Really good video with excellent explanation

Your work is excellent. This is how technical videos on tube amplifier design and build should be. Thanks for making such a big effort and SHARING here with all Keep up this great work !! Warm regards from India!

@MrVideoTronix

3 жыл бұрын

Thanks for this comment! I appreciate it very much :)

Ah the ECL86, a classic tube used in many things from TVs to Tape recorders etc. I would say the values for this circuit are so general I already knew every value you calculated in my head. I would however say you don´t want to go higher than 470K on the input especially when using modern audio sources with it as it will introduce distorsion and stuff pretty easy on many devices plus increase noise level etc otherwise so it was a good pick. I would probably use a bypass capacitor on the first stage cathode too when using a single stage pre-amp to increase gain and response in lower end, you can actually substitute the grid resistor and cap all together on the triode and use a LED of your choice to bias the tube, as the voltage drop is constant you bias the tube to the LED voltage drop but won´t limit the current as a LED act like a diode when it conduct and you don´t lose gain because of it. and as you say negative feedback is good to control the sharp high end as well, I always put a 12K resistor in series with a 100K pot for the feedback to make it adjustable. but I would not combine negative feedback with LED Bias though. but I often include a 100-500K pot in series with a 0,1-1uf capacitor to ground to the grid side of the second stage in your case pentode grid, this gives you a nifty tone control that can depending on the cap size cut higher end sound gain and still keep the bass in the bottom for a much more balanced sound, and I likely use a 220K resistor to ground together with that pentode grid too. in many designs it was often a small value capacitor in parallell of the primary winding on the output transformer, this cap cuts high end sound by filtering it out from the transformer completely if you so desire

@antonioroccuzzo4214

5 ай бұрын

👍👍👍👍👍👍 I agree with you. My First amplifier made at school when I study electronic, was done with ECL 86, It was 1970. I Remember that my teacher sed that classe A Is polarize in the middle of the straight part of the triode's curve. To me, looks that the negative voltage Is to High and tube Will work in classe B (at the begin of the straight part of the curve) . Class B Is used fo push pool amplifier, single tube will add a distortion on the negative parte of the sine wave. Unless he Is not projecting an amplifier for a distorted guitar. True Is that a bass and treble control would not be a bad idea. At the end, adding a tone controllo are 4 capacitor 5 resistors and 2 pots. And as you sead, an input attenuator should be used for nowdays signal. 👍👍👍👍👍👍

@Pulverrostmannen

5 ай бұрын

@@antonioroccuzzo4214 Indeed. The Bias is often overlooked and people like to bias them too cold and it affects the dynamics of the audio. I have typically used a simpler EQ solution in my amps that has it. It is a combination of Negative feedback (with selectable) bypass capacitors and a low pass filter using a capacitor and potentiometer in the pre-amp stage. I had good results from this. In my biggest amp which is a dual mono Class A EL34 I can also pick different Bias resistances and I have a very special home made power supply that I can adjust voltage from 240-500 Volts that have perfect DC output, no ripple. Clean enough to inject to the amp without any filters. I usually bias these tubes very warm to a point they even redplate a bit but the audio is incredible then. Typically I run these tubes at about 150MA each in true triode mode which gives me pretty much output power. I still get long life out of the tubes anyway and the power is also dynamic with special controls I have included that reduces the tube voltage when nothing is playing. Good stuff

You would get better base response if you added a bypass capacitor to the triode cathode resister.

Interesting tube and straight forward explanation. Nice drawing skills, too.

@MrVideoTronix

2 жыл бұрын

Thank you for your comment! I am happy that it was interesting for you and that you like my drawing skills. 😊

The magic of NFB .hiding the problems on the bench and ruining the music ....

Well nothing special about the ECL86 it is a simple triode-pentode there where more than 30 tubes of this type in the day. They where used in almost every record player that was coming out of EU land in the late 50s and 60s so I guess the really special part is they are very cheap an quite easy to pick up as NOS. They do produce good sound and I have I worked with them myself the only problem I see with them they really only work with older crystal head turntables that put out a a higher voltage than the 100~300mv from a electromagnetic head. I did try and make a guitar amp but again not enough gain from the single Triode to make it a viable project. Good job on explaining how to compute grid voltage that is the way it was originally computed and was just common knowledge of the day now mostly lost, Thankfully an old RF engineer from my radio club explained this method too me ;) Many of the so called modern 'Tube' experts get it 100 wrong.

Great explanation, I have just worked with small jfets and I can see is almost the same way to bias a tube amp. I must ask, why did you choose exactly1,2mA 36mA for anodes bias?. I can see the mA values are not exactly at the middle of the graph which I always thought would be the best point to bias a jfet / tube.

❤

Of by the way you where getting distortion because you did not match the ECL82 to the output. Ideal is an 8ohm speaker and transformer though you can also use down to 5 with some component adjustment. Will have to watch the next video to see what you did to fix this.

