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Boyuu EL34 A9 Tube Amp
Boyuu EL34 A9 Tube Amp
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Old 6th August 2020, 01:34 AM   #1201
vinylkid58 is offline vinylkid58  Canada
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Quote:
Originally Posted by Tubby23 View Post
All else being the same, can I just install any el34 and not worry about changing the cathode resistor?
Probably. How many watts is the tube dissipating?

jeff
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Old 6th August 2020, 01:50 AM   #1202
Tubby23 is offline Tubby23  United Kingdom
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Originally Posted by vinylkid58 View Post
Probably. How many watts is the tube dissipating?

jeff
My power stage is currently stock apart from changing out the bypass caps for 470uf/63v.
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Old 6th August 2020, 01:55 AM   #1203
vinylkid58 is offline vinylkid58  Canada
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Well that wasn't what I was asking. What's the voltage at the EL34 cathode?

jeff
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Old 6th August 2020, 10:53 AM   #1204
daniellu is offline daniellu  Australia
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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.
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Old 6th August 2020, 01:30 PM   #1205
Tubby23 is offline Tubby23  United Kingdom
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Originally Posted by vinylkid58 View Post
Well that wasn't what I was asking. What's the voltage at the EL34 cathode?

jeff
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
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Old 6th August 2020, 01:53 PM   #1206
learn is offline learn  France
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The input impedance and 3.5K if I do not say stupidity. I saw it on page 15 post # 143. Having said that, danielu's advice is certainly the best.
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Old 6th August 2020, 02:07 PM   #1207
Tubby23 is offline Tubby23  United Kingdom
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Originally Posted by daniellu View Post
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.
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.
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Old 6th August 2020, 03:01 PM   #1208
learn is offline learn  France
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Default 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.
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Old 6th August 2020, 03:19 PM   #1209
Tubby23 is offline Tubby23  United Kingdom
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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.
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Old 6th August 2020, 08:24 PM   #1210
Tubby23 is offline Tubby23  United Kingdom
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Originally Posted by learn View Post
The input impedance and 3.5K if I do not say stupidity. I saw it on page 15 post # 143. Having said that, danielu's advice is certainly the best.
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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Last edited by Tubby23; 6th August 2020 at 08:54 PM.
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