How are you sure that the A9 O.T. have airgap?
No doc around the manufacturer site and over internet.
It seems the same question comes up, again and again.
How many threads? Two of them currently.
Recently I purchased one of these Chinese amps. The version I purchased used EL34 tubes, no UL tap, but had Global Negative feedback taken from the OPT secondary.
There was plenty of inductance in the output transformers (OPT), but not nearly as much as it would be if the E and I laminations were interleaved (like for push pull outputs, no DC allowed).
Not to worry, the producers of these amps are not completely stupid, but want to save money by not having to interleave the E and I laminations. And there are other reasons to use an SE transformer.
1. Line up all the E laminations on one side of the coils, and then line up all the I laminations on the other side of the coils, and then place paper or other thin material between the laminations (the "air gap"). That is an SE transformer.
Takes DC real well. Takes less labor to line up the laminations.
2. Interleave the E laminations (E one direction, then E the other direction, alternating back and forth, back and forth, through the coils) and put an I lamination at the end of each E lamination, one by one. That is a Push Pull transformer. Takes lots of labor for getting the laminations lined up.
Pretend you are in charge of producing the output transformer for the Boyuu.
Which one will save labor ($$$)?
#1 or #2?
Pretend you are the producer and seller of the complete Boyuu kit.
Would you be willing to use output transformers that did Not have an air gap?
Do you care about customer reviews?
Do you care about customer returns?
Of course it is also true that there are not enough laminations to do high Watts output at 20 Hz. But what did you expect for an amplifier that cost less than one High-End Single Ended output transformer (and the heavy High-End transformer cost lots more to ship).
Worry gets you nowhere. Make measurements and see if you are satisfied. If not, replace the output transformer with a very expensive one.
How many threads? Two of them currently.
Recently I purchased one of these Chinese amps. The version I purchased used EL34 tubes, no UL tap, but had Global Negative feedback taken from the OPT secondary.
There was plenty of inductance in the output transformers (OPT), but not nearly as much as it would be if the E and I laminations were interleaved (like for push pull outputs, no DC allowed).
Not to worry, the producers of these amps are not completely stupid, but want to save money by not having to interleave the E and I laminations. And there are other reasons to use an SE transformer.
1. Line up all the E laminations on one side of the coils, and then line up all the I laminations on the other side of the coils, and then place paper or other thin material between the laminations (the "air gap"). That is an SE transformer.
Takes DC real well. Takes less labor to line up the laminations.
2. Interleave the E laminations (E one direction, then E the other direction, alternating back and forth, back and forth, through the coils) and put an I lamination at the end of each E lamination, one by one. That is a Push Pull transformer. Takes lots of labor for getting the laminations lined up.
Pretend you are in charge of producing the output transformer for the Boyuu.
Which one will save labor ($$$)?
#1 or #2?
Pretend you are the producer and seller of the complete Boyuu kit.
Would you be willing to use output transformers that did Not have an air gap?
Do you care about customer reviews?
Do you care about customer returns?
Of course it is also true that there are not enough laminations to do high Watts output at 20 Hz. But what did you expect for an amplifier that cost less than one High-End Single Ended output transformer (and the heavy High-End transformer cost lots more to ship).
Worry gets you nowhere. Make measurements and see if you are satisfied. If not, replace the output transformer with a very expensive one.
Some nice clear photos here. (my amp although I didn't build it). All I have done is ground the speaker 0v terminals and add 2 resistors between the heater circuit and 0v to kill the remaining hum. Happy with it now, sounds great.
http://www.thevalvemuseum.org/sdhc/articles/art-262.htm
http://www.thevalvemuseum.org/sdhc/articles/art-262.htm
Sorry, wrong link posted. Try this one (the other one is members only).
EL34-B Single Ended Stereo Amplifier
EL34-B Single Ended Stereo Amplifier
I must say this thread has been excellent and I have been persuaded to acquire this amp. From all of you I learnt where the weak(er) spots of this amp are and started my own experimentation.
Attached is the documented (PDF) result.
https://filedn.com/l7UsPK07cbB4Azv0FsTo1rH/A10 modifications.pdf
Attached is the documented (PDF) result.
https://filedn.com/l7UsPK07cbB4Azv0FsTo1rH/A10 modifications.pdf
Happy New Year everyone. I finally finished assembling the Boyuu A9. The amp works well but I think I have a defective 6N9P tube because on the 1st start there was a permanent noise on the left speaker. I reversed the 6N9P and the noise went through the right speaker. Also the volume potentiometer is of poor quality because it generates noise which disappears then reappears depending on its position. I'm going to change it to one: "ALPS". See you soon.
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Hello Everybody,
Been following intently on this forum and have for the most part wired up this amplifier.
The one question that still remains for me is how do I ground this. I will post a picture to get some sort of clarification on what I should do next.
