Dear Euro21, thank you but I am not sure if I understood you correctly. Do you mean that all what I should do is to adjust the R-GK value to get 82V on the grid of the E80F, and that is it?
Dear Tom, thank you so much for answering. The reason for using the E80F is (you can laugh😊) that my intention is to recycle an old power supply made by your compatriot brand Zeiss. It is a tube power supply for the deuterium lamp of a microscope. It has two Valvo PL36 tubes and the E80F, with the main transformer with the 6V and 25V secondary windings for the filaments and the secondary winding that gives 350V when rectified. Perfect for the project.
Out of curiosity, there is also a circuit with a tube voltage regulator that gives, what a coincidence, 82V; but I can’t keep it for the grid of the driver because I could not have the designed feedback anymore.
If you will be so kind to check, when you can, if the E80F is suitable (I am not so good for that) then it’s fine, but if not, no problem at all, I will buy two EF95.
Thank you so much!
Giovanni
Dear Tom, thank you so much for answering. The reason for using the E80F is (you can laugh😊) that my intention is to recycle an old power supply made by your compatriot brand Zeiss. It is a tube power supply for the deuterium lamp of a microscope. It has two Valvo PL36 tubes and the E80F, with the main transformer with the 6V and 25V secondary windings for the filaments and the secondary winding that gives 350V when rectified. Perfect for the project.
Out of curiosity, there is also a circuit with a tube voltage regulator that gives, what a coincidence, 82V; but I can’t keep it for the grid of the driver because I could not have the designed feedback anymore.
If you will be so kind to check, when you can, if the E80F is suitable (I am not so good for that) then it’s fine, but if not, no problem at all, I will buy two EF95.
Thank you so much!
Giovanni
Dear euro21, I see now that you have posted a complete simulation while I was writing my answer. Is there a reason for not having inputed all the same values of original Tom's wiring diagram?
The e80f tube is not really suitable for driving Pl36, with a mu folower ecc81 driver you can get superior peerformants as we showed in a previous post
Dear Marius, thank you.
what I wanted to know is if the E80F is suitable or not for correctly driving the PL36. If not, then I think that I will stay with the EF95 of the original diagram, because I do not need of much power, I only use high efficiency speakers.
what I wanted to know is if the E80F is suitable or not for correctly driving the PL36. If not, then I think that I will stay with the EF95 of the original diagram, because I do not need of much power, I only use high efficiency speakers.
By some googling I found the originally used OPT is still available, search for "ATRA0288", reflected impedance being 5k2 nominally.
Kind regards, Tom
It shows how the E80F VAS stage can connect to EL36 output stage.
The actual values depends on several parameters (B+ voltage, OPT parameters, EL36 operating point /depends on B+/ etc.).
For example possible LF behaviour (mostly bump at few Hz due to the OPT) determine the C1, C2, C3 values.
Tom tested its, his values applies to for the tools he uses (tubes, transformer, PSU).
If you change something (for example another VAS stage), need to rethink other values too.
Hi Giovanni, as popa marius has already noted, the E80F (hi quality EF86) is not an ideal candidate at this point. The circuits presented by him and mine from the beginning of this post will probably deliver better results. Both EL183 and 6E6P, 6E5P are dirt cheap. Fixed bias of the PL36 reduces the thermal load (cathode resistor) and increases output power.
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Dear Pieroh, thank you but I am already on the way with Tom's project. I ahve ordered the tubes and the output transformers.
As said, I do not need of much power because I use high efficiency old speakers. To give an idea, I have built years ago a single ended amp based on the 807 tube and in normal listening the volume pot is at 1/3 only.
Kind regards
Giovanni
As said, I do not need of much power because I use high efficiency old speakers. To give an idea, I have built years ago a single ended amp based on the 807 tube and in normal listening the volume pot is at 1/3 only.
