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Boyuu EL34 A9 Tube Amp
Boyuu EL34 A9 Tube Amp
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Old 18th April 2015, 11:52 PM   #111
Gidu is offline Gidu  France
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Join Date: Aug 2007
Location: FRANCE
Hi!

I changed the filter capacitor ( 150 microfarads to 330 microfarads - 450 Volts ) and I added two 100 Ohm resistors to balance the heating line of 6N9PJ tubes connected to the chassis ground.

Finally, I added a grid resistor of 3.3 kilo ohm on 6N9PJ tubes.

The buzz has totally disappeared, only a very slight hum subiste heard only if the ear is glued to the speakers ... It's almost perfect !

Here are pictures of the mods :

Click the image to open in full size.
Nouveau condensateur de filtrage : 33 microfarads 450 Volts

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Résistances d'équilibrage du 6,3 Volts de chauffage des filaments des 6N9PJ (2 x 200 Ohms en //)

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Résistance de grille de 3300 Ohms et connection des deux résistances d'équilibrage sur le 6,3 Volts

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2ème résistance de grille de 3300 Ohms et connection des deux résistances d'équilibrage sur le 6,3 Volts

That's all for today !

Gidu

Last edited by Gidu; 18th April 2015 at 11:55 PM.
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Old 19th April 2015, 12:36 AM   #112
jeffhigh is offline jeffhigh  Australia
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Have you removed the B3 connection to the 6n9p filaments?
You don't want to be using both heater elevation and artificial centre tap to ground.
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Old 19th April 2015, 06:28 AM   #113
Gidu is offline Gidu  France
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Well, i don't have any connection between B3 and the 6N9P filaments (your schematic is different from mine) ... I only have now artificial center tap to ground !

Gidu

Last edited by Gidu; 19th April 2015 at 06:55 AM.
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Old 19th April 2015, 07:33 AM   #114
Gidu is offline Gidu  France
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Join Date: Aug 2007
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Here is the simple schematic of this mod (this is just an example) :

Click the image to open in full size.

The resistors can be replaced by a wound potentiometer 100 Ohms / 3 Watts , allowing fine-tune balancing of 6.3 Volts.

(The current through the resistors is: I = 6.3 / 100 = 0.063 mA , so the power dissipated is: P = 0,063 x 63 = 0.396 Watts or P = 6,3 x 6,3 / 100 = 0,396 Watts)

PS : Warning to the mount of the new 300 microfarads capacitor : its diameter is 30 mm , so mounting is not possible if you use the spacers provided with the kit to secure the PCB ! See specifications of this capacitor here : http://www.conrad.fr/ce/fr/product/1...HOP_AREA_17428

Gidu

Last edited by Gidu; 19th April 2015 at 07:54 AM.
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Old 19th April 2015, 08:17 AM   #115
jeffhigh is offline jeffhigh  Australia
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Sorry, assumed your kit was the same as the first schematic posted on this thread which has a B3 supply elevating the heater
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Old 20th April 2015, 04:56 PM   #116
Gidu is offline Gidu  France
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Sorry for the mistake : you have to read 0,068 A or 68 mA instead of 0,068 mA ...

Gidu
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Old 22nd April 2015, 08:25 PM   #117
Gidu is offline Gidu  France
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Join Date: Aug 2007
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I received and installed my new tubes : EL34 EH , 5U4GB EH and 6SN7 EH.
I have no buzz and A09 works perfectly!
It remains for me to have the patience to let these tubes lapped slowly ... but for now , the sound is already very satisfying !

Gidu
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Old 23rd April 2015, 08:04 AM   #118
DirkLeh is offline DirkLeh  Australia
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Hi Gidu,
Just wondering....
Wasn't the replacement for the 6N9P actually the 6SL7 as opposed to the 6SN7?
The two have entirely different characteristics (amplification, resistance)!
Strange that they apparently work for your configuration on the A9 kit, or did you make further changes?
I will give this resistor mod of yours on the heating supply a chance and see if that makes a difference for mine.
Will report.
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Old 23rd April 2015, 11:15 PM   #119
Gidu is offline Gidu  France
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Join Date: Aug 2007
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Hi DirkLeh !

yes, you're right : i made a mistake, the exact equivalent for the 6N9P is effectively the 6SL7. So i did take off the 6SN7 to replace it by the 6N9P ...

Gidu
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Old 25th April 2015, 10:18 AM   #120
Gidu is offline Gidu  France
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Join Date: Aug 2007
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... But it worked perfectly, I still even replaced the 6N9P because, after verification, the value of the 6SN7 heating current is twice the 6N9P (600 mA instead of 300 mA), which for two tubes carries the filament heating current to 1.2 Ampères while the maximum current debited by winding heating 6N9P supply transformer is 1 A !

Gidu
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