Thanks.
Imgur: The magic of the Internet
Been following intently on this forum and have for the most part wired up this amplifier.
The one question that still remains for me is how do I ground this. I will post a picture to get some sort of clarification on what I should do next.
Thanks.
Imgur: The magic of the Internet
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Hello, personally I wired like this:
Picture 1: green wire=speakers,blue wire=0V power transformer,red wire=to the ground,yellow wire=input audio signal.
**All wires goes to the common ground point on PCB.**
**For connection of red and yellow wires see pictures 2 and 3**.
**For an overview see picture 4.**
PS: Note that 2 connection points are missing which are explained by: "gregas" on page 46 (#458) of this thread.
I hope my comment is not too confusing.
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So i am quite happy, except for a couple of issues.
1. I get super faint right channel, if i balance the channel all the way to the right and max out the volume i can hear the right side but it is very low not comparable to the left side. I have swapped both the pre amp tube and the power tube each on separate occasions to see if it was tube failure. It was the same on both tries.
2. I get what i guess would be considered a hum, however its more static and ringing than a hum. If the Volume is all the way down the noise is pretty prevalent. if i turn up the volume about 20 percent it almost goes away, more volume the noise returns and seems to get louder with the more volume applied. it does once again seem to cut off at 90%.
Any help would be most appreciated. Thanks.
1. I get super faint right channel, if i balance the channel all the way to the right and max out the volume i can hear the right side but it is very low not comparable to the left side. I have swapped both the pre amp tube and the power tube each on separate occasions to see if it was tube failure. It was the same on both tries.
2. I get what i guess would be considered a hum, however its more static and ringing than a hum. If the Volume is all the way down the noise is pretty prevalent. if i turn up the volume about 20 percent it almost goes away, more volume the noise returns and seems to get louder with the more volume applied. it does once again seem to cut off at 90%.
Any help would be most appreciated. Thanks.
Close but no cigar...
Hi all! I have built the Boyuu EL34 A9 tube amp kit now, and have a problem with the "big tube in the middle". It does not get hot. I have checked all the soldering and double checked the position of the R301 resistor (in the circuit diagram that came with the kit it says to connect it to pin 8, but from studying the pictures it seema to be connected to pin 2). Could it be that the tube itself is bad? I have not yet measured the voltages, but enclose a thermal image.
Hi all! I have built the Boyuu EL34 A9 tube amp kit now, and have a problem with the "big tube in the middle". It does not get hot. I have checked all the soldering and double checked the position of the R301 resistor (in the circuit diagram that came with the kit it says to connect it to pin 8, but from studying the pictures it seema to be connected to pin 2). Could it be that the tube itself is bad? I have not yet measured the voltages, but enclose a thermal image.
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@learn
Hello, I think also that there is a problem with the potentiometer and it may create a resistive ground loop caused by its poor insulation. That can explain why the hum varies with the cursor position.
A solution can be to create an insulation between the body of the potentiometer and the chassis, but it may be not easy.
Did you solved the problem with a better quality potentiometer?
Hello, I think also that there is a problem with the potentiometer and it may create a resistive ground loop caused by its poor insulation. That can explain why the hum varies with the cursor position.
A solution can be to create an insulation between the body of the potentiometer and the chassis, but it may be not easy.
Did you solved the problem with a better quality potentiometer?
I had the same problem, bad soldering to the heater filaments in the valve base cap. After 2 attempts at forcing solder up the legs of the valve base it is now working reliably. Check with a meter for continuity across the heater pins of the Rectifier tube or substitute a similar one.
Update to the build.
I bought an alps 27 100k pot. Was very hard to install had to modify the case slightly to get it in but it is installed. However weird thing is that the pot is somehow reversed, where the all the way right is where the volume starts and goes up counterclockwise. This though however fixed my right channel having little to no sound. now everything sounds balanced and awesome.
My only residing issue is the hum that still changes based on the position of the volume pot. I rearranged my grounding points and the hum has subsided some but it is still there. Can this amp be soundless if on with nothing playing or is that just a downside of tube amps?
Any insight would be most grateful. Thanks to everyone's input!
I bought an alps 27 100k pot. Was very hard to install had to modify the case slightly to get it in but it is installed. However weird thing is that the pot is somehow reversed, where the all the way right is where the volume starts and goes up counterclockwise. This though however fixed my right channel having little to no sound. now everything sounds balanced and awesome.
My only residing issue is the hum that still changes based on the position of the volume pot. I rearranged my grounding points and the hum has subsided some but it is still there. Can this amp be soundless if on with nothing playing or is that just a downside of tube amps?
Any insight would be most grateful. Thanks to everyone's input!
I had a similar issue and i realized that the lines from the transformer was not on the right pins. I went back through and soldered the lines correctly to the right pins and it worked. Might just be an oversight, bound to happen.