Hello to France!

recently I stumbled over the following circuit of French origin:



I have some questions:

- Why is the input / control grid of the small signal triode called "sortie 2" = exit #2? Does that mean "from exit 2 of some preamplifier"?
- I suppose the real output is taken from the upper end of the output transformer secondary, at the point where cathode FB (via the 2k2 resistor) for the first stage is taken from. But there is no output marked as such?
- I suppose the marking "HP 3Ohm" near where I would put the output means a nominal secondary impedance of the OPT of 3 Ohms?
- If so, at that point, an estimated output power of, say, 2,7Watt, will generate a voltage swing of about 8Vpp across 3 ohms. Now, the same voltage swing will be superimposed on a (DC) cathode voltage of less than 2 Vdc - the feedback faktor must be extreme and I wonder if the biasing method is correct? Mustn´t the driver cathode be elevated "artificially" to allow for so much feedback voltage swing?
- Last but not least, if someone has the original article, I would be glad to know about the primary impedance of the OPT (per chance I have two OPTs that have an impedance of 5k2 and an UL tap at 25%) and the feed voltage at point "HT" (OPT primary B+ side), which probably is rather lowish (I would expect 230-240Vdc).

Thank you very much for your help!

Tom

Hallo Tom , das ist ein ganz tolles Schaltplan das wurde nicht von dem Autor nicht wiedergelesen Ja "sortie" bedeutet Ausgang obwohl dort "Eingang" des Verstärkers bleibt Ja Ausgang ist ein 3ohms AÜ. 2,5k bis 5,2k würden OK sein . Ua etwa 220v MfG Pierre

Hello Pierre,

thank you for your comments!



Actually, loadlines of even as high as 5k will look horrible on the UL plot you can find on my homepage, which has parameters quite close by (Ea=Eg2=230V, UL=20%), see: http://www.tubes.mynetcologne.de/roehren/daten/ecl82pentode_20ul_230v.pdf., or for Ea=Eg2=200V and UL=30%: http://www.tubes.mynetcologne.de/roehren/daten/ecl82pentode_30ul_200v.pdf.

At the given same operation condidions for the power stage except g1 bias voltage, EL84 would be much more appropiate and give much less distortion - at least on paper when toying with UL loadlines.

Maybe I am missing something, that is why I asked and why I am looking for the original article...

Tnx2u again!

Tom

Hallo Tom, wahrscheinlich wurde niemals die ECL82 dafür entwickelt
As many other DIYers here and there , try a really regulated PSU for G2 and you'll hear how sweet is the sound of the real TETRODE or PENTODE mode . Did you follow this very thread on DIYAUDIO ? The UL mode was intended for cost killers MfG PIerre

Hello Pierre,



Definitely not, indeed.



Usually (in most cases), it is not what I would call "sweet" in any regard although stabilizing Vg2 does help in many regards, no doubt about it.



In my book under work, there are about two pages full of arguments contra SE UL and about two lines of arguments pro SE UL. The ratio switches over by 180 degrees when arguing about PP UL, at least when using class A1 or AB1 and comparing to straight pentode PP of the same class.

Regards,

Tom

Hallo Tom , this is an OT to the ECL82 question but i've seen your experiments with EC91 on Geek I'm not registred there but would ask you if you ever tried , in the original SRPP , as upper tube , the EF184 trioded (g2+g3+A) ? Thats' what i made and confirm your point of view With lots of capacitors , the mu-stage is not so perfect ... I get 100v PtoP on 60kohms with 400kHz bandwidth effortless