I fail to see how in any way the EL34 can have any effect on the standing DC conditions of the output stage. Its cap coupled.
Also, is it really true class A2?
Also, is it really true class A2?
The EL 34 cathode tells you the ground is considered 0V. Nothing else, just to be sure!
Yes it is class A2, the driving voltage at full power is approx. 300 Vp-p. How would you call it?
I just re-checked because you had me going with your weird explanation.
Come on man. Admit it. There is standing DC in the output stage? YES
It flows through the cathode of the output valve? YES
Current is equal in all parts of a series circuit? YES
The only exception here is the parallel conection of the OPT secondary and the nominally 8R speaker. Asuming a 0.2R secondary (a fairly good assumption) the speaker is 40 times this so dont worry about it too much.
Come on man. Admit it. There is standing DC in the output stage? YES
It flows through the cathode of the output valve? YES
Current is equal in all parts of a series circuit? YES
The only exception here is the parallel conection of the OPT secondary and the nominally 8R speaker. Asuming a 0.2R secondary (a fairly good assumption) the speaker is 40 times this so dont worry about it too much.
I have nothing to admit. The author states there is no offset and if you measure it it can be - in the real world - something very close to zero and much less tha you think (i.e. 30 mV). The full loop includes the feedback network.
This amplifier was the object of a couple of articles in Costruire HiFi some years ago. Later another designer came up exactly with your doubts and Aloia replied giving some explanations. I don't have the articles right now but I remember very well this fact.
Moreover 0.2R is rather high considering the OPT has no gap and is only 600R:6R. With only 500 turns for the primary - without gap - you get easily 8H (using a 32x32 mm EI core). This is enough to guarantee that the reactance is 10 times higher than 600R//Rp at 20Hz. The -3dB point is at 2Hz! Rather in the real amp the low end is mainly limited by the combination with 140 uF cap and the choke around 5-7 Hz.....
Thus the secondary will have 50 turns. Filling the full space of the former (half volume for the primary and half for the secondary is the solution for the minimum loss) you will have several windings in parallel (or series-parallel if using a smaller wire) for the secondary. The DC resistance is easily 0.05-0.07 R!
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Hi M.B.H, I think it has no choice to be anything other than A2, because according to the circuit diagram ( 6C33C Single-Ended 4 ) the bias point is -109.6 V with 282 V on the anode and 160mA current, which puts it almost off of the graph and above the max safe power section! Graph is on left of page 7 here: http://www.jogis-roehrenbude.de/Russian/6C33C/6C33C-B-6S33S-VExtendedDatasheetMB.pdf
You miss the point.
The point is that there is DC in the transformer and potential builders should be aware of this FACT. If you deny it then you risk misleading those that seek advice, which is not a good position to put yourself in.
This is not about "it sounds good" or "it does not sound good"; it is simply about establishing objective engineering facts so that others can understand, make a balanced judgement, and then decide for themselves if they wish to pursue the design.
🙂
I am talking about the real thing. You have no idea about the amp and the instructions. You just apply the Ohm's law to what you think is the loop....
Are you sure it really works as you think?
This is not a 300$ Chinese amp from Ebay!! You will get detailed instructions, full technical assistance and the claimed results. Step by step. The first step is getting the amp fully working with the secondary floating and no loop feedback. You really get 30 W RMS and it really sounds very good. This is what I know for sure. Unfortunately I could not follow the other steps....
In his replay-letter on the review the author stated (and still states) that there is no DC offset. Knowing Aloia through his articles, amplifiers and speakers I have no reason to doubt about it. The only issue that people have reported about this amp is that the service life of the 6C33 is not very long: about 1500-2000 hours.
I put the e-mail addresses so that everyone can write and get an answer.
If you don't like don't buy it. I simply don't care!
Hi Gordy,
Nice, I didnt bother to look at the curves. Hmmm, 40 odd watts at idle. It could be a fun and short life for the 6C33.
I am not sure I have seen cap coupled A2, AB2 etc. circuit before. I see the cap is large but?
Nice, I didnt bother to look at the curves. Hmmm, 40 odd watts at idle. It could be a fun and short life for the 6C33.
I am not sure I have seen cap coupled A2, AB2 etc. circuit before. I see the cap is large but?
45,
Ohms law is used fairly often when working with electricity.
