[sdiy] Tube amplifier question

[jhaible at debitel.net]

I've aquired a taste for building tubes stuff right now. (;->)

I want to build a small amp that will replace the Studio monitor amp
and the HiFi amp in the basement. Right now I run both thru a cheap
Sony HiFi amp.

I think of something like this:

Small power amps with 2x EL84 push pull for the speakers (I never hear
music very loud over speakers, so that should be plenty)

Separate Headphone amp with EF86 (connected as triode) and 12BH7 as
cathode follower with no overall negative feedback loop.

Phono preamp (yes, for my old records) with 12AX7 and passive equalisation

This all should fit into a 19" enclosure, 2 or 3U high. No need to display the 
tubes outside (;->)


Now I have the following questions:

(1) Is the 2x EL84 pp a good choice for a "transparent" HiFi amplifier?
    Is there an alternative that is only slightly more expensive (no vintage
    tubes in the 100 dollar price range), but which would give much
    improovement?

(2) Is an ultralinear transformer the way to go? I have seen some "famous"
    amps like the Quad II use cathode feedback instead of the ultralinear
    configuration (other tubes, too, of course ...). What's the general
    pro and con of ultralinear vs. cathode feedback, or should I even use
    both ? (I see that the winding is easier in ultralinear, and these
    transformers are very common, so I'd need a good reason to do it
    otherwise.)

(3) Is the headphones amp with EF86 and 12BH7 a good idea? Should I use
    an output transformer, or bring the output impedance down with a WCF
    and don't use a transformer? (My Sennheiser HD450 phones are 300 Ohm
    types, and I can get down to ca. 100 ... 150 Ohm with the 12BH7 in
    WCF configuration. Not much damping then, and I worry about the transients
    thru th ephones during power-on.

Any ideas, hints, recommendations?

Thanks in advance,

JH.  



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