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

Do you think the issue is not voltage swing of driver but the current and power it should drive on capacitive load.

@alexberger Generally speaking, yes. Specifically you want to be able to swing the Voltage without distortion. To do that the source that does the swinging must be able to provide the current needed, if any. Power triodes tend to have a bit of grid current anyway even if you aren't driving them positive with respect to the cathode; some of this is due to grid capacitance.

The bottom line is a gutsy driver is needed when driving power triodes of any kind. That is why RC coupling is not the best solution- you use either an interstage transformer or direct-couple; the latter being lower distortion since its a much easier load to drive for the Voltage amplifier (cathode followers tend to have a very high input impedance).

Transformers make distortion of their own even if properly driven and loaded and they limit bandwidth. So if you want the best transparency you don't put them in the circuit. 

The real question in my mind is how many different low powered or SET amps does the average audiophile go through before they find the right amp that matches up well with their speakers to their satisfaction, or before giving up?

3-4 seems typical

4-8 not uncommon

10+ for some

..and then others changing speakers along the way 3-4 times too trying to get "there". The designer of my current amps gave up on SET amps after a few decades and told me he prefers a bit higher power ultralinear amp designs with more versatility anyhow. My journey down the SET path was short lived, but enjoyable along the way fwiw.

@decooney

Great perspective. 

The stock Dynaco 70 measures right up to 35wpc no clipping for 1% THD (good amount of NFB) and almost everyone loves the sweet sound. You do need output tubes that are in really good shape to get the 1% THD (they all need to be tested regardless of brand).

Mods allow lowering of the NFB which gives a bit more dynamic response at the cost of a bit more harshness in the treble with some recordings.

I had Spendor 2/3 speakers for around 5 year. A number of years I used the Plinius 8200 integrated to drive these speakers. But I felt something was wrong and I started looking for a good matched amplifier. I stopped on the McIntosh MC30 vintage monoblocks. It was a great match between amplifier and speakers. MC30 was better than Plinius in everything: more natural tone, better separation, better bass control, more musical. Then I bought an Altec 604E (102dB sensitivity by spec and around 98dB in real). Spendor 2/3 are 88dB sensitivity.

I used Altec with McIntosh first and then tried a 300B SET amplifier. The 300B DIY SET had a big advantage over the push-pull MacIntosh with highly sensitive Altec. Sound was so much more transparent, natural, musical and detailed. McIntosh had more powerful bass but SET bass sounded more natural. My current DIY SET is in a different league compared to my first DIY 300B SET.

One friend of mine moved from his modified Quad II to 300B SET. He builds DIY speakers. But he mostly used the big 15" JBL 4 way clone DIY speakers. These speakers are more difficult to drive than my Altec 604. And he also clearly prefer 300B SET over Quad II.

So, a good SET with matching high sensitive speakers will be a huge step over any vintage push-pull amplifier including Dynaco.