6SN7 CCS

Cassiel · 9th February 2006, 09:02 PM

Hi,

I'm trying to build a SE 6as7 but i'm having some problems. Main reason is the driver tube- a 6sn7. OK the output stage is solved, i am running the 6as7 with 250 volts at the plate(maximum allowed according to data sheet) and low current and i am getting a lot of power (good) but i need a good sounding driver stage...
I tried direct coupling , SRPP and 12at7 to 6sn7....i didn't like any of them

As i said before the driver is a 6sn7...why? Because i like them and got them cheap. The 6sn7 needs lots of volts hence my 330V B+. Yes i know, too high for the 6as7 but i also got them cheap.

Then i found this schematic...
http://www.jogis-roehrenbude.de/Lese...7/Endstufe.gif

I've never tried a CSS but it seems to me a great idea for this amp. I am not paralleling the 6as7's (don't need many watts) but i want to copy the driver stage. I have bought all the parts for the ccs but now i am in doubt:

- does it have to be same B+ or it could be 20 volts more or less.

-the LED and the diode in the schema...can i use any diode, any LED?

Any other advice about ccs's welcomed... i know very little.

SY · 9th February 2006, 09:09 PM

The LEDs can be anything, but you have to know their forward voltage to properly calculate the emitter resistor. There are whole masses of posts here about just that subject- a few minutes searching ought to turn up all the formulas and schematics you could ever want.

Cassiel · 9th February 2006, 09:46 PM

Quote:

a few minutes searching ought to turn up all the formulas and schematics you could ever want.

Umm i really dont want any but ooook i'll do some homework tonight.

Progress so far. Wine box.

Cassiel · 10th February 2006, 02:46 PM

It doesn't work. 0 volts at the 6sn7 cathode. No music, nothing,nada.
CCS= 310 VOLTS IN, 307 VOLTS OUT.

LED's light up. What could be wrong? If i had miswired a transistor would i get 307 volts at the plate?

Any ideas for troubleshooting the circuit?

SY · 10th February 2006, 02:53 PM

Clearly, there's no current being drawn. Disconnect the CS from the tube and verify its operation- from the CS to ground, connect a 20K resistor. Is there 200V across it? If so, the CS is working.

Most likely, you've got a wiring error.

Cassiel · 10th February 2006, 03:09 PM

Thanks SY, i get 232 volts with a 22k resistor to ground.

Is it working?

Cassiel · 10th February 2006, 03:13 PM

It works ....10v at the 6sn7 cathode.

Thanks again SY.

kevinkr · 10th February 2006, 04:07 PM

What operating point have you chosen for the 6SN7?
Cathode resistor value?

Kevin

SY · 10th February 2006, 04:10 PM

His schematic is linked in the first post. 10mA, 1k cathode resistor.

I wouldn't go that route, but it's not my design.

kevinkr · 10th February 2006, 04:35 PM

Hi Sy,
What do you think of the operating point chosen? I suspect that there is very little voltage headroom to spare here..

Imho this seems like a good place to try transformer coupling if he was so inclined...

9th February 2006, 09:02 PM	#1
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	6sn7 Ccs Hi, I'm trying to build a SE 6as7 but i'm having some problems. Main reason is the driver tube- a 6sn7. OK the output stage is solved, i am running the 6as7 with 250 volts at the plate(maximum allowed according to data sheet) and low current and i am getting a lot of power (good) but i need a good sounding driver stage... I tried direct coupling , SRPP and 12at7 to 6sn7....i didn't like any of them As i said before the driver is a 6sn7...why? Because i like them and got them cheap. The 6sn7 needs lots of volts hence my 330V B+. Yes i know, too high for the 6as7 but i also got them cheap. Then i found this schematic... http://www.jogis-roehrenbude.de/Lese...7/Endstufe.gif I've never tried a CSS but it seems to me a great idea for this amp. I am not paralleling the 6as7's (don't need many watts) but i want to copy the driver stage. I have bought all the parts for the ccs but now i am in doubt: - does it have to be same B+ or it could be 20 volts more or less. -the LED and the diode in the schema...can i use any diode, any LED? Any other advice about ccs's welcomed... i know very little.

9th February 2006, 09:09 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	The LEDs can be anything, but you have to know their forward voltage to properly calculate the emitter resistor. There are whole masses of posts here about just that subject- a few minutes searching ought to turn up all the formulas and schematics you could ever want. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

10th February 2006, 02:53 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Clearly, there's no current being drawn. Disconnect the CS from the tube and verify its operation- from the CS to ground, connect a 20K resistor. Is there 200V across it? If so, the CS is working. Most likely, you've got a wiring error. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

10th February 2006, 04:07 PM	#8
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	What operating point have you chosen for the 6SN7? Cathode resistor value? Kevin __________________ www.kta-hifi.net

10th February 2006, 04:10 PM	#9
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	His schematic is linked in the first post. 10mA, 1k cathode resistor. I wouldn't go that route, but it's not my design. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

10th February 2006, 02:46 PM	#4
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	It doesn't work. 0 volts at the 6sn7 cathode. No music, nothing,nada. CCS= 310 VOLTS IN, 307 VOLTS OUT. LED's light up. What could be wrong? If i had miswired a transistor would i get 307 volts at the plate? Any ideas for troubleshooting the circuit?

10th February 2006, 03:09 PM	#6
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	Thanks SY, i get 232 volts with a 22k resistor to ground. Is it working?

10th February 2006, 03:13 PM	#7
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	It works ....10v at the 6sn7 cathode. Thanks again SY.

10th February 2006, 04:35 PM	#10
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Hi Sy, What do you think of the operating point chosen? I suspect that there is very little voltage headroom to spare here.. Imho this seems like a good place to try transformer coupling if he was so inclined... __________________ www.kta-hifi.net

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