What is needed to build a tube amp and what non?


What it should it not contain the tube amp? IMO, NFB that press the scene of the sound sending the part of signal back into the previouse stage. Unique amp must be built lineary without NFB, /in some causes linearity doesnt mean best sound/. IMO, never use tone control that change the sound. If You need more bass, use big bass speaker, if You need more high freeq. - use sensitivity tweeters, if You need meedle fr. - use sensitivity fullrange not less 8 inch. IMO, Hi End is back proportional to the number of composite parts - use simple decisions with not cheep parts- cheep parts - cheep sound!. Every passive part change the sound. IMO, in SE iron for OT must be 10-20 time more than output power, /for 5 W never use 5 W OT, but 50-100W/. IMO, in power supply use kenotrones, that provide soft start and soft amazing sound. Every time use iron chock and hmmm will be far from Your ears. IMO, do not use iron enclosure that collect noises....But your opinions?
azazello

but one bad side for OTL, OTL is close to PP.
That is certainly open to debate. It all depends on execution. Without an output transformer, its much easer to build an amplifier that has no crossover issues whatsoever.


Azazello,
It was not made clear in my post but I have been a SET  owner for 9 years.  You state that you're more "extreme" than I am. I suppose you have a point given that I just believe every topology has strengths and weaknesses. There are compromises if one chooses SET and I accept this reality. The positive attributes far outweigh these compromises in the overall scheme of things.  The dominant attraction for me is the purity of tone and virtual absence of the pervasive electronic or Hifi sonic characteristic I hear with other alternatives. This sheer naturalness is a necessity for me now that I've been exposed to it. This elevates the level of realism significantly. 
Charles 
--atmaspfere....With OT quality of sound of amp depends to OT, construction, kind of wire, kind of iron, wiring....But propertys, peculiariy of sound of every tube penetrates cross OT and SE /I feel/ sounds more warm and I can listen more hours. But OTL is better in some situations, sounds without breaks between tubes and speakers /without cap in output - OCL/, the sound is very deep, clear, bass in my OTL starts from 5 Hz!! But must have fast fuse if both sholders are disbalansed /if some sholders is out of mode....speakers are connected to common resistor with output currents in oposite directions for resulted 0 A/. But OTL has phase invertor like PP and signal goes between sholders and sound is close to PP.But I like my SE 2A3 RCA and my OTL 6AS7GE....
Charles....I accept Your words and Im allmost agree....Different tubes in SE sound different cool, I prefer my 1 W  SE EL11 Telefunken in triod, that sounds better 300B....Every time I compair 2A3 RCA and EL11 Telefunken.
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But OTL has phase invertor like PP and signal goes between sholders and sound is close to PP.But I like my SE 2A3 RCA and my OTL 6AS7GE....
Not all OTLs are built with a phase inverter. Ours aren't- the output of the voltage amplifier goes directly to the driver tube, without an intervening phase splitter. The driver tube is then direct-coupled to the power tubes, which are in turn direct coupled to the loudspeaker. A fuse for the B+ of the power tubes has been shown to provide plenty of speaker protection over the decades...