Tubes/SS Power Amps?

Orpheus10, there are inexpensive ways of dealing with heat. You don't need air conditioning for starters, if you do it right.

Now if you set up your system according to how much heat it makes, don't expect it to sound like music. If it does, great, a happy coincidence.

Hot transistor amps are hot because they employ a greater amount of A operation in their output- this is to improve linearity. The same is true of tubes, but they are inherently more linear in many cases.

One thing is certain- all the solid state embodiments known so far make more odd ordered harmonic distortion than their tube counterparts. Odd ordered harmonics in trace amounts are easily detected by the human ear, which recognizes them as brightness and harshness.

So you might look into the idea of creating ventilation in your room to get rid of heat without air conditioning. I have seen this done quite successfully, such that you could sit in the same room with 2 class A 500 watt triode monoblocks all day and all night without getting uncomfortable, and without air conditioning.

Orpheus10, amps in general are not supposed to catch fire :), tube or solid state.

Sounds like that SS amp was overbiased and went into thermal runaway.

The way to do the ventilation is to put one are two vents over the space that the amp/amps will occupy. You can get flexible ductwork inexpensively that can then be routed to the outdoors by a small squirrel cage fan. If you do it right, it will be quite unobtrusive. If you live in a northern climate, you may have to take some simple steps to prevent the ducts from being a heat loss in the winter.

This approach is cheaper, quieter and more reliable than air conditioning.

We've been looking at class D for 9 years now. We have certainly thought about it.

The preamps we make now would work fine with any Class D amp.

The concerns we have had are: is class D a threat to our tube technology? Answer, yes, although not with any current embodiments. However Class D is the rising star in amplifier technology and if its still early on the price/performance curves it may yield something yet.

Second, should we be building one? Answer, maybe. It could well be poor marketing on our part to not have a class D amp in our lineup, as we have been focused on getting as close to sounding like real music as possible. So far that has been easier with tubes, but I am pragmatic enough to know that that could change!

Orpheus10, just FWIW if you think we can't see the frame rate at a movie theatre, go see the Hobbit and then go see the HFR (High Frame Rate) version of it!

One thing that Class A tubes have over Class D is bandwidth. How about full power -1/2db at 150KHz, only 2 db down at 300KHz? Some might argue that class D (and for that matter, traditional transistor technology) have more current (and they would be right) but the question is 'Is that important?'

The correct answer is no. High current ability is not particularly important. Why? First, look at the specs of any transistor amp, any class D amp, in particular the distortion spec into 4 ohms. You will see that the distortion is higher into 4 ohms than it is into 8 or 16 (likely the 16 ohm distortion will not be spec'ced, but it is lower...).

To put this more clearly, if you want to have the system to sound smoother and more detailed, even if you have solid state, that will be easier if you are driving a higher impedance. This is because that increased distortion (driving lower impedances) will mask detail and come off as brightness. This is the difference between a good hifi and a music system that sounds like real music- the lack of electronic artifact.

Now, on top of that, about 50 years ago tubes were being declared obsolete, much like vinyl LPs were in the 1980s. The fact that tubes are still very much a part of the audio marketplace is not some sort of fluke- they are still here because they are still popular half a century on. This is the more telling fact actually. If tubes were really obsolete they would have been gone decades ago. In fact these days its easier to find old tubes than it is to find old obsolete semiconductors...

Generally speaking class D amplifier modules are less expensive. I have a 100 watt/channel module that cost $25 each in low quantities. It is the size of a pack of cigarettes, including heatsink, input/output connections and power supply connections. All you add is the power supply and the box.

Yet what I see in the marketplace are amps that cost nearly as much as their traditional SS brethren. Its pretty apparent to me that the main push for class D is that you can make a lot more money selling them.

I've been looking at methods of incorporating more tubes into the process. There is even a method of using a power tube for output switching.... the problem with using them though is you can see through your hands when the amp is on.

It was a joke. If you run a real high voltage on tubes they can emit X-rays.