Amps Atma-Sphere M-60 Mono blocks OTL design

^^ Rear right and rear left are the input tubes, in parallel.

They are part of a single gain stage called a differential cascode, common in solid state circuits but unusual in tubes- when we first started using this topology we were the first to do that in a tube amplifier.

The middle tube is the top of said cascode circuit.

Therefore the two bottom tubes in the cascode circuit are the most important in the amp for sonics, followed by the top tube in the cascode (rear middle position). 

The front tube has no gain and is the driver for the output tubes. It controls the Bias and DC Offset. It should be a -GTA or -GTB if using NOS types.

I believe a more compelling and "competitive"  comparison would be the Line Magnetic 805ia.  This is a very highly praised 805 tube SET with 45 watt output.  Of course with these types of comparisons, final choice has much to do with plain old taste. Both of these fine  amplifiers will have their passionate and loyal advocates.

The speakers used are going to play an enormous role in the results! In this case, the Line Magnetic is at a bit of a disadvantage due to power, not just because its only 45 watts. The problem is that if you really want to know what the two amps can really do, the LM should not be run past about 20% of full power for its best results (otherwise the higher ordered harmonics tend to show up in its output). That's about 10 watts. Ozzy's speakers seem to be about 90 db or so; that really isn't going to allow the LM to strut its stuff without a lot of distortion unless you keep the volume down.

We have a lot of feedback from our customers on this sort of comparison.

These things never move in only one direction.

When I first got started decades ago it took me a while to get used to the fact that people would sell our amps and look for something else.

Over the years though the one thing that has really shown itself over and over again is how successful the initial setup of the amplifier installation actually was. If that was right (meaning: the right speaker load, short speaker cables, a competent preamp and front end to drive it) we found that owners tended to hang on to their gear. I don't know if owning it for decades until death counts, but if it does then the above quote is false.

This is why we developed our update and warranty reactivation policy, so owners of older gear could keep it current.