The good news is that you've got all the parts in there and the amplifier should work.
The bad news is that the operating point for the 6SN7 in the schematic is in a fairly low current and non-linear area. It might sound OK, but I strongly suggest either:
going through the exercise of plotting load-lines to determine the circuit values as outlined in the articles I mentioned in my earlier reply
-or-
building tried and true designs
As to the 6SN7 being able to drive a 2A3, it should be no problem if you're talking about current when you say drive, especially if the 2 halves are paralleled. The issue is gain. A 6SN7 may or may not provide enough gain for a 2A3; it is completely dependent on the sources and preamps. Test discs and a multimeter can answer that question.
The bad news is that the operating point for the 6SN7 in the schematic is in a fairly low current and non-linear area. It might sound OK, but I strongly suggest either:
going through the exercise of plotting load-lines to determine the circuit values as outlined in the articles I mentioned in my earlier reply
-or-
building tried and true designs
As to the 6SN7 being able to drive a 2A3, it should be no problem if you're talking about current when you say drive, especially if the 2 halves are paralleled. The issue is gain. A 6SN7 may or may not provide enough gain for a 2A3; it is completely dependent on the sources and preamps. Test discs and a multimeter can answer that question.
Make C4 bigger?
Perhaps it could be 100uF at least so the bass won't poop out prematurely. Fifty years ago a cap this size would have been difficult and expensive so they just didn't use them. No excuse nowadays. Make sure the heat from the resistor leads doesn't travel up the cap leads and shorten the life of the cap.
GP.
Perhaps it could be 100uF at least so the bass won't poop out prematurely. Fifty years ago a cap this size would have been difficult and expensive so they just didn't use them. No excuse nowadays. Make sure the heat from the resistor leads doesn't travel up the cap leads and shorten the life of the cap.
GP.
jeff mai,
again you give very good advice, i agree with what you said above.
mig-ru,
have looked on the plate charactereistics of the 6SN7 and done some rough calculations.
At B+ of 300V, 100k for the load resistor is way too high, 10k should be ok. Tube runs at about 6.8 mA quiescent current then, at a bias of -8V; for that you may have to increase R3 to1.2k. I have ignored to consider voltage drop across P3 for guesstimating R7, i have assumed 300V.
You have to actually measure cathode current and you will have to adjust it by ear if ncecessary.
Voltage gain of the input stage will be 9.9 as judged from the plate characteristics. I remember i suggested an active load or a choke, with this you would have gain of 20 which is enough. With a resitive load at 2V rms, you need an additional stage or an 1:2 interstage transformator to deliver needed swing to the 2A3's grid.
again you give very good advice, i agree with what you said above.
mig-ru,
have looked on the plate charactereistics of the 6SN7 and done some rough calculations.
At B+ of 300V, 100k for the load resistor is way too high, 10k should be ok. Tube runs at about 6.8 mA quiescent current then, at a bias of -8V; for that you may have to increase R3 to1.2k. I have ignored to consider voltage drop across P3 for guesstimating R7, i have assumed 300V.
You have to actually measure cathode current and you will have to adjust it by ear if ncecessary.
Voltage gain of the input stage will be 9.9 as judged from the plate characteristics. I remember i suggested an active load or a choke, with this you would have gain of 20 which is enough. With a resitive load at 2V rms, you need an additional stage or an 1:2 interstage transformator to deliver needed swing to the 2A3's grid.
mig-ru,
i merge your 2A3 threads together, same topic, same project. Just wanted to let you know.
planet10's schematic of the Kismet amp made me think. A good calssic design after all, but i have got a prejudice against an ECC88 having to deliver full swing, this is a small signal tube. What you could choose: an E80CC or an ECC40, both are georgeous audio tubes which will do exactly what you need: µ=30, stage gain about 15 with resitive load and able to give the 2A3 a kick.
i merge your 2A3 threads together, same topic, same project. Just wanted to let you know.
planet10's schematic of the Kismet amp made me think. A good calssic design after all, but i have got a prejudice against an ECC88 having to deliver full swing, this is a small signal tube. What you could choose: an E80CC or an ECC40, both are georgeous audio tubes which will do exactly what you need: µ=30, stage gain about 15 with resitive load and able to give the 2A3 a kick.