Great video. I was surprised how good the response was without the transformer. How did you come up with the initial current values for the tubes? Did the output from the triode factor into the values you picked for the 2nd tube? I was excited to see that we have the same multimeter! I bought mine used 15 years ago and it has seen a lot of use. I did have to open it up and clean the power switch but other than that it has been great. Keep up the good work.

@MrVideoTronix

2 жыл бұрын

The only purpose of the transformer is to transform the low impedance of the loudspeaker to a much higher impedance seen by the tube. Therefore a resistor with high resistance will work perfectly. The value of the bias current for the pentode depends on its load. You have to pick a current which allows the tube to have maximum voltage swing in the positive and negative direction. The minimum current flowing to the tube is of course 0mA. So if set the bias current is 36mA (and the amp is class A) the maximum negative current swing is 36mA. For the positive current swing, it can conduct more current in this case the maximum useful amount of current would be 72mA (36mA x 2) to have a symmetric swing. The transformer and loudspeaker that I have used gives me an impedance of about 8000Ohms on the tube side. Since I have a supply voltage of 250V available and a want symmetric swing 36mA is right because 250V / 8000Ohms = 31.25mA (near and below 36mA). So there is enough bias current that a complete negative current swing (31.25mA) is possible. Keep in mind that this is possible if the load is coupled with the transformer since the transformer has (almost) no DC drop the downswing can be as big as the supply voltage and the Impedance allows. The same applies to the upswing of course. You also have to keep in mind that you don't exceed the maximum power dissipation rating of the tube. For the test with the resistor, I head to use a 4700Ohm resistor (about 8000Ohm / 2) because the resistor will have a DC drop and the voltage on the resistor will be 4700Ohm x 36mA = 169.2V. If the resistor would be 8000Ohms no voltage swing would be possible because it would already have the full supply voltage on it in the bias condition. The selection of the triode bias depends on the anode resistor here you might also aim for a symmetric swing (or at least no clipping at maximum output) you want to set the current to a value that gives you half the operating voltage of the triode on it's anode resistor. The gain of the triode also depends on the value of the anode resistor. So you try to get the optimum for your application. And this brings us to the next answer. Yes, the output of the triode factors in the values of the pentode. You look at the gain of your stages and estimate your input signal. With this information, you need to make sure that you have enough gain to get the maximum output. Great that you have the same multimeter! It's a pretty good multimeter. I had to clean the power button and function buttons a while ago.

@RobsFixitShop

2 жыл бұрын

@@MrVideoTronix That makes sense, thanks for the great explanation!

@MrVideoTronix

2 жыл бұрын

@@RobsFixitShop You are welcome!

Salve, vorrei sapere se hai usato un trasformatore di isolamento oppure hai staccato la messa a terra dell'oscilloscopio? Saluti Francesco

very interesting, i know pcl86 was a tv audio amp tube and quite cheap. any chance you could do a point to point picture with values of components drawn on and a schematic, its exactly what i would like to run my old garrard turntable. thanyou in advance, hi from scotland :)

@MrVideoTronix

2 жыл бұрын

Hi! I am happy, that you enjoyed my video. :) Please use the schematic you can find in the 2nd part of my video series kzread.info/dash/bejne/pWF6o6WJgcy4d5c.html The schematic can be seen at 9:21. Here are the values: Supply voltage = 250V Rgt = 470k (1/4W) Rkt = 1.5k (1/4W) Rat = 100k (1/4W) Rgp = 470k (1/4W) Rkp = 180 (1/2W) Rfb = 220k (1/4W) Rg2p = 2.2k (2W) Cfb (the capacitor connected to Rfb) = 22µF (300V) Cgp = 100nF (300V) Cgt = 100nF (300V) Ckp = 470µF (25V) Transformer: use a Transformer with an input impedance of about 5kOhms and an output Impedance that matches your loudspeaker. Add one extra 22µF capacitor between the supply voltage and ground to stabilize the supply voltage. I hope you have a lot of fun assembling it!

@lookoutleo

2 жыл бұрын

@@MrVideoTronix can you put one together on a piece of board and I'll pay you for parts and doing it :)

@MrVideoTronix

2 жыл бұрын

@@lookoutleo ​Yes, I can put one together for you. :) If you are interested, please write me an e-mail to discuss the details. You can find my mail address under the about tab of my channel.

The heart of the amplifier it the output transformer, if the transformer is not design for SE amplifier don't brother to build SE tube amps period. Difrent core topolgy and core material different from AC power transformer !!!.

@frankgeeraerts6243

9 ай бұрын

Yeap ,that's right and .............other design flaws .....masked by NFB........operation conditions on datasheets only ...this tube won't live long .

😂😂😂😂😂😂😂