May be we can use 4 pairs of 2A3's to get 40Watts output. The output transformer should be rated for 250mA idle current.
Also, we need a 2 x 2.5V 10A for the 2A3's filament supply.
The price of 2A3 is not cheap at all.
I would rather just use 2A3 in singled end amplifier that gives me 3.5W sweet and beautiful sound...
Johnny
Also, we need a 2 x 2.5V 10A for the 2A3's filament supply.
The price of 2A3 is not cheap at all.
I would rather just use 2A3 in singled end amplifier that gives me 3.5W sweet and beautiful sound...
Johnny
The 2A3-40 by JJ is a very good tube.It is very stable and not so difficult to select; I have Sofia.
At this link:
http://www.multitask.it/diy/fabfour.JPG
you can see the first prototype of a pair of amps using these tubes.
This is a second version (for my friend):
http://www.multitask.it/diy/1000eniumab.jpg
The rms power is 45 w - 8 ohm and 60 w at 4 ohms; impulsive around 75 w.
It works for the 40% in class A.
Bye
Walter
At this link:
http://www.multitask.it/diy/fabfour.JPG
you can see the first prototype of a pair of amps using these tubes.
This is a second version (for my friend):
http://www.multitask.it/diy/1000eniumab.jpg
The rms power is 45 w - 8 ohm and 60 w at 4 ohms; impulsive around 75 w.
It works for the 40% in class A.
Bye
Walter
Correct, the 2A3-40 is a 300B with a 2,5 v filaments.
The good thing is that it can be powerd with ac on fil. and the hum is very low.
In my last amp the noise at the otuput was abou 0,45 mv without Feedback. Same project with 300B are 0,7-0,8 mv.
I am able to send, ASAP, the curves of this tube from my Sofia .
Bye
Walter
The good thing is that it can be powerd with ac on fil. and the hum is very low.
In my last amp the noise at the otuput was abou 0,45 mv without Feedback. Same project with 300B are 0,7-0,8 mv.
I am able to send, ASAP, the curves of this tube from my Sofia .
Bye
Walter
3nity said:
There may be a way to get about 35 watts at the expense of
distortion and damping factor. Check out the SE op point at 450V
anode and 80 mA into 2000 ohms. Class A (more or less) push-pull
at this op point and 4000 ohms plate-plate would give you about
35W at the anodes and well over 30W out after losses. The anode
dissipation will be 36 watts at idle.
The chart is for a 300B but the JJ 2A3-40 has the same characteristics.
For a 4 ohm speaker you just need a 4000 ohm to 4 ohm OPT.
Michael
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Josepmaria78. Please re-post in English. diyAudio is an English language forum. Thanks!
So what else is new? For many years, manufacturers have been stuffing tubes with whatever they've got in order to meet demand. We've seen 6AQ5 pinned and stuffed into metal tubes as 6V6. There are darn fine 6L6GC sold in the "wrong" pinout as 6BG6GA. We've seen 6AV5 packaged and sold as 6B4. While I'm on it, what the heck is the monoplate Sovtek 6B4G anyway? It sure ain't a fifteen watt tube.
There's precious few new things under the sun. Anything that could be done with a tube has already been thought by someone else, and tried by ten others. Personally, I'd think most people would be happy to get 300B levels of performance from a 2A3 rated tube. If only they could keep the prices to 2A3 levels as well...
Hey Ty,
I admit nothing is new as we have numerous examples of misleading specs. The new thing is that a reputable "hifi" tube manufacturer does the same. I can see why they did it as they have either paralleled or series connected the heaters.
If you read the whole answer you will see why I complained: JJ publishes RCAs curves for 2A3.
About Sovtek, have you check ir they are 300B in disguise or 2A3 with higher rating? Would be nice if the latter is true. I vagely remember seing some curves here at diyaudio showing better linearity around the recommended 250V Ua. Must admit I haven´t checked 300B at the same Ua. They might be quite alike
.
About "to get 300B levels of performance from a 2A3" I personally prefer the original 2A3 as performing better, albeit not having the higher Pa. For all of us just a matter of taste.
I admit nothing is new as we have numerous examples of misleading specs. The new thing is that a reputable "hifi" tube manufacturer does the same. I can see why they did it as they have either paralleled or series connected the heaters.
If you read the whole answer you will see why I complained: JJ publishes RCAs curves for 2A3.
About Sovtek, have you check ir they are 300B in disguise or 2A3 with higher rating? Would be nice if the latter is true. I vagely remember seing some curves here at diyaudio showing better linearity around the recommended 250V Ua. Must admit I haven´t checked 300B at the same Ua. They might be quite alike
.About "to get 300B levels of performance from a 2A3" I personally prefer the original 2A3 as performing better, albeit not having the higher Pa. For all of us just a matter of taste.
I think 40W is barely approachable in class A with a 40W anode dissipation limit, and that with an asymmetric load line. The best I can imagine in A2 is about 38W with a 2K per side (4K plate-plate) load impedance, and whether it qualifies for class A is debatable.
I personally would rather shoot for 20-25W power output with decent damping factor and reasonable distortion in A2, and 15-20W in A1
I personally would rather shoot for 20-25W power output with decent damping factor and reasonable distortion in A2, and 15-20W in A1
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