• 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

anyway, if you spend your pentode in triode you decrease your gain, so the question does not arise.
moreover, it is recognized that the EF86 gives the best in triode, so the E80F will be even better in this mode.
I started to have the tour of the tests and for now, it is still the kt66 that gives the best result at home.
I tried 6p3,6p6s-e, kt77, el34,6l6gc, 6l6wgb.
I still have 6CA7 to try but I'm happy like that and I do not want to look further
 
@ Nitrate,
I don't think it made much differences. overall I am quite happy with the baseline noise of my A9. I tried my solid state Amp, without signal , I could hear the faint noise within 5cm from the mid range speakers. The A9, if i listened carefully, i could hear faint noise within 10cm. Practically it will never bother me.
Good weekend!
 
Administrator
Joined 2004
Paid Member
Hi huggygood,
I have to admit to preferring the 6CA7 over the EL34. Of course they are often mismarked. If its fat, it is a 6CA7 and not an EL34 (tall and skinny). The real 6CA7 is a beam power tube whereas the EL34 is a real pentode.

The KT66 is very close to a 7581A. That is a 6L6GC with 35 watt plate, and it does have the same plate characteristics as the 6L6GC from what I can tell.

-Chris
 
Hmmm,

I wired my remaining stock channel to introduce a little feedback and bypassed the 6n9p cathode to increase gain to compensate for the loss of overall gain. Listening tests swaping from one channel to the other showed no noticable difference between the two ( if you read my earlier posts i heavily modified one of my channels ). The feedback was done by inserting a 100r resistor between the bypassing of the 6n9p and ground. There i injected the feedback via 2k from the speaker terminal. I also increased current on fhe driver to better bias the tube ( 1k cathode resistor ), and also added 1k to the el34 cathode making a total of 333r cathode.

Now i have a difficult decision on what scheme to keep on both channels. My latest attempt has better hf responce, better squares but higher 2nd harmonics and higher output impedance. It now requires 2500mv to drive into clipping compared with 500mv on my other channel. It does however retain the spirit of this amplifier and does not invert the output waveform.

What would you do?
Both sound equal even if my scope says different.
 
I too prefer 6CA7 to EL34. in the case of my A9, it is the EL34 which gives the least good result but it is the Electron Tubes sold with the kit so it is not representative. 6p3S-e and 6L6gc are very close in sound signature 6P3s is close to the EL34, flat and bland, I want to say gray and dull. KT66 is shining, goes down well in the low end, clean, and looks easy. my 6ca7 are already used with my clone Leak and I do not want to touch it, however I will try KT88 and maybe even kt150 with a separate power supply for heating.

what I can say more is that in any case, this little amp is inferior to my harman A300 a little modified, the Harman is a little more "noisy" but remains a real pleasure every day.

end of the story for this little Chinese beetle, I put it on sale. for who wants to have fun, it's a good amp but for the price, it is still better to find a TRUE amp with a TRUE scheme and a TRUE brand on the second hand market. I think the limiting factor is always the opt and you can not turn a donkey into a racehorse. yesterday, to "see" I confronted him with a 1030 marantz, the boyuu was ridiculous next to the marantz, I made my decision.

one last thing. do not use the power cable supplied with the kit there is a real danger to use it, it is not a 3x0.75 but rather a 3x0.25 with insulators of very poor quality that mimic the silicon but melt near the soldering iron.
 
Did someone also figured out that with the standard main switch at the front the left channel has 50 Hz hum. I put the twistet wire and the main switch out of the chassis and the 50Hz hum disappear. Just a small amount of 100Hz hum from the rectifier is still there, but I have the standard filter capacitor in place. Will be increased soon.

Does the GD24491 RMS1035 Lorlin decrese noise introduced in the left channel preamp?
 
I bought one of these amps earlier in the year but didn't build it myself as at the time I didn't feel confident enough to tackle it just from a schematic. The chap that built it did a pretty good job but I have a fair bit of mains hum. I have tried 3 different rectifier valves but not really much difference. Will modding it too "V2 schematic" as above cure all my hum issues? The only bit I don't have is a 10H choke (mine is 3H). I also note the the V2 schematic is marked 240v and mine is 220V (I'm in the UK). I am getting 245-250v out of the socket so I'd imagine the HT and heater voltages are going to be on the high side. C301 gets quite warm and so does C303, should I change these to higher voltage rates caps? they are 33uF 400v currently and C302 is a 220uF 450v (my original schematic says 22Uf and 150uF here so obviously manufacturer has already upped the values a bit.
Hum is consistent and does not alter with adjustment of the volume control, it goes away for a few seconds if I switch the mains off with the amp playing while the caps drain.
 
You need two 100 ohm / 2 W resistors, one from each heater side to ground. That removed the hum on mine (I used 1k / 0.6 W resistors since I had nothing better at hand).

Just added two 1 watt 100 ohm resistors between heater supply and ground. That has removed 80% of the hum.

What does the C204,C205,C104 and C105 mod do? and the R107 and R207 resistors (I have 2 off 1K here) but Rev2 schematic shows one 500 ohm 6W here instead.

The chap that built it hadn't grounded the 0V speaker terminals of the output transformers, Is there any benefit to this? I have no connected them to ground. Metal chassis isn't grounded either.
 
Hello everyone, I have wanted to make a tube amplifier for a long time. After browsing all the pages about: "BOYUU A9", I decided to dream from reality.
Here is what I have already assembled and soldered.
I'm sorry for my english (Google Translation).:wave:
 

Attachments

  • Part 1 (2).jpg
    Part 1 (2).jpg
    631.1 KB · Views: 403