IMO, the best sounding tube is EL11 - only Telefunken in triod in SE with power about 1-1.5 W. Very specific and unique amazing sound /there are two tubes in the word - EL11 Telefunken and others!/.
You try any projest on 71a triode?
I'm surprised that it hasn't been mentioned yet. My favorite tube for low powered amps is the 45. I wired a pair of 32 ohm headphones directly to the speaker outputs on a new test board for the TSE-II that I'm working on. I was stunned by the sound quality. Also tried the 2A3's and 300B's in the same amp, and I do prefer the 300B when you need to push some inefficient speakers around, but the 45 excels in the 1 watt or less department.
A triode connected 6V6GT is another good choice.
Low power? I can squeeze 35 to 40 watts from a pair of those......you just have to ignore all those numbers in the tube manual.....except for the screen grid voltage. Respect that spec or your tubes will not be happy.
The data sheet shows a triode connection spec of 300 volts. That's true ONLY in TV vertical sweep operation. Run them in triode at 300 volts in an audio amp, and leave the amp on a lot at low volumes or idle, and the tubes will eventually go into red plate runaway. This true for most TV sweep tubes.
TV sweep use runs at full "volume" all the time, hence a lot of the energy sent into the tube gets turned into 60 Hz or 50 Hz power, so less is dissipated in the tube. A class A audio amp at zero volume burns ALL the plate and screen power up in the tube as heat.
Run them in pentode at a screen voltage of 120 to 150 volts or so and they will live forever and sound nice. Plate voltage can be anywhere from 150 volts to 400 volts without problems. I had two different tubes run away in SE triode at around 300 volts. I haven't tried them at lower voltages, but the book mentions 225 volts. Probably a good place to start.
Note the 6W6 guts have been used in a lot of different tubes over the years. The 6W6, 6DG6, 12L6, 12EN6, 25W6, 25L6, 50L6, 6GC5, and a few more that I can't remember now ALL have the same internal parts and differ only in heater voltage or base. The specs may differ a little due to their intended use, but the curves all match.
The 6L6 is obviously bigger, and the 35L6 is an underpowered oddball created to allow for more tube heaters to be wired in series across the AC line when FM radio came into existence.
A triode connected 6V6GT is another good choice.
Low power? I can squeeze 35 to 40 watts from a pair of those......you just have to ignore all those numbers in the tube manual.....except for the screen grid voltage. Respect that spec or your tubes will not be happy.
The data sheet shows a triode connection spec of 300 volts. That's true ONLY in TV vertical sweep operation. Run them in triode at 300 volts in an audio amp, and leave the amp on a lot at low volumes or idle, and the tubes will eventually go into red plate runaway. This true for most TV sweep tubes.
TV sweep use runs at full "volume" all the time, hence a lot of the energy sent into the tube gets turned into 60 Hz or 50 Hz power, so less is dissipated in the tube. A class A audio amp at zero volume burns ALL the plate and screen power up in the tube as heat.
Run them in pentode at a screen voltage of 120 to 150 volts or so and they will live forever and sound nice. Plate voltage can be anywhere from 150 volts to 400 volts without problems. I had two different tubes run away in SE triode at around 300 volts. I haven't tried them at lower voltages, but the book mentions 225 volts. Probably a good place to start.
Note the 6W6 guts have been used in a lot of different tubes over the years. The 6W6, 6DG6, 12L6, 12EN6, 25W6, 25L6, 50L6, 6GC5, and a few more that I can't remember now ALL have the same internal parts and differ only in heater voltage or base. The specs may differ a little due to their intended use, but the curves all match.
The 6L6 is obviously bigger, and the 35L6 is an underpowered oddball created to allow for more tube heaters to be wired in series across the AC line when FM radio came into existence.
+1.
The 45 is my first choice too. The 46 is very very close....
The nice thing about the 45 which is quite rare in power tubes is its really low microphonic. That is likely one of the reasons for its well earned reputation as good sounding tube.
For really low power (suitable for headphone amp) I like the 49. This is also a fine very linear driver for 45, 46, 2A3 and similar...
The 45 is my first choice too. The 46 is very very close....
The nice thing about the 45 which is quite rare in power tubes is its really low microphonic. That is likely one of the reasons for its well earned reputation as good sounding tube.
For really low power (suitable for headphone amp) I like the 49. This is also a fine very linear driver for 45, 46, 2A3 and similar...
I have compared the 71a, 45, and 2a3.
The 2a3 is kind of a weird tube right now. I only like the RCA single plate 2a3 and they cost about as much as a used car. The chinese 2a3s are supposedly all 300b tubes that have a lower voltage heater and they don't sound like a 2a3 IMO.
IDK if any 3rd party company has made something similar to a true single plate 2a3 that costs less than 300 a pair.
The 45 is just a fantastic tube. Super clear. Holographic. And it can have really powerful bass if you use the right transformer.
The 71a is probably my favorite for headphone use. It is a lot warmer sounding than the 45 and it has a certain amount of weight and fat to the bass that the 45s just don't have. As a result, the 71a ends up matching really well with a large array of headphones that have slightly weaker bass.
The 2a3 is kind of a weird tube right now. I only like the RCA single plate 2a3 and they cost about as much as a used car. The chinese 2a3s are supposedly all 300b tubes that have a lower voltage heater and they don't sound like a 2a3 IMO.
IDK if any 3rd party company has made something similar to a true single plate 2a3 that costs less than 300 a pair.
The 45 is just a fantastic tube. Super clear. Holographic. And it can have really powerful bass if you use the right transformer.
The 71a is probably my favorite for headphone use. It is a lot warmer sounding than the 45 and it has a certain amount of weight and fat to the bass that the 45s just don't have. As a result, the 71a ends up matching really well with a large array of headphones that have slightly weaker bass.
You are welcome.
I also had a project with 5W output, but used 2 in parallel with 2k5 load.
One more 4P1L SE
4P1L is not "worst", it is a gorgeous tube, one of the best.
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