I have used many different types of 2a3's all using AC heating and have had no audible hum.
Really, a big range from WW2 tubes to cheap Chinese ones from the 1990's. Used monoplate sovteks as well. Noting too expensive mind you....
2a3's AC heater hum is audible however if you are building a headphone amplifier.
Ian
I might add this: I used to use very inexpensive filament transformers and always had a tiny bit of hum. Then one day I was visiting Thomas Mayer (vinylsavour) and bought a couple of his filament transformers.
Wow.. The tiny bit of hum I had disappeared. My "living voice" speakers have 96dB sensitivity.
Ian
Wow.. The tiny bit of hum I had disappeared. My "living voice" speakers have 96dB sensitivity.
Ian
Regarding 2a3 vs. 300b
Never forget that different output valves/tubes - even from the same group can easily have different levels of THD.
I recently went through my bunch of cheap Chinese 2a3's and thought that I had selected a more-or-less decent pair, but testing (with kind assistance of another member here) showed one channel with a full 1% more THD than the other. This is significant (!) Swapping 2a3's between channels showed that it completely down to the selected 2a3.
Look at the RCA 2a3 specs sheet and you will see 5% quoted for second order harmonic distortion when run class A1 for 3.5 Watts at 250V on the plate (60mA).
I tend to run 2a3's single ended A1 at lower current than on the RCA specs sheet (50mA vs. 60mA), and I use a 3.5k load instead of 2.5k - basically to try and get the THD down and because I don't need so much power. I have also done PP 2a3 amps in the past and will probably build them again soon since I recently acquired some nice suitable Tango OPTs again... 😀
Anyway, with some talented assistance, my one Chinese 2a3 "sample" showed 2.5% THD while another showed 3.5% THD. These were already pre-selected for low noise and similar 'good' characteristics out of my stash of cheap-n-terrible 2a3 china tubes. Something like 98% of the THD was second order harmonics.
We did not test any other 2a3's at the time, nor did we did any testing on the input/driver stage which most certainly adds something of its own. I have a pretty good feeling that the RCA specs sheet values are reliable.
For 300b the quoted THD in the Bell specs sheet for single ended A1 drive is 5% so is very similar to 2a3, but you will get 6-8 Watts.
Its of course fair to say that a well designed push-pull 2a3 will beat a single ended 300b in terms of THD. But are we comparing like with like?
Ian
Never forget that different output valves/tubes - even from the same group can easily have different levels of THD.
I recently went through my bunch of cheap Chinese 2a3's and thought that I had selected a more-or-less decent pair, but testing (with kind assistance of another member here) showed one channel with a full 1% more THD than the other. This is significant (!) Swapping 2a3's between channels showed that it completely down to the selected 2a3.
Look at the RCA 2a3 specs sheet and you will see 5% quoted for second order harmonic distortion when run class A1 for 3.5 Watts at 250V on the plate (60mA).
I tend to run 2a3's single ended A1 at lower current than on the RCA specs sheet (50mA vs. 60mA), and I use a 3.5k load instead of 2.5k - basically to try and get the THD down and because I don't need so much power. I have also done PP 2a3 amps in the past and will probably build them again soon since I recently acquired some nice suitable Tango OPTs again... 😀
Anyway, with some talented assistance, my one Chinese 2a3 "sample" showed 2.5% THD while another showed 3.5% THD. These were already pre-selected for low noise and similar 'good' characteristics out of my stash of cheap-n-terrible 2a3 china tubes. Something like 98% of the THD was second order harmonics.
We did not test any other 2a3's at the time, nor did we did any testing on the input/driver stage which most certainly adds something of its own. I have a pretty good feeling that the RCA specs sheet values are reliable.
For 300b the quoted THD in the Bell specs sheet for single ended A1 drive is 5% so is very similar to 2a3, but you will get 6-8 Watts.
Its of course fair to say that a well designed push-pull 2a3 will beat a single ended 300b in terms of THD. But are we comparing like with like?