2A3 SE AMP
Bernhard,
With all due respect ; the E80CC is by far one of the best choices here on paper but EXPENSIVE !
( I know you're sitting on a couple of hundreds of them,still...)
ECC40 is rimlock socket.Are they still around?
I guess mig-ru wants a dual triode with more then just a bit of the gain normally required since I suspect he wants to feed his line source directly to the log-pot? (Integrated stereo amp?)
I have a 2A3 integrated amp at home wich is fed directly from a 12ax7,it can be done but is admittedly not ideal.
A 6/12SL7 would probably be a viable compromise since it is better documented than most of the Rusky stuff,gain can be reduced and rp is lower than say 12ax7 and there is still plenty around ?
Cheers,
Bernhard,
With all due respect ; the E80CC is by far one of the best choices here on paper but EXPENSIVE !
( I know you're sitting on a couple of hundreds of them,still...)
ECC40 is rimlock socket.Are they still around?
I guess mig-ru wants a dual triode with more then just a bit of the gain normally required since I suspect he wants to feed his line source directly to the log-pot? (Integrated stereo amp?)
I have a 2A3 integrated amp at home wich is fed directly from a 12ax7,it can be done but is admittedly not ideal.
A 6/12SL7 would probably be a viable compromise since it is better documented than most of the Rusky stuff,gain can be reduced and rp is lower than say 12ax7 and there is still plenty around ?
Cheers,
hmm well what i was tryin to do with this amp is first of all design one (with help from others), and do somethin original (hence my original choice for preamp being 12A-7 tubes). ive seen both 6SN7 parallel and series setup and 6SL7 setup on the net. if i use those setups that would deem this whole project unnecessary. so my question is what if i add another stage say a 6SL7 after the 6SN7? would that work?
A 6SN7 followed by a 6SL7 again would work, but now it would have way too much gain. Additionally, there may be some headroom problems with the 6SL7. The 6SL7 biases at around 2V, which means it can only handle signals of somewhat less than 2V peak. Your CD player already puts out that much signal. That means the 6SN7 in between your CD player (or preamp) and the 6SL7 wont do anything other than add gain you will throw away in your volume pot. If you turn the volume pot up too high, the output of the 6SN7 will clip the input of the 6SL7, which is something you do not want. If anything clips in a tube amp, it should always be the output valve.
Dmitry,
if you add another stage in a feedback less design, this has way too much gain then as the gain of both stages is multiplied.
The design of the Kismet amp looks really nice to me, just i would not use an ECC88 but i would use a tube having a gain of about 30 and proven for audio and particular for full swing which the ECC88 IMO is not, it produces too much k3, trnasfer characteristics is bent negatively.
If i would be you, i would build the kismet amp and replace the ECC88 by the ECC40 and we all help you with eventual re-dimensioning of component parameters.
Frank,
E80CC is expensive (not for me, i have about 50 red Valvo in stock) but a good 2A3 is expensive, too.
ECC40 can be bought NOS for $5 to $20 on ebay. And Rimlock sockets should not be the challenge.
I must trust those who tried it out: ECC40 is preferred to E80CC.
E80CC is unbelievably relaxed and smooth as far as PRaT is concerned. ECC40 is even a bit more musical, tone colours are super-lush. As with the '56, both are IDHT with cylindric plate shape.
if you add another stage in a feedback less design, this has way too much gain then as the gain of both stages is multiplied.
The design of the Kismet amp looks really nice to me, just i would not use an ECC88 but i would use a tube having a gain of about 30 and proven for audio and particular for full swing which the ECC88 IMO is not, it produces too much k3, trnasfer characteristics is bent negatively.
If i would be you, i would build the kismet amp and replace the ECC88 by the ECC40 and we all help you with eventual re-dimensioning of component parameters.
Frank,
E80CC is expensive (not for me, i have about 50 red Valvo in stock) but a good 2A3 is expensive, too.
ECC40 can be bought NOS for $5 to $20 on ebay. And Rimlock sockets should not be the challenge.
I must trust those who tried it out: ECC40 is preferred to E80CC.
E80CC is unbelievably relaxed and smooth as far as PRaT is concerned. ECC40 is even a bit more musical, tone colours are super-lush. As with the '56, both are IDHT with cylindric plate shape.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.