My power stage is currently stock apart from changing out the bypass caps for 470uf/63v.
The stock transformer was rated 200w, I had no trouble to make it work with KT88 tubes for long time listening, I think it's waste of time and money to 'upgrade' to different OPT, the stock ones are good enough. A few other small mods will give you significant improvement/changes in this amp, as mentioned Tung-Sol tubes, I like them, and Mullard reissues, they are better than my other overpriced PSVANE tubes, PSVANE just matched better than stock Shuguang tubes. I would definitely increase the coupling capacitors, this makes bass better and the amp seems to increase the total output power too, it doesn't put any stress on power supply. Also, an anode follower feedback changes the colour of the sound too, in the better way.
Here are all my readings:
Power Rail
B+. 339v
B2. 319v
Volt Divider. 45.6v
Left Channel
EL34 cathode. 22v
OPT Brown. 325v
OPT Screen Tap (Blue). 330v
6N9S Cathode 2.21v
Right Channel
EL34 cathode. 22.6v
OPT Brown. 327v
OPT Screen Tap (Blue). 330v
6N9S Cathode 2.3v
I ordered these
EL34-SVETLANA WINGED C
Despite having bought both .47uF and .22uf coupling caps, I chickened out at the last minute and installed the .22s. I was concerned that the OPTs wouldn't have the guts for .47s.. and something about too much phase rotation...?
As things stand I definitely have bass but it's not as punchy as my old SS stereo. Mind, I'm using a pair of old Mordant Short ms 3.10s bookshelf type speakers I got off a car boot sale.
Because I added caps to the driver stage, I also added local feedback. A wire runs from the coupling cap's outputs back to the 6N9S' grid via a 1mR resistor.
Be patient my friend 
For optimum sound, the vacuum tubes must have been in operation for a certain number of hours. The sound will gain in quality.
After that you can consider modifying things in your amp.
In any case the bass will be better but you have to make your "Boyyu" work. during sometime.
For optimum sound, the vacuum tubes must have been in operation for a certain number of hours. The sound will gain in quality.
After that you can consider modifying things in your amp.
In any case the bass will be better but you have to make your "Boyyu" work. during sometime.
I'm just like that....I never gave the original design a chance! LOL
I have been listening to it for several hours these last couple of days and have been tweaking my listening/Living room. Something that has brought on a performance increase is my removing the little tube preamp/buffer that stood between the DAC and the A9. Bass and attack are much better.
I have been listening to it for several hours these last couple of days and have been tweaking my listening/Living room. Something that has brought on a performance increase is my removing the little tube preamp/buffer that stood between the DAC and the A9. Bass and attack are much better.
I just read that, because of my local negative feedback existing, my coupling caps are high enough, in fact should be lower at .159uf because they form a high pass filter with the 1megR resistors and the cutoff should be at 1hz.
Mine, at .22uf together with the 1megR resistor cut off at 0.7hz.
Still, 70% of 1hz is apparently ok. I was lucky.
It has the advantage that my coupling caps are very low reactive towards all audio frequencies, even the low ones.
Had I installed .47uf as I might have then the cutoff would have been much too low.
The Valve Wizard
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Hi all,
Sorry I haven't posted in the last few months. But I've been reading the posts in this forum and enjoying the sound of my A9.
After learning a lot about tube amps in this forum, I think I'm ready to build a more complex and powerful tube amp. So can somebody recommend a good Class AB tube amp kit for me to buy?
Thanks,
F Lima
Sorry I haven't posted in the last few months. But I've been reading the posts in this forum and enjoying the sound of my A9.
After learning a lot about tube amps in this forum, I think I'm ready to build a more complex and powerful tube amp. So can somebody recommend a good Class AB tube amp kit for me to buy?
