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/Leserbriefe/Heiko-6AS7/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.
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/Leserbriefe/Heiko-6AS7/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.
Kevin and Shifty: i'm really open to ideas. I need a driver stage with 6sn7's, that's all.
I've tried driver stages for 300b's. Angela 300b driver stage sucks with the 6as7 IMHO. Great detail but thin sound. Audio note srpp ....not my taste.
So far best sound was with an ef184/6ej7 triode connected to a 6sn7 grounded cathode stage.
I have a preamp. I might try a 6sn7 grounded cathode stage to a 6sn7 cathode follower.
About the schematic i posted: css didn't work. Voltages are ok but when is time for the music...oh my! Volume up and down, scratches, weird noises...etc. Voltages do not oscillate. Everything is allright, only i could have mistaken the emitter for the collector but i doubt it. Emitter is the one with the arrow pointing to the transistor right?
I've tried driver stages for 300b's. Angela 300b driver stage sucks with the 6as7 IMHO. Great detail but thin sound. Audio note srpp ....not my taste.
So far best sound was with an ef184/6ej7 triode connected to a 6sn7 grounded cathode stage.
I have a preamp. I might try a 6sn7 grounded cathode stage to a 6sn7 cathode follower.
About the schematic i posted: css didn't work. Voltages are ok but when is time for the music...oh my! Volume up and down, scratches, weird noises...etc. Voltages do not oscillate. Everything is allright, only i could have mistaken the emitter for the collector but i doubt it. Emitter is the one with the arrow pointing to the transistor right?
kevinkr said:
Well, if there really is 10mA flowing, the plate to rail voltage would be pretty skinny; I'd guess about 250-260V on the 6SN7 plate. You're also driving into a low mu tube with moderately high capacitance. Yeah, a transformer would help.
What I also see as a potential problem with this circuit is the high 2nd harmonic you'll get from the combination of the plate CCS and the unbypassed cathode resistors. Now, it is possible that the designer was being fiendishly clever and using this to counteract the 2nd in the output stage, but if we look at that first stage in isolation, I'd expect pretty high distortion at the required swing.
CCS nightmare
Now this is getting funny. I did recheck and tried again the ccs and i don't know what i have built but i know it's weird. It kills some musicians and keep others...i only heard the drummer in the last song... sometimes voices come in and then disappear... all with some scratchs now and then as if a crazy dj had remixed all my cd's.
One thing i have noticed: the 150k resistor to ground(1 watt) gets too hot, i am going to change it to 2 watts, is this normal?
Now this is getting funny. I did recheck and tried again the ccs and i don't know what i have built but i know it's weird. It kills some musicians and keep others...i only heard the drummer in the last song... sometimes voices come in and then disappear... all with some scratchs now and then as if a crazy dj had remixed all my cd's.
One thing i have noticed: the 150k resistor to ground(1 watt) gets too hot, i am going to change it to 2 watts, is this normal?
Hi Jeapel,
your ccs looks just like mine except for those 2 diodes (1n4004, 1n4148), guess they are there to make the circuit safer. My ccs works, there is a constant current but when AC comes to play i hear a lot of problems....with a plate resistor the circuit works fine.
It must be a transistor...maybe faulty.
I looked at your driver stage. I could do it but any reasons to do so? I will need another power supply or is the 6as7 cathode dropping 150volts?
I have several options, being a cathode follower the best one at the moment.
Thanks for your answer...yes 2 watts.
your ccs looks just like mine except for those 2 diodes (1n4004, 1n4148), guess they are there to make the circuit safer. My ccs works, there is a constant current but when AC comes to play i hear a lot of problems....with a plate resistor the circuit works fine.
It must be a transistor...maybe faulty.
I looked at your driver stage. I could do it but any reasons to do so? I will need another power supply or is the 6as7 cathode dropping 150volts?
I have several options, being a cathode follower the best one at the moment.
Thanks for your answer...yes 2 watts.
attention here 
-jogis use led(light diode) for diode and voltage drop is 1.7v
ccs= (1.7 - .7)/100=10ma
-in my case i replace led by 3 x 1n4004 and voltage drop is
3 x .7=2.1 ccs=(2.1- .7)/240=5 to 6 ma
-1n4148 is for transistor protection
-jogis use 10ma for 2 x 6sn7 5ma for each tube
-normal bias for 6sn7 is around 2 to 5 ma 10ma is limit
-don t forget for any tube to my opinion ??
for driver stage must be around 25 to 30 % of pa max. (in watt)
for output stage must be around 60 % of pa max.
it s for best tube life check volt across tube X current tube = watt
pa max. is plate dissipation maximum
6as7 is 13 watt max. if i remenber well
-jogis use led(light diode) for diode and voltage drop is 1.7v
ccs= (1.7 - .7)/100=10ma
-in my case i replace led by 3 x 1n4004 and voltage drop is
3 x .7=2.1 ccs=(2.1- .7)/240=5 to 6 ma
-1n4148 is for transistor protection
-jogis use 10ma for 2 x 6sn7 5ma for each tube
-normal bias for 6sn7 is around 2 to 5 ma 10ma is limit
-don t forget for any tube to my opinion ??
for driver stage must be around 25 to 30 % of pa max. (in watt)
for output stage must be around 60 % of pa max.
it s for best tube life check volt across tube X current tube = watt
pa max. is plate dissipation maximum
6as7 is 13 watt max. if i remenber well
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