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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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18th Jan 2012, 2:46 pm | #41 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
Posts: 617
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Re: My first experience with electronic tubes
Yesterday, I tested my EL84's. They seem to be OK. Following cmjones01 advice, I mounted the valves in a socket previously prepared with the circuit I pretend to build.
Even a third valve that I have with the exhaust tip broken, it's good I think. Using 230Vcc I measured the following values of plate current: No.1 38 mA No.2 35 mA No.3 (broken tip) 32 mA Is that enough for the EL84 operation? I also have two 6П43П valves. They are power pentodes with the same pinout than EL84. I tested them too, but I stop when they reach 85 mA. I think that is too much for a valve like that. I guess they are for a smaller VCC, but I couldn't find any datasheet of them. What do you think? PS: The only problem was to remove the valves from the socket, they were really hot. I had to wait almost 10 minutes after each test to remove them.
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19th Jan 2012, 5:26 pm | #42 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
My EM80 is good too!!!
I tested it yesterday and it worked nicely. The 6П43П that I mentioned in the last post, are EL86 equivalents. I found it in a russian page. This is going OK
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23rd Jan 2012, 6:31 pm | #43 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
I mounted the output stage of the amplifier and tested with a signal from a radio. It works. I'm very happy with this. The output signal was not too strong, because the input signal was weak.
Of course I think that when I mount the pre-amplifier it will work much better. PD: Is "to mount" a suitable verb for connect all the components according to the diagram in order to make it work.? I have my doubts on that.
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23rd Jan 2012, 8:41 pm | #44 |
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Re: My first experience with electronic tubes
The way I use 'mount, mounted' is for individual components, 'build, built' would have been better for a number of components assembled to make a unit. But as english is such a mixture of languages 'mounted' was fully understood.
P.S. I love your 'strap line' "There's nothing you can do that can't be done."... so true! |
23rd Jan 2012, 8:59 pm | #45 | |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
Posts: 617
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Re: My first experience with electronic tubes
Quote:
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23rd Jan 2012, 10:04 pm | #46 |
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Re: My first experience with electronic tubes
I have just built this https://www.vintage-radio.net/forum/...ad.php?t=78559 it works very well, super things these valves.
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23rd Jan 2012, 10:25 pm | #47 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
Excelent merlinmaxwell !
Congratulations on a well done job. I almost envy you (in the good way) I hope that my amplifier looks so good when I finish it. The cabinet I will use is a Czeck-made one. I have several of this cabinets that can be reduced at will by cutting their pieces properly. Is the same kind of cabinet I used in the equipment I showed in my album. On the other side I won't let the valves exposed, I don't like that because I don't have enough valves for replacement. And, on the other hand, my wife is a compulsive cleaner, and I want to protect the valves from her duster. I intend to build a closed cabinet with all component inside. Of course, it will have enough ventilation on top and bottom.
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27th Jan 2012, 2:42 pm | #48 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
I was testing the bias of the valve 6Н1П in order to use it instead of 6Н2П. I need your opinions regarding the parameter values that I think to use
First stage: HT=210V Vp=150V Vc=3V Ip=1,66mA Rp=33K Rc=1,8K Rg=470K Second stage: HT=210V Vp=150V Vc=4V Ip=1,2mA Rp=60K Rc=3,3K Rg=470K Everything was by "trial and error" method in part because I don't have any decent chart (Ip vs VP) for the 6Н1П. It seems good to my basic knowledge but I have some doubts: ¿Are those small currents suitable for the amplification? I think in the first stage there would be no problem, because if I inject a signal of, let's say, 150mVrms, and havin a gain of 15 - 16 (amplification factor for 6Н1П is 33, I think reduce it to a half would be expected for this circuit, any opinion welcome), in the grid of the next stage ther would be 2,25Vrms. This second stage has its cathode at 4V so, I guess there wouldn't be saturation. But the second stage will amplify this signal, let's say 15 to 16 factor, and I will obtain in the EL84 grid about 33Vrms. If the cathode of EL84 is at 5V it will saturate. I do not want saturation, this is not a guitar amplifier but audio amplifier. I don't know if I have explained my self well and I hope you had not slept with my wording , but I'd like to know your opinions regardind this. Any help welcome. Yours Miguel.
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2nd Feb 2012, 8:42 pm | #49 |
Heptode
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Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
Reconnecting properly the windings in the TC-180 mains transformer, I obtained 265V HT. That gave a plate voltage of 255V, and a plate current of 49-50 mA. The cathode voltage increased to 6,5V. I guess that with these values the EL84 (6P14P) would amplify a little more.
This is getting better. Let's wait that neighbours don't demand me.
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3rd Feb 2012, 7:46 pm | #50 |
Heptode
Join Date: Dec 2011
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Re: My first experience with electronic tubes
Excelent!!
