looking for schematic; three EL84's in PSE ?

[Empee]

Dear all,


Has anyone got a schematic for three EL84's in PSE ?

The highest-end the better, but no ultra-linear schem's please
since my OPT's got no taps for UL


Cheers,

Empee

[the_manta]

Well, no problem.
You can use any SE schematic with the EL84.
transconductance will triple
optimal load resistance will only be a third (5,2K/3 ~ 1,7K)
µ remains the same

because all capacities will triple it is better to look for a schematic with a more powerful driver stage. A EF86 with 1M load is probably a bit weak.

regards, Simon

[Empee]

OK!

But what if I were to tripple this design,
what would happen with the value of the shared Rfb resistor ?


Cheers,

Empee

[the_manta]

Hi !
This is a nice schematic !
ECC81 sounds IMHO better than a ECC82 or 83. And the µ=60 isn't too much or less.

I forgot one thing in my last post !
If you have automatic bias with cathode resistors, than you also have to use only a third of the value. That's logical, because the voltage which drops on that resistor must be same whether with one or with 3 or more tubes. But when you use 3 tubes, the current triples. So you can only use a third of the resistor value to get the same voltage as with one tube. In your schematic, you would use 270/3 = 90 Ohms.

A still better way is to use three single 270 Ohm resistors incl. cap
for each cathode of the tubes. This protects you from current-drifting of the tubes and guarantees that each tube gets the same amount of current.

And yes, you can leave the feedback unchanged ! Because this a so called "Voltage controlled current feedback" Each voltage change in the Output Tubes Anode will be sent back and lies in parallel with the signal voltage on the grid.
Since we don't change any voltage levels if we use three tubes (we only triple the current) and the feedback is voltage controlled, we can leave it unchanged.
Only a "Current controlled .......... feedback" would need a modification.

Well, I hope I could help you.
Nice circuit. Because the Output transformer is not integrated in the feedback loop, you won't feedback any iron-distortion produced there. A real difference in sound, typical warm and smooth.

Regards, Simon

[Empee]

Jeez'

thank you very much for the explanation for every issue!

helps a lot in learning


The design is by mr. Alex Kitic,
made the SE version and it perfoms beautifully!

but with the less efficient speakers,
I really need some more powerrrrrrr.....


cheers,

Empee