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Here we have an attempt at making something La maison de l'audiophile has made for years, ( this is acknoledged on Thorsten Loesch webpage )

I don't understand the choice for SV83 , (sponsored by Svetlana ? )

Suggested is upgrading to C3m from Siemens .

For such an experimented designer as Thorsten is , 12,5mA across an EL84 type tube is very little .There is 16mA anode current but 12,5mA cathode and my experience is that for good sound from an EL84 you need at least 25mA .

The screen regulation is far from optimal and the circuit should have quite some hum .

According to the designer it has very little hum after all the powersupplys are fine tuned .

Again i suggest removing all the capcitors around the EL84 screen supply and coupling the screen directly to the cathode using 1 capacitor . ( very similar mod as ultrapath )

But i havent tried it so i leave this as suggestions for experimentation .

An input resistor off 220K is very high .( i like 100K max but this is not a real issue )

I would also suggest that decoupling the ultra path way would be a big improvement and would encourage to use ( yep don't panic yet ) an electrolytic in parallell with the mkp in THIS case . ( improves the bass by tightening it further )

The ultra path would see the decoupling capacitors go from the cathode of the 300B to the + 420volts of the powersupply.see also my PSE KT88 design .