The amplifier sounds wery well. It begins to saturate when the sound level is bothering inside the room. I will not reach that level in normal use. I'm very glad with the result. I will try to take some pictures to post them here. It is just an "air mounting" for test but it worked. I found that the 6N1P has nothing in common with the datasheets shown in the web. I couldn't obtain the bias point they recommend for that valve. Using a resistance decade box in the cathode and another in the plate, I adjusted the bias trying to reach the values given in the datasheets. This is what I got: HT=255V Vp=107V Ip=2,5mA Rp=68K Vc=2,5V Rc=1K
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9th Feb 2012, 5:51 pm | #51 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
I mounted a 7,5V Zener diode instead of the 120ohms resistor in the EL85 cathode. I thought that the plate current would decrease but it remains at 50mA (more or less). With the 120 ohms resistor the grid voltage was -6.5V and now is -7.5V.
Is this fixed bias? I don't like to mix solid state component with valves because as my first project with valves I would like to make it pure-valved, but anyway I'm using silicon rectifiers so, why not.
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13th Feb 2012, 6:02 pm | #52 |
Heptode
Join Date: Dec 2011
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Re: My first experience with electronic tubes
Althought (saddly) this thread has almost become a monologue, I will keep sharing with you my first experience with valves.
I removed the Zener diode and kept the 120 ohm resistor. A friend told me that if the Zener diode blow out it could take the EL84 with it. That would be very sad for me. I tested 6N2P (a friend gave one of them) instead of 6N1P. I sincerely prefer the later. The 6N2P (12AX7, ECC83) has a better bass response. It feels like a hammer hitting my ears when the speaker goes forward, but the 6N1P (ECC88) has a flatter frequency response. Despite that 6N1P has lesser bass response it has enough bass for me. I like it and I will keep it in the design. The other thing is that I will supress one of the triode stages. Ony one 6N1P triode provides enough amplification to drive the EL84. So, now I think I'm goint to build a stereo set using a couple of EL84 (one for each channel) and a single 6N1P triode to drive each pentode, then I will only need one 6N1P. The final design will have three valves for amplification (a couple of EL84 and one 6N1P); and the EM80 magic eye. Anyway I will think in future, and I will build a chassis which will allow me to make future improvement. For the output I will make holes for a couple of octal sockets for each stage. I will put noval sockets for EL84 in that holes that would be easily replaced by octal ones if I get a more powerful valve. Now I will only use one noval but I will pretend to make a push-pull if I get matched EL84) When I'll finish it you will see plenty of empty holes in it. Hope to take some pictures this week of my "freak" amplifier. (Actually the device I develop to obtain a final design)
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15th Feb 2012, 9:20 pm | #53 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
Here some pictures I took to the "thing" I have built to test the circuit and to learn a little about valves. Before this, I knew nothing about valves, now I know something at best. It really looks awful, but that is just a test device. , I pretend that the final cabinet and the chassis look much better. I have some experience with cabinets.
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15th Feb 2012, 9:22 pm | #54 |
Heptode
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Re: My first experience with electronic tubes
More pictures
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15th Feb 2012, 9:26 pm | #55 |
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Re: My first experience with electronic tubes
I would stick to the cathode resistor for bias, it automatically adjusts the current. Simple and elegant, just like valves. My 3-3 is still going well, I am listening to it now.
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15th Feb 2012, 10:21 pm | #56 | |
Dekatron
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Re: My first experience with electronic tubes
Quote:
When Zener diodes fail, they tend to fail short-circuit - and this would effectively give zero bias. Then, the EL84 would draw lots of current. A resistor will also give some compensation for variations between valves - a valve which draws more current will receive more bias, thus reducing current slightly. A Zener diode will give the same bias under all conditions. |
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15th Feb 2012, 10:35 pm | #57 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
Got it. I replaced the Zener diode by the 120 ohms resistor. You can see them in the pictures in the cathode of both EL84's.
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27th Feb 2012, 3:18 pm | #58 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
Well, now I have four 8 ohms speakers, and I was thinking how to solve the problem of impedances. This is what I did.
I connected a couple of EL84 with their respective output transformers in parallel, supplying them with the same input signal, and then I connect the output windings in series. That will duplicate the output voltage, then I connect two speakers in series (16 ohms) and it worked very good (for my ears). I will need 4 EL84 (by now I only have three and one in the way) to make a stereo, but I think that they do not need to be matched because they are not in push-pull, they just add one to each other. Yesterday I was listening music with that configuration. Is that OK, or is it just another Miguelism?
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27th Feb 2012, 3:57 pm | #59 |
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Re: My first experience with electronic tubes
It isn't completely clear what you have done here. Could you draw a simplified circuit diagram / schematic?
Speaker impedence matching is not as critical as many people think. A moderate impedence mismatch will cause the output valve to work less efficiently with less output, but the performace is usually adequate. |
27th Feb 2012, 4:37 pm | #60 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
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Re: My first experience with electronic tubes
Sorry Paul. I tried to explain what I did to a fellow in Spanish, and he told me the same. Imagine in English. This is what I did.
Let me ask another question. I began to cut metal to built the chassis and the cabinet. Should I include the posibility to mount transformers or even the valves sheets (valves sockets will be in an independent aluminium sheet) on rubber washers?
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When electrons move, things happen. There's nothing you can do that can't be done. Last edited by Miguel Lopez; 27th Feb 2012 at 4:49 pm. |