Kind regards
Giovanni
Hi Giovanni, just try it out. When not satisfied you can easily change the driver tube and the few resistors around. I will try Tom's feedback scheme (Anode of PL36 to G2 of the driver) in my amplifier.
Dear Pieroh, will see. By now I will start with Tom's project, everything is on the way.
Dear Tom, could you please post the +B set up, I mean the drawing of resistors and capacitors and related values after the diode bridge?
Thank you very much
Giovanni
Dear Tom, could you please post the +B set up, I mean the drawing of resistors and capacitors and related values after the diode bridge?
Thank you very much
Giovanni
Another builder who might be an inspiration: https://www.inner-magazines.com/audiophilia/revenge-el-pl36-se-amp/
Dear Pieroh, thank you. I stumbled on that page before, but the guy is not showing the wiring diagram.
After finding this thread here inn diyAudio, I found many similariries to what is said there and what said by Tom here.
Kind regards
Giovanni
After finding this thread here inn diyAudio, I found many similariries to what is said there and what said by Tom here.
Kind regards
Giovanni
Dear Tom, an update.
First at all, thank you for your project. I have finish everything.
Unfortunately, I can’t add any graph because my audio wave generator is off and I am waiting for a new one that I have ordered. But in the meantime, I must say that the sound is just magic.
My amp is a bit less efficient than your one because I have lower voltages. To give a figure, at the plate of the Pl36 I have 320V instead of 350. I do not think that the change of the operation point will be relevant because of that. And I do not need much power because I use high efficiency speakers.
For the record, I must say that at the beginning I become crazy because of an important interference among the output power tubes, a lot of strong noises. Displacing the transformers was not effective at all, until I found that the noise was sensitive even to the hands: the noise was decreasing significantly just by moving the hands closer to the output tubes.
The final solution was a metal shield, a small tube made by a metal mesh, on either one of the two Pl36. It is not important on which of them, by shielding one of the tubes the amp is totally quiet.
I have not found a reason for that, the only thing that I suspect is a mutual interference between the two tubes.
Are you aware of a particular sensitivity of the tubes under this point of view? The space among the two tubes is 4 cm only.
Giovanni
First at all, thank you for your project. I have finish everything.
Unfortunately, I can’t add any graph because my audio wave generator is off and I am waiting for a new one that I have ordered. But in the meantime, I must say that the sound is just magic.
My amp is a bit less efficient than your one because I have lower voltages. To give a figure, at the plate of the Pl36 I have 320V instead of 350. I do not think that the change of the operation point will be relevant because of that. And I do not need much power because I use high efficiency speakers.
For the record, I must say that at the beginning I become crazy because of an important interference among the output power tubes, a lot of strong noises. Displacing the transformers was not effective at all, until I found that the noise was sensitive even to the hands: the noise was decreasing significantly just by moving the hands closer to the output tubes.
The final solution was a metal shield, a small tube made by a metal mesh, on either one of the two Pl36. It is not important on which of them, by shielding one of the tubes the amp is totally quiet.
I have not found a reason for that, the only thing that I suspect is a mutual interference between the two tubes.
Are you aware of a particular sensitivity of the tubes under this point of view? The space among the two tubes is 4 cm only.
Giovanni
Based on your description the amplifier has parasitic oscillations, probably in the tens of megaherz range if moving your hand around affect it.
Thread 'Oscillation in tube amps' https://www.diyaudio.com/community/threads/oscillation-in-tube-amps.145103/
Thread 'Oscillation in tube amps' https://www.diyaudio.com/community/threads/oscillation-in-tube-amps.145103/
Thank you very much! It is a long thread and I will read it carefully, but surely it will be very interesting. For example, in the first page it is said that parasitic oscillations are more common with positive feedback, which is the case of this amplifier.
I forgot to say that I have not implemented the Zobel network on the primary of the output transformer. Should it be better to have it?
Kind regards
Giovanni
I forgot to say that I have not implemented the Zobel network on the primary of the output transformer. Should it be better to have it?
Kind regards
Giovanni