[Steve]

While you're at it tell me how bad my Lowthers suck 

I am sorry Poultry, don't mean any harm.

I am just agreeing with your comment that the sound is flavored.

Hope they never change those Bottlehead flavors.

From the manufacturer's own specs (-3db at 16hz), the amplifier is down at 30hz, some at 50hz, a little at 100hz, even a bit at 200hz, so what can I say, the mids are certainly affected, let alone the lower registers. Add to that, we have not even considered the preamplifier. How do you think world class designers feel about demeaning them with such a comparison? Again, I am sorry, but was just agreeing with you. The OPs question is just how good are the dhts/idhts etc, which I thought meant under world class conditions.

Cheers
Steve

[Rusty Jefferson]

ps. Are you sure the 300b is the most linear tube on the market? Be careful with the claims. 

Of course, I meant the most linear of the tubes (300b/EL34) being dealt with in this thread, though it is one of THE most linear tubes available. It just tends to be transformer coupled amps that reduce it's performance.

There are a couple of huge, gigantic problems with that scenario. First, there is always an output transformer to impedance match to the speaker, unless it is an OTL type, or some other inefficient design. ....

Don't want to get anything started with you Steve as I see you're a regular contributor here, but there is nothing inefficient about Dave Berning's ZOTL output transformerless designs.  You should relax, do some research, and ideally, listen to them. NOT your father's tube amplifiers.

...I am afraid the design presented to you is a compromise for at least two of the output tubes. There is no free lunch....

I would have to respectfully disagree.  Dave's designs are indeed unique.  You may not be a fan of the designs, or knowledgeable, I don't know, but don't make assumptions like this until you've personally experienced it.

 

[Steve]

Of course, I meant the most linear of the tubes (300b/EL34) being dealt with in this thread, though it is one of THE most linear tubes available. It just tends to be transformer coupled amps that reduce it's performance.

Yes, one of the most. It is interesting to check out entire amplifiers as well, say at one/two watts output, as the signal/driver tube becomes more of a factor and also adds distortions, because of the larger signal requirement for the 300b vs other tubes. Any SS parts used for "linearity" purposes present their own problems.

Don't want to get anything started with you Steve as I see you're a regular contributor here, but there is nothing inefficient about Dave Berning's ZOTL output transformerless designs.  You should relax, do some research, and ideally, listen to them. NOT your father's tube amplifiers.

I skimmed and see they are modulating an RF power signal, so yes, the efficiency is pretty good. There are still problems though, such as higher HD and IMD (intermodulation distortion) figures vs typical designs. This will occur even at lower output power levels.

I would have to respectfully disagree.  Dave's designs are indeed unique.  You may not be a fan of the designs, or knowledgeable, I don't know, but don't make assumptions like this until you've personally experienced it.

From Bernings site:

Because the audio signal is riding on a carrier, it is not subject to parasitic elements of the transformer that would otherwise distort the audio signal.

Maybe not as unique as you think. Modulating RF has been around for a long time. Examples include AM (amplitude modulation), FM (frequency modulation), single and double sideband as well. Of course something new, like pulse width modulation etc, has become reality due to precise SS devices .

If the audio tubes are operated in the audio frequencies, class A, AB, and either SET or PP conditions which I referred to, each tube type requires its own particular design in order to optimize the sonic/musical quality. Let's take a look.

From Bernings site:

The 211/845 is a no-feedback design, and uses a large transformation ratio to provide good speaker damping using the triodes themselves to provide the damping through the two-way power transfer inherent in the ZOTL.

I see they are modulating high voltage/low current RF with the audio signal, then changing audio modulated RF to low voltage/high current through the RF transformer at 250khz. The final basic step is eliminating the RF, with only the audio/musical signal remaining.   

When modulating RF, we can drive the grid, plate, frequency modulate the "carrier", pulse width, single/double sideband, or some variation etc. Let's check out some typical modulation techniques.

With respect to AM (amplitude modulation) via a grid(s), each tube type requires an optimum design for optimum musical quality and low distortion. One design does not work for all.

With respect to AM plate modulation, high audio power is necessary to drive/modulate the RF. Each type/tube number output tube definitely requires an optimum design. An optimum design for 300b will not be optimum for an EL34 or 6L6 type.

Let's say FM (frequency modulation). In that case a typical audio signal (not high power) alters the frequency of the RF carrier at the audio/musical rate. That drives the 300b/EL34/6L6s, being the RF tubes.

Notice in the manufacture's own words, the tubes affect the sound, thus the need to optimize the design to each tube type, 300b/EL34/6L6.

There is one more problem on the webpage, that of otl amps "are starved for current". That can be said for any tube amplifier when high distortion or clipping occurs. However, we have the speaker driver DC coil resistance, Xover inductors in series with capacitors etc to limit maximum current from the amplifier. By the way, my old personally designed triode OTL amplifier produced 160 watts rms into 8 ohms at 0.4% total harmonic distortion, so where is the current starvation? It is true that an OTL does require a lot of AC power and does produce a lot of heat compared to typical amps.

Cheers
Steve

ps. By the way, one can design near perfect amplifiers using output transformers.