Is a Tube Amp Capable of High Current?


I need your help.

I have a pair of VERY inefficient speakers (Platinum Solos), but am also a big fan of tubes. I know that tubes can work with power-hungry speakers as I have done it with a pair of Magnepans...BUT...I'm not certain that it will work in this case.

The speakers are rated at 84db with a nominal impedence of 6 ohms.

I am purchasing an Audio Research D-125 which is rated at 115wpc.

I know that people always say that "tube watts" are more powerful than solid state watts, but I'm not really sure what that means. I also always hear people say that you need a "high current" amp. I've always taken this to refer to solid state, but can this be true of tube amps as well? Is the ARC D-125 high current?

I'm not a head-banger and certainly prefer quality over quantity when it comes to sound. Also, my room is not particularly huge, so that shouldn't be too big of a factor.

I need your advice. Am I setting myself up for disappointment? Does a load like this inherently require solid state amplification?

Thanks!
dan53e1
There are a number of tube amps that will be able to handle that sensitivity. I can't comment on specific matches, but I can tell you that there are several (VTL and smaller) that might work. Feel free to email me if you want any specifics on my own experiences with other speakers. I have been on a real quest to match my current and planned inefficient speakers with "tube-like" SS. I can tell you that it will be much easier and cheaper to find high current tube amps than tube-like SS...

BTW nice answer Ghostrider!

Best of luck,
Jacob
We represent the Wyetech Labs SET Tube amps and found them to drive very difficult speaker loads better than much higher powered tube amps. the Topaz stereo amp which is rated at 25 watts can out drive my 175 watt Airtight monos. a very well designed power supply is the key!
I agree with artistic audio...power supply takes the cake. I've heard any number of well made lower powered tube amps, drive the hell out of something that the numbers indicate would be a mis-match. Consider the size of your room-the type of dynamics that are important to you and audition. Wright sound company makes amps that drive things they shouldn't....I've heard their 2a3's drive and 86db 8 ohm speaker at 3.5 watts, its not a combo I would advocate but the fact that it makes good music makes a point...their 300b amp drove the speakers as loud as I could stand-check them out at www.thewright-sound.com

good luck,

cbird
Thanks Everyone!

It seems then, if I'm understanding all of this correctly, that high current is what's needed to push the power into highly resistive or low impedence loads? So if my speakers stay somewhere close to 6ohms w/o much in the way of wicked impedence curves, I should be fine with just some high wattage, correct?

The ARC amp that I'm in the process of buying weighs close to 100lbs so I'm presuming that it has the kind of HUGE output transformers that will be required.

Here's another question...If my speakers are 6 ohms, should I use the 4 ohm or 8 ohm taps? Should I be conservative and go with 4?

Thanks again for all of the insightful advice. I think I'm starting to get it.
The idea of a 'high current' amplifier is a bit mythological. If your speaker is a 6 ohm load (not particularly difficult for tubes, BTW), then it is easy to show, using Ohm's law, what is really happening.

Let's say that you've settled on a tube amp that produces 115 watts. Let's further say that you have a transistor amp that will produce the same power into 6 ohms. By using a little algebra (Ohm's law is Resistance = voltage/current), we can derive how much current will be flowing in each case.

Power = (current)squared X Resistance, so:

115 = (4.38) squared X 6.

This is the same regardless of whether it is tube or transistor. IOW, 'high current' has little or nothing to do with it.

You'll probably want to use the 4 ohm tap to keep the load on the output tubes at a good operating point for low distortion.

Since the amp specs are rated from its 8 ohm tap, it likely that you will have a little less power on the four ohm tap as the transformer is less efficient on the four ohm tap. The loss will be minor.

My guess is the real issue is whether or not 110-115 watts is enough power. Unless you are in a really small room (and depending on your listening habits) there's a good chance you'll be running the amp out of power if you try to play it loud.