Sander deWaal wrote:
"Andre Jute" said:
These, incidentally, are the same test results I interpret as meaning
that there is no such thing as an SE sound, that what we hear which so
appeals is a Class A ZNFB or very low NFB sonic signature. People just
confuse Class A with SE because only a tiny, tiny minority even of the
ultrafidelista have ever heard pure Class A PP amp.
Well, I have, since that's about the only topology I use when building
tube amps.
I compared triode strapped JJ KT88s against NOS Philips XF4 EL34s,
also triode strapped in the same circuit, with somewhat reduced supply
voltage to not overstress the EL34s.
For me, the KT88s won hands down, even with the lower anode voltage.
I posted the circuit diagram some days ago in the "Step 2 for Fisher
Iron" thread.
You can still find it here, if you're interested:
http://img508.imageshack.us/img508/1751/wkschemod0.jpg
Unless one wants a SE amp, it doesn't get any simpler than that, I'm
afraid.
It could be simpler.
The 12BH7 driving triodes have about 3dB of applied series voltage NFB
from KT88 triode anodes to BH7 cathodes via the 300k/1k5 networks.
This means the anode resistance of the KT88 is effectively reduced from
about 1k to about 650 ohms, so thus compensating for the winding resistance
of the OPT
as seen at the secondary. But is this NFB really worth applying/
Its such a small amount, and around low µ triode outputs it doesn't do very
much.
But I agree that PP 6550 and KT88 and KT90 are splendiferous when triode
connected
and its difficult to have them sound bad.
And they are fine in SET based designs.
Patrick Turner.
--
"Due knot trussed yore spell chequer two fined awl miss steaks."