Living With A Class A Tube Amp

Amplifiers employing tubes often present a larger, deeper sound stage that some term ‘halographic.’ Tubes also have a distinctive distortion signature that I notice most with guitar treble. Jimi Hendrix and Stevie Ray Vaughan solos sound like they’re playing different instruments when reproduced with transistor vs. tube amps. The transistors result in clearer, cleaner sounds; but the tubes sound like what I remember from the 70’s (in Jimi’s case). That reverberating, echoey sound can’t be reproduced by transistors, in my experience. 

There was a time when this was true but no longer. I'm not saying that all solid state amps can do all the things that tubes can, but there are some out there and notably, are not as expensive as tube amps of the same power. For me this is about good low level detail retrieval, with an involving sound that is smooth without harshness or brightness. Tubes used to rule the roost on this but that has changed.
 

@immatthewj FWIW, 'pure class A' is a marketing phrase. As far as engineering goes, a circuit is either class A or its not. None of this 'enriched class A' stuff you often see (such amps are class AB). In your case my guess is class A1.

@immatthewj Class A, if we are talking about tubes, comes in three flavors, A1, A2 and A3 (recently patented).

If the amp really does get hotter when you push it and it really is class A, then its class A2. In class A2, grid current can exist during part of the audio waveform so the driver has to be a bit more robust in order to maintain linearity during that portion of the cycle. Our OTLs are class A2.

Sometime in early '20 I replaced them with a set of the reissued Russiian Tung Sols and they have held up beautifully (however, I don't run them as hard and no mishaps involved).  

@immatthewj If the amp really is class A, you do run them as hard. How loud you play the system has no bearing on the heat or tube life.

If the amp is class A1, if you were to put an Ammeter in series with the AC line, you'd find the current draw unchanged regardless if the amp is at idle or full power.

This is not a class A amp. It is a push pull.

@carlsbad2 Push pull amps can be class A no worries. The Dynaco SCA35 using a pair of EL84s was a class A PP integrated amp. We’ve been making class A triode PP OTLs for decades.

If you were not aware that amps other than SETs can be class A, now you are. The trick is just the same as in an SET- the power tubes do not go into cutoff during any portion of the output waveform right up to full power. So you can also have class A solid state PP amps too.

@jrcotner Tube amps running class A have hotter running power tubes and that always means shorter tube life on account of the heat. To get the most out of the tubes they should be kept free of dust and fingerprints, have adequate ventilation and the speaker load should be benign (they will run hotter if the speaker is 4 Ohms on the 8 Ohm tap for example, because more of the power they make will be dissipated in the tubes themselves rather than in the load).

There are amps of other classes of operation now that have all the good properties of the best of class A; this is true of even some class D amps now.

The reason for class A is to maximize linearity out of the output section; the less work the feedback (if any) has to do to correct the output the better. In the old days I think one concern was crossover distortion but I’ve yet to see a PP amp that actually had a problem with this as long as it was biased correctly.

In case you’re not aware of it, the differences you hear between amps is mostly the different ways those amp make distortion. IOW the distortion signature of the amp is also its ’sonic signature’. Once you know this, then its easy to see that the distortion signature is actually what is important and not the class of operation.