[Alex Kitic]

Zitat:Original geschrieben von Rumgucker

Hallo Alex,

Du kannst sogar noch einen Schritt weiter gehen und zusätzlich die Anodenspannung aus dem Halogentrafo gewinnen:





Ab: http://include.php?path=forum/showthread...ntries=527

I just wrote a very long post and found out that in the meantime I had to log again... did not copy my text in time, so now I am writing this short version.

I am glad that you do not consider the HF AC as some anathema. I am more interested in the AC side, as a means to heat directly heated tubes without audible hum and without resorting to DC which is not a perfect solution per se, as it causes a difference in potential across the filamentary cathode.

As for the high voltage schematics included, you should correct the DC output current - if coming from a 60W unit, it could be maximum 140mA due to the various losses in rectification (voltage doubler, approximately 0.31x the AC current, which I estimate at about 400mA, since the voltage is probably around 130V AC).

My solution includes two steps:
1) Added cap to improve rectification (much lower ripple) in the initial stage, at the input to the half-wave oscillator circuit.
2) Adjusted number of turns on the secondary (and the primary if need be) of the ferrite core output transformer of the unit.

A full fledged solution would include a regulator in front of the half-wave oscillator, to get a regulated DC voltage (thus a regulated AC output) and get rid of all relevant ripple (a regulator will have additional -60dB ripple rejection).

[Bild: IMG_2610.JPG]

If you choose to add a transformer on the output AC side, you should get extremely clean (in terms of 50/100Hz ripple) DC output, because all the ripple would be from a 40-60kHz source, i.e. at 80-120kHz and the output would be regulated as well (due to the regulation of the initial DC that is in direct proportion to the AC output). Of course, regulating the DC in front of the half-wave circuit means a rather large increase of voltage at the output, approximately 1.40x probably. This means that the output of your added transformer would also be at higher voltage and you could probably adjust it to be around 300V without resorting to a doubler, hence getting even more output current...

But my main interest here at the moment is creating interest in the use of HF AC for direct heated tubes, as a promising solution that might one day become "the" best sounding alternative.