work harder" will accomplish practically the same goals. as far as the output changes, only tom can answer that, but i think it's what was was alluding to with the "3db loss" concept.
edit: i know that it takes ten times as many watts to double your perceived volume...i just couldnt' remember if 3db was the difference achieved by doubling wattage.
Answer:
I've done it with a Twin and a Bassman 100 (the only four power tube amps I've had a chance to really mess with)...Tom's right, the difference in volume is negligible, but I did hear a difference in tone.
Answer:
Originally Posted by PianoMan Check it out. Read the first myth. As strange as it might sound, it is true. That was a good read.
Answer:
Originally Posted by Mattlock That was a good read.

Answer:
Thanks tom. So are you saying that my theory would work, and i could achieve power tube distortion at lower volume levels...or are you saying that it won't make a difference as far as saturation is concerned?
You're right about lower wattage tube amps...oh well, we live and learn...but you need to here this monster when the power tubes start to break up
What you are doing is essentially converting that 120 watt amp to a 60 watt amp. The 2 remaining tubes won't be working harder at the same level, but since there's only two, the amp power will be cut in half, resulting in a volume drop of 3 db.
The way sound and our perception of it works is not a linear scale, its logarithmic or whatever - doubling the power of an amp only results in a slight increase in sound pressure level, which is 3 db. Humans perceive "twice as loud" as being an increase of between 6 and 10 db. Say if you had a 50 watt amp and you wanted it to be "twice as loud", the very minimum you would need is a 200 watt amp, which would be the 50 doubled for +3db and then doubled again for another +3db. Some say 10 db is roughly twice as loud - in that case, double that 200 watts again for another +3db = 400 watts. Going from a 50 to a 400 watt amp is an increase of 9 db (pretty close to 10) - that should get you twice as loud.
Of course, it works backwards too. Say if you wanted that 120 watt amp to be half as loud. Halve the power to 60 watts = -3 db, halve again to 30 watts = another -3db, halve that again and the result is 15 watts for a 9db reduction. So "half as loud" would be between 15 (or less) and 30 watts. That explains why 15 and 30 watt amps can get so loud - they are only a couple notches down from a 120 watter...
Oh yeah, speaker efficiency - the amount of volume put out per watt of amp power by different model speakers varies a bunch. I think most 12" guitar speakers efficiency ratings fall between 94 and 101 db at 1 watt/1 meter. That's a difference of 7db, but lets say 6 for easy math. Now take the 120 watt amp with 4 speakers rated at 94 db @ 1 watt, and compare it with a 30 watt amp with 4 speakers rated at 100 db @1 watt. All else being equal, those two amps should be producing the exact same amount of acoustic output. As one example, I have a 15 watt tube amp in a 2x12 with speakers rated around 100 db/1 watt. That thing is LOUD! , enough to keep up with a pretty loud drummer.
Answer:
Thanks everyone, I think that's what I'm going to do.
My next question(this ones realy stupid...but you can never be to careful) would be wether or not I could use a 60w attuenator w/ this setup?
Answer:
hmm...that's actually a really good question...something i've never thought about.
i would go out on a limb and say yes, since the wattage is reduced from 120w to 60w, the attenuator requirements would also change.
Answer:
Originally Posted by BlessedNinja Thanks everyone, I think that's what I'm going to do.
My next question(this ones realy stupid...but you can never be to careful) would be wether or not I could use a 60w attuenator w/ this setup?
Sure.