• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Boyuu EL34 A9 Tube Amp

Hi all

I'm new on here and I'm hoping someone can help me. I bought (maybe foolishly) a Boyuu EL34 A9 amplifier as a kit. I'm used to building electronic kits with good plans but the Boyuu comes with a schematic wiring diagram only which I'm finding difficult to interpret. There are very few photos of the internal wiring of the A9 availalbe. My main problem is the connections to the two front pots; then the rear input/output panel and, importantly, the mains input.

Does anyone have the ability to post/send photos of the inside of one of these amps? Or does anyone know someone that can build it for me for a fee?

Thanks in appreciation of some help.

P
 
Can you post some pictures, especially of the schematic?

Where are you located? If you want in-person help or somebody to build it for you, that would help.

It might be cheaper to sell the kit on to another user, and just buy a pre-built amp.

However, from what I saw with Google Image search (in 30 seconds), it doesn't look like a very complex circuit. You can learn how to read (and build from) a schematic, with a bit of work. So don't give up!
 
I'm new on here and I'm hoping someone can help me.
Hi I brought some months back from china a voltage amplification tube: 6N9PJ × 2.
power output tube: Shuguang EL34B × 2.
rectifier tube: 5Z3PJ × 1. KIT
I had a few problems with the schematic it came with but after a few googles got it working, then after I heard it running I chanced the whole thing and re-did the schematic, did away with the 6N9P and replace with 12ax7 and changed the whole setup and sound wow 100% the punch now from bass is that "punch" and excellent high end as well. just a thought this was the schematic that came with the kit. sound ok but again what a total difference replacing the preamp side for 12ax7.
 

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Thanks for the replies so far.

I've spent some time looking at photos on the web and at the schematic (which is below) and I reckon I understand most of it. I'm not happy with the mains fuse housing so I'll buy a better one at Maplin. I'm still not clear on the input/output and volume board connections but I'm more confident that I can work those out now.

Keep the info coming.

P
 

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Chinese amps with their 220V or 230V primary mains transformers are notorious for over running HT and LT supplies on 240V UK mains . You may find close to or above 7V on the heaters where it should be 6.3V and the same for the 5V rectifier winding . Watch out for capacitor ratings , I once had a Chinese amp made by Dared for repair which was poor engineering at it's utmost worst . This used hot melt glue to fix components to the chassis (which ran very hot in operation when the fuse didn't blow) also over run the reservoir capacitor as well as the heaters . This had a 220V primary mains transformer and the fix was to add series resistance to the HT rail and a common mode choke to the heater supply with an NTC thermistor in series with the mains transformer

316a
 
Hi all - thanks for the useful replies. I only got one 10k resistor so I assume I just need to cable the jump from the valve to the board.

What I can't work out is the connections from the input board - the output board and the volume control board. If anyone can supply me with a photo (Celcius?) I'd really appreciate it.
 
Thanks for the info on hot running stuff - a bit over my head at this point so I'm just plugging on with what I have.

Can someone help me with the transformer wires? I'm not completely sure if the 315v supply comes out of the top in this picture (i.e. on the same side as the mains input) or on the bottom side closest to the board.
 

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Thanks for the info on hot running stuff - a bit over my head at this point so I'm just plugging on with what I have.

Can someone help me with the transformer wires? I'm not completely sure if the 315v supply comes out of the top in this picture (i.e. on the same side as the mains input) or on the bottom side closest to the board.

From the photo i see 315V "should" come from the top since it is twisted with the ground black. But since I don't own the amplifier, just check the voltages (easy 5V or 315V...)

Check the photo here:
http://www.china-hifi-audio.com/images/boyuu-audio-amplifier/Boyuu-A9-EL34-tube-amp-3.jpg
 

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This is my rebuild after I was disappointed with the sound these kits give out

I disagree, these Chinese kits sound very well self alone and use very good components, but, as I did too, we can adjust the design for our personal taste.

For example you and me got the same Chinese amp (more or less) but we have choosen two completely different modifications:

1) you put negative global feedback, for which I dislike the sound (I have tested) and leave it without.

2) I put cathode bypass capacitor in the driver stage: again I skip the intrinsic local feedback, while you leave un-bypassed.

3) I put a switch to move to triode mode, and, again, you stay with the screen feedback of the ultra linear operation.

So for me Zero-feedback works the best, for you it seems that you like to have feedback: just personal taste, but not bad Chinese construction.

I maintained the triodes in parallel to lower the noise, since this is the main issue of these amplifiers

We both increased the bias of the final tubes, but you increased too hot I think. Are you sure that the stock output transformer doesn't saturate with so much DC? Also 24W is too much against the max dissipation of 25W: do you know that the loudspeaker load is an ellipse and not a straight line?

If you move from EL34 to KT66 you will get an additional improve.

Check my modifications:
http://www.diyaudio.com/forums/tube...be-amplifier-5z4p-rectifier-review-mod-2.html
 
All I'm saying is once I replaced the 6N9P and readjusted the schematic to take 12ax7 I would never go back to the Chinese 6N9P but the EL34B are very good the OPT are not so good but the main power Transformer is good, the Tube sockets are cheap and not so good the chassis are dangerous and no room to get in there, components are low grade which I replaced with better ones. But for what you pay for these kits it is worth rebuilding them to a higher standards. But at the end of the day it comes down to choice and sound that you are comfortable and what sounds right to your ears, for me I like the punch in the preamp of the 12ax7 gain has. :)