No one is trying to put down the design in any way. Merely have a conversation about the merits or not of such a design.
Ohms law is used fairly often when working with electricity.
No one is trying to put down the design in any way. Merely have a conversation about the merits or not of such a design.
You are absolutely right! Here some of the documentation that Aloia shipped to me, include the small offset infos you are talking about (in yellow color evidence). Please note the data curve of the tubes. They are the data of my tubes, manually selected by himself. I have obscured my name in data curves.
Aloia is not a china reseller, but a serious and professional Master. No mystere or secrets in his works....
P.S. my 6C33 have sounded more then 2.000 hours and they are still in good condition. Kit bought in 1996
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Well I am not completely right!!
This is not what he wrote in the review Piero, about the offset the other guys were right.
Now I have to find the letter on CHF were he wrote the contrary!!
I thought he was using a parallel circuit (with subsonic low pass filter, i.e. working for the DC only) for the offset compensation as he does for the DC coupled preamplifier that has a little unbalance due to the asymmetric load of the differential stage.....
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Is it a particular transformer? It could be done easily with a particular type of transformer. However this does not seem to be the case.
Using a normal transformer without any compensation (i.e. a parallel feedback circuit that compares the input and output potential respect to the ground) you will have an offset. This is what he says in your instructions. He says that being the DC resistance of the speaker much higher than the DC resistance of the secondary there will be a very small amount of DC current through the speaker that will not affect the performance. If you measure the DC resistance of the secondary of your transformer you can calculate your offset. The offset is a voltage and is the same for the speaker and secondary. It is just the current that will divide according to the DC resistances.
This is not what he wrote in the review. I remember that another designer (maybe Chiomenti, I am not sure) made a comment about the offset and in the successive issue, writing about another subject, he ironically replied stating there was no offset. If you have the issues of Costruire HiFi where he presented this amplifier and the successive 4-5 issues you will find what I am talking about.
Cheers,
45
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OK great, so we at least agree there is an offset. It will be there no matter what crazy unobtanium output tranny you use. It will be there. The higher the DC resistance of the secondary the worse it will be.
Notice I used the words "DC resistance". There is no way that any feedback circuit interactions can affect the standing conditions. Its cap coupled, with the bias derived from a potential divider. This is also not recomended for the 6C33 because of trouble with drift(especially at high anode disipation). Have fun
This really is like trying to flog a dead horse.
Notice I used the words "DC resistance". There is no way that any feedback circuit interactions can affect the standing conditions. Its cap coupled, with the bias derived from a potential divider. This is also not recomended for the 6C33 because of trouble with drift(especially at high anode disipation). Have fun
This really is like trying to flog a dead horse.
I am sorry but here you are wrong. You can simply use a autotransformer! This is a common solution in 6C33 "OTL like" amps while this one is a parafeed.
That's why I was not so sure about the offset, having read the articles and seen & listened to this amp.....
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The supply capacitors and output capacitor are high voltage polipropilene caps for industrial use.
It's not trying to flog a dead horse. In fact you could explain how to get 30W RMS (without clipping) from one single 6C33 without dissipating more than 60W in any modulation condition (i.e. from zero to 30W output) using your own solution. I mean a real amp not chats......
In 13 years - since its presentation - nobody has be able to do it, in my knowledge.
If you knew Aloia you would be less arrogant. He is a guy who does not believe in patents and copyrights. He thinks that publishing his schematics is the best way to defend his own ideas. However there are always little tricks which are not shown and make a substantial difference in the real thing.
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In configuration A I don't think to be able to misure offset. Don't you?
Piero, it is quite obvious there is no offset in fig. a.
About the service life of 2000 hours: it is good amount of hours.
At end of service life the tube is still usable but you don't get the maximum performance. You will have less power for the same THD. However this is not 3W amplifier.....
Don't worry about it it is normal and even if you get 20-25W after 2000 hours it is fine and still better than any other 6C33 single ended amplifier!
If you look at much more expensive amplifiers like the Lamm ML2.1 they guarantee longer life but they are parallel single ended amplifiers!
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The power consumption is much higher because the filament dissipation is quite high for the 6C33 (approx. 40W). You have to get at least 5-6000 hours service life from the Lamm to be on par with the MSB! 😎
The maximum power output, before clipping, is only 20W for the Lamm....
Cheers,
45
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