mon soucis de tension ne viendrait 'il pas des condensateurs qui auraient une trop forte resistance serie?
peut t'on abaisser cette resistance avec un condo poly en parrallele.
cdlt
christian

les 8uf de l'alim, ils sont assez ancien

Donc le ronflement concerne les étages avant le volume.

magnétic 6000 ohm, prise à 43%. 35w
christian

"Optimised?"

Using a 43% lower DC screen voltage will just get you less power output like the triode case. (or a lot of distortion if power is not reduced)

My working hypothesis (working on data measurements to verify this yet) is that the "magic" 43% tap is just the point where screen grid current distortion (using B+ DC on the screens) = the 3/2 power law plate current distortion component, due to a low load impedance. Since they are out of phase they cancel largely. The 43% figure is specific to tube construction (mainly screen grid spacing or equiv. triode configured Mu), so will vary with tube. Nothing magic about 43%.

The effect of the screen current distortion is to syphon off plate current when plate voltage is lower than the screen V. (it is put back into the xfmr primary at a less effective tap) This effectively rounds off the usuall pentode knees in the curves on the left side. A load line then has near equal spacing of plate curves crossing it, effectively eliminating the usual 3/2 power inflation of the curves at high current.

Using a tertiary winding to reduce the DC screen voltage will eliminate the large screen current distortion component leaving one with an un-cancelled large 3/2 power plate distortion at the same power. So power output has to be reduced (back to triode level) to eliminate this high plate distortion.

Screen current distortion is a voltage output dependant factor (and a DC screen V factor). Plate current 3/2 power law distortion is a current output dependant factor (and load Z factor). When a real speaker is connected, inductive reactance will cause voltage and current to go out of phase, and the two distortion components will no longer cancel. So UL tests great on the test bench with a dummy load, but falls flat with most real speakers.

UL was just a marketing trick. There is however some hope that it can be fixed.

Don

__________________
Levitating moments: http://xxx.lanl.gov/abs/gr-qc/0610015 0607086 ...

Bonsoir.
Moi j'aimerais savoir pourquoi (et si possible en Français) pourquoi aux yeux de certains l'ultra linéaire est sujet a caution.
Le gros problème de l'ultra linéaire est la plupart du temps la mauvaise qualité du transfo (ou le mauvais bobinage de celui ci ce qui revient au même).
Les bons transfos ultra linéaires avec des prises écrans judicieusement placées ne sont pas légion ....et j'ajouterai surtout de nos jours.... a part quelques exceptions généralement venues d'ailleurs.
gege 94