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#1 |
diyAudio Member
Join Date: Nov 2005
Location: Québec
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Take a look at this amp : http://www.geocities.com/mydesign_99/PP6L6.JPG
- Does it realy going to draw 200 mA over the power transformer ? Cause I would like to use a edcor transformer for 2 channels of this amp... and I think a 500 mA is a biiiit overpower. |
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#2 |
diyAudio Member
Join Date: Jan 2002
Location: nowhere
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Yes.
Since the diff stage already has a negative supply for its ccs bias, why not use the same supply for the 6L6 bias and not use R11 and C3? |
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#3 |
diyAudio Member
Join Date: Jan 2006
Location: SAO PAULO - SP
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Hi quitvinny ,
Except for the input stage , the output schematic PP 6L6 Class A is a classic , and it REALLY DRAWS about 170 - 200 mA at the full power . and for two channels , you will really need about 400 - 450 mA of useful current . The total output power is 18 Wats of pure Class A per channel . But the sound is very amazing , very smooth and I'm sure that you will like it . Regards Carlos |
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#4 |
diyAudio Member
Join Date: Nov 2005
Location: Québec
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Ok, I`ll check with edcor if 1x450 mA or 2x250 mA is less costy. For the output tranny, who can I calculate the primary impedance ? Is 7600 ohms will be allright like the CXPP25-8-7.6K ?
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#5 |
diyAudio Member
Join Date: Nov 2005
Location: Québec
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For the output tranny, I check on http://tdsl.duncanamps.com/show.php?des=6L6
Zout is the impedance right ? do I look in the good column : Class : A PP Va : 270 .....Zout 5000 ?? |
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#6 |
diyAudio Member
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Can I use a 6sn7 in the place of 12AT7?
What is the sound of this amp? |
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#7 |
diyAudio Member
Join Date: Jan 2006
Location: SAO PAULO - SP
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Hi quitvinny ,
As I said , this 6L6 PP Class A schematic is a classic and the correct Zout , that is the total load ( plate to plate ) is 5000 ohms , and the +B correct value is 270 – 300 Volts . Use a output tranny that can “hand” 25 Watts or more . Preferably use a matched pair or a same brand / same lot pair of 6L6’s in each channel , because the quiescent current is high ( about 170 mA total or aprox. 85 mA per tube ) and if the current through one tube is very diferent from the current through another tube , this fact will cause a lot of distortion at the output. ( don’t forget : the output tubes are cathode coupled by the 125 ohms resistor ) Don’t try to change the cathode resistor , the correct value is on the schematic ( 125 ohms ) , and this value will give an aprox. grid bias value of ( - ) 20 Volts . Don’t worry about the high value of quiescent current , because the tubes are connected in the push-pull way , and the magnetic field created by one tube is entirely canceled by the opposite magnetic field created by another tube . The circuit is highly stable , and you won’t have any kind of trouble . Good luck , Carlos |
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#8 |
diyAudio Member
Join Date: Jan 2006
Location: SAO PAULO - SP
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Hi mod_evil
No you can’t use the 6SN7 in the place of 12AT7 in anyway , they are totally different . The 6SN7 is a medium mu and the 12AT7 is a high mu dual triode . The 6SN7 Class A grid bias is ( - ) 8 Volts and the 12AT7 Class A grid bias is ( - ) 2 Volts at 250 Volts plate voltage , the plate resistance and transconductan- ce are different too . If you follow the above gave schematics , will result a very amazing and a very smooth sound . Carlos |
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#9 |
diyAudio Moderator Emeritus
Join Date: Jan 2004
Location: Jakarta
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The reason the 12AT7 was chosen for the first stage, I suspect, was that it can draw enough current to drive the LM317 and also has reasonably high gain. A 12AX7 has more gain but would draw too little current. 12AU7 (or 6SN7) would be the opposite.
If I were you, I would not use the LM317 as a CCS - it's reputed to have a poor high frequency response. Choose a better CCS, maybe using a couple of transistors of appropriate type. If you do that, it would also allow you to use a higher gain but lower current tube for the first stage, such as a 12AX7 or, better still for sound quality, a 6SL7. If you want to make it sound even nicer, use a choke in place of the 100 ohm resistor (R12) in the power supply, especially if you're planning a common supply for both channels. |
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#10 |
diyAudio Member
Join Date: Nov 2005
Location: Québec
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Hey, thank you all,
For CCS, where can I find good desing information ? or if you have shematic lying around send it to me. And if I do that, can ou tell me ray_moth what I will have to change to use 6SL7 ? Last question : I saw silver-steel bar on ebay (dia : 1 mm) does anyone have ever work with this material ? I would like to use it as a bus bar. |
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