Your journey with lower-watt tube amps -- Can a kit be good enough?

Sorry to be a contrarian, but I did not find the VTA ST70 to be my cup of tea, this even with my own upgrades with resistors,caps internal wire, highest quality tubes. Keep in mind  this at the end of my journey with class a/b tubes. .

Part of the reason I gave up on a/b tubes was inability to get the kind of articulate bass I require. EL34 my fav tube for this class, EL34 mids I love, bass and lack of extension in highs are the downside. This with CJ, Cary, Dynaco, clone, modded Prima Luna. KT family not for me, doesn't have EL34 magic in mids.

So, this in comparison to 845, 2A3, 300B amps  I previously owned or have at present. 845 can drive loudspeakers 300B and lower power SET have no hope of driving, I know I've tried\. 845 successfully drove 90db with benign impedance curve, with 2A3 same speakers sounded like transistor radio. 300B superior to 845 with my extensively modified Klipschorns, while Klipschorns very efficient, 104db they do have an impedance dip to around 2.5ohms at 100hz, this with shallow slope crossover. 845 amps have more self generated noise vs the lower power SET, nearly 1000V plate voltages vs aprox. 400V with the lower power SET. Point is speakers/amp matching important for these SET.

If you have excessively resonant or one note bass with SET you have issues with speaker match and/or output transfomer/ power supply issues with amp. As others have mentioned output transformer quality is critical, power supply is important in that you need something that can supply current with possible lower impedances found in some speakers. I have absolutely no bass issues with my custom build 300B monoblocks or 845 amp with the Klipschorns. And this  with much experience and comparisons  with a/b SS, a/b tubes, class A SS with various speakers.

As to future with SET, at some point I'm thinking Audio Note interstage 300B monoblock kit, Aric Audio 300B or possible 2A3z, Whammerdyne 2A3. Emotive 300B, Triode Lab 2a3 or 300B amps. Again, looking for quality output transformers and power supply.

@sns To be clear, the Klipschorn rolls off sharply below 45 Hz.

The older Klipschorns are not designed to be driven by an amplifier that has a low output impedance like an ST70. You'll know if your speakers are like this (the Klipschorn has been in production since the 1950s which is a bit of a record) if there are level controls on the back for the midrange horn and tweeter.

SETs are a technology which I call the Power Paradigm. PP amps like the ST70 are Voltage Paradigm technology since the ST70 employs enough feedback to allow it to behave as a Voltage source. IOW this has to do with the output impedance of the amplifier; whether or not its low enough for the amplifier to behave as a Voltage source. If your Klipschorns have level controls, essentially they are Power Paradigm technology also and there will be tonal aberrations if you try to use them with an amp that is Voltage Paradigm.

For more on this topic see http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.html

@hilde45 

congratulations. The first thing I would do is upgrade those footers. 

@hilde45 Nice! I'll be interested to hear your comments. I saw that amp on ebay as well and really had to think about buying it just so I could see how far I could push it.

A couple of friends I helped with on their Altec-Onken 102 db horn speaker creations use modified ST35s on rotation when taking their custom modified AudioNote 300B amps out of the loop. They seem to like them and use them quite a bit to save their WE300Bs. I demoed one once, it was different sound from other amps I've tried in my system.  Fairly plush sounding too.