6L6 Push pull -- Power tranny question

guitvinny · 15th May 2006, 04:54 PM

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.

SemperFi · 15th May 2006, 06:49 PM

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?

refference · 15th May 2006, 10:56 PM

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

guitvinny · 16th May 2006, 01:08 PM

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 ?

guitvinny · 16th May 2006, 01:40 PM

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 ??

mod_evil · 16th May 2006, 02:22 PM

Can I use a 6sn7 in the place of 12AT7?

What is the sound of this amp?

refference · 17th May 2006, 01:19 AM

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

refference · 17th May 2006, 01:37 AM

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

ray_moth · 17th May 2006, 05:15 AM

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.

guitvinny · 17th May 2006, 02:06 PM

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.

15th May 2006, 04:54 PM	#1
guitvinny diyAudio Member Join Date: Nov 2005 Location: Québec	6L6 Push pull -- Power tranny question 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.

16th May 2006, 02:22 PM	#6
mod_evil diyAudio Member Join Date: Dec 2004 Location: Rio	Can I use a 6sn7 in the place of 12AT7? What is the sound of this amp? __________________ My blog! www.felipenavarro.net

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Push-Pull question	roomi	Power Supplies	5	26th December 2008 10:53 PM
push pull power amp design question (a lot of actually :) )	krusty75	Tubes / Valves	6	25th September 2008 05:07 PM
modify parallel push-pull EL84 to single push-pull	chungtat	Tubes / Valves	12	3rd November 2005 11:25 PM
Double push-pull versus single push-pull	jraraujo	Tubes / Valves	19	19th October 2002 12:23 AM
Power rating for push pull configuration question	miked15	Tubes / Valves	4	15th May 2002 02:50 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

15th May 2006, 06:49 PM	#2
SemperFi diyAudio Member Join Date: Jan 2002 Location: nowhere	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?

15th May 2006, 10:56 PM	#3
refference diyAudio Member Join Date: Jan 2006 Location: SAO PAULO - SP	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

16th May 2006, 01:08 PM	#4
guitvinny diyAudio Member Join Date: Nov 2005 Location: Québec	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 ?

16th May 2006, 01:40 PM	#5
guitvinny diyAudio Member Join Date: Nov 2005 Location: Québec	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 ??

17th May 2006, 01:19 AM	#7
refference diyAudio Member Join Date: Jan 2006 Location: SAO PAULO - SP	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

17th May 2006, 01:37 AM	#8
refference diyAudio Member Join Date: Jan 2006 Location: SAO PAULO - SP	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

17th May 2006, 05:15 AM	#9
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	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.

17th May 2006, 02:06 PM	#10
guitvinny diyAudio Member Join Date: Nov 2005 Location: Québec	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.