[sdiy] Tube amplifier question

[Thomas Holley]

I think EL84 are a fine choice. They will give plenty of power for a home
unit. Another output tube that you could consider is 2A3 direct heated
triode. They are quite good and can be found fairly inexpensively. They are
quite a bit bigger though and may take a 5U rack space to contain them.

Your headphone amp sounds OK to me. One place that has lots of different
headphone info is headwize http://www.headwize.com/.

Good luck,
Thomas
----- Original Message ----- 
From: <jhaible at debitel.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, August 04, 2004 5:26 AM
Subject: [sdiy] Tube amplifier question


> 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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