Thanks,
F Lima
Hi Lima,
there isn't many push and pull kits available, I guess, you can try this one,
Vacuum Tube Push-Pull Amplifier Kit - Part 1 - YouTube
EL84 / 6P14 13W AB Class Electron Vacuum Tube Push-pull HIFI Poststage AMP Kits | eBay
Those kits become quite expensive, I would otherwise consider buy reasonable good PNP amp, I know it's a fun journey in building one myself.
there isn't many push and pull kits available, I guess, you can try this one,
Vacuum Tube Push-Pull Amplifier Kit - Part 1 - YouTube
EL84 / 6P14 13W AB Class Electron Vacuum Tube Push-pull HIFI Poststage AMP Kits | eBay
Those kits become quite expensive, I would otherwise consider buy reasonable good PNP amp, I know it's a fun journey in building one myself.
I believe that was the impedance of the new Japanese OPTs he got for his system.
The maker's website says that the turn ratio of the OPTs are "66-32".
Do they mean 66.32:1 ?
Or do they mean 66:1 for the 8 ohm tap and 32:1 for the 4 ohm tap?
I went through the same journey and have decided to build the Blueglow / Kegger KT88 as my first scratch build amp.
Mark at Blueglow has his build on YouTube and AudioKarma have a great forum thread on the development of the design.
I'm just waiting for the transformers to arrive from Edcor in the US and I can start putting it together.
Ok Gentlemen,
Let's talk Tube Dissipation! LOL
Have any of you changed the "standard" bias?
My system's EL34s, with with their 500R (actually 479.285...) cathode resistors and particular voltages are running with a plate current of 45.90mA or rather a plate dissipation of 56%.
According to a few sites Ive been reading cathode biased tubes can be safely run at 100% PD with better sound quality (livelier, less flat, etc).
I'm interested in running mine at 90%, once I upgrade my OPT's to 6.6K/15W.
So, anyone? And the results?
Let's talk Tube Dissipation! LOL
Have any of you changed the "standard" bias?
My system's EL34s, with with their 500R (actually 479.285...) cathode resistors and particular voltages are running with a plate current of 45.90mA or rather a plate dissipation of 56%.
According to a few sites Ive been reading cathode biased tubes can be safely run at 100% PD with better sound quality (livelier, less flat, etc).
I'm interested in running mine at 90%, once I upgrade my OPT's to 6.6K/15W.
So, anyone? And the results?
Here's a video of mine pumping out supertramp.
Even with the stock bias and OPTs, it plays quite loud before noticeable distortion sets in! I've now tube rolled Tung-Sol 6SL7GT and Svetlana Winged C. Bigger OPTs to come and re-biasing to match!
Speakers are Cambridge Audio SX-60.
Boyuu A9 - YouTube
Even with the stock bias and OPTs, it plays quite loud before noticeable distortion sets in! I've now tube rolled Tung-Sol 6SL7GT and Svetlana Winged C. Bigger OPTs to come and re-biasing to match!
Speakers are Cambridge Audio SX-60.
Boyuu A9 - YouTube
Tubby23,
56% at 45.90mA.
90% (90/56) x 45.90 = 73.77mA
There will be the following changes in your amplifier:
The B+ Voltage will drop because of the additional load current.
The Power transformer will get hotter.
The Self Bias Voltage will go down (because you have to use less resistance than the 479 Ohms you are using now,
in order to get more current).
The B+ draw now is over 90mA.
It will be going to more than 147.5 mA.
How warm, or how hot does your power transformer get at the 45.9 mA/tube now?
How about the rectifier tube. Check the tube specifications for the new current (probably OK), But be sure to check the rectifier's rating of the capacitance of the first filter cap that is in your amp, versus the higher current level the rectifier will be running at.
56% at 45.90mA.
90% (90/56) x 45.90 = 73.77mA
There will be the following changes in your amplifier:
The B+ Voltage will drop because of the additional load current.
The Power transformer will get hotter.
The Self Bias Voltage will go down (because you have to use less resistance than the 479 Ohms you are using now,
in order to get more current).
The B+ draw now is over 90mA.
It will be going to more than 147.5 mA.
How warm, or how hot does your power transformer get at the 45.9 mA/tube now?
How about the rectifier tube. Check the tube specifications for the new current (probably OK), But be sure to check the rectifier's rating of the capacitance of the first filter cap that is in your amp, versus the higher current level the rectifier will be running at.
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