Ian
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Lots of replies and educational, thanks. I'm a noob at building and haven't a clue about schematics. Basically a kit builder if you may. The last one I put together was George Andersons TSE designed around 45's using Electra Print Iron. Got to stay busy and would like to do another pwr amp. I've done a few Bottleheads and a few phono preamps.
I'm not a tube fanatic, but I know that the original WE300B is very very special. A friend of mine once demonstrated real WE300B vs Japanese 300B, and there was a surprising difference. I guess 300B legend is based on the original WE tubes that surely have a magical quality.
Hi, Have question from a friend please.
if you use JJ2A3/40 at 2A3 operating points, should it sound as a 2A3 - even though it is actually a 300B with 2.5v filament - and if operated as 300B (as JJ do themselves in their 10W '2A3' commercial amplifier) - does it then sound like a 300B?. In other words, do the operating conditions have more impact on the resultant sound that the absolute tube type itself? - and before jumping to the obvious that it is a 300B with 2.5v filament with 40W plate - has anyone tried running a true 300B at 2A3 operating points ?
regards
if you use JJ2A3/40 at 2A3 operating points, should it sound as a 2A3 - even though it is actually a 300B with 2.5v filament - and if operated as 300B (as JJ do themselves in their 10W '2A3' commercial amplifier) - does it then sound like a 300B?. In other words, do the operating conditions have more impact on the resultant sound that the absolute tube type itself? - and before jumping to the obvious that it is a 300B with 2.5v filament with 40W plate - has anyone tried running a true 300B at 2A3 operating points ?
regards
Hmm, sounds like a lot of hearsay here. I've built dozens of 300B amplifiers over the years, both SE and PP. They're only euphonic in badly designed circuits in my experience.
Their linearity is amongst the best I've measured and the old WE curves show this pretty clearly. A modern 300B that delivers that promise IMO surprisingly is the JJ 300B. (And yes I've compared it to NOS WE 300B which were slightly better at 5X the price.)
I much prefer them to the 2A3 which in itself is not a bad tube if you need more power than a 45 will provide.
My favorite DHTs currently are the GM70, 300B (JJ, EML), EML 20AM, and the 45 (Sylvania or RCA)
I suppose the 300B bashing arises out of the fact that there is a lot of hype around them and therefore they tend to be expensive. The cheap ones aren't particularly good. The JJ 300B IMLE will run 10000 hours before needing replacement so that's not too bad.
Their linearity is amongst the best I've measured and the old WE curves show this pretty clearly. A modern 300B that delivers that promise IMO surprisingly is the JJ 300B. (And yes I've compared it to NOS WE 300B which were slightly better at 5X the price.)
I much prefer them to the 2A3 which in itself is not a bad tube if you need more power than a 45 will provide.
My favorite DHTs currently are the GM70, 300B (JJ, EML), EML 20AM, and the 45 (Sylvania or RCA)
I suppose the 300B bashing arises out of the fact that there is a lot of hype around them and therefore they tend to be expensive. The cheap ones aren't particularly good. The JJ 300B IMLE will run 10000 hours before needing replacement so that's not too bad.
Hello Thomas
What is total max rms output power from single ER300B ?
Are they 10, 8 or 6~5 watts...or ?
Just share link to Diyer who search for his new amp build project
interesting tubes candidates like 300B triodes.
Best regards 🙂
Hi Kevin
Absolutely nothing wrong with the 300b in my books. Only two things I would make sure to consider: regulated DC heaters and a really good low impedance driver.
Every "euphoric" sounding 300b amp I have witnessed (including every single one from china) has had a mediocre driver circuit.
Ian
Absolutely nothing wrong with the 300b in my books. Only two things I would make sure to consider: regulated DC heaters and a really good low impedance driver.
Every "euphoric" sounding 300b amp I have witnessed (including every single one from china) has had a mediocre driver circuit.
Ian
Agree 100% with both comments Ian. Both are very important issues as is power supply design quality. I like stiff low impedance supplies whether regulated or not.
Depends
I am no engineer or expert, but since I have been running 300b amps of varying designs in the same system, I guess I have some standing. At present, I have three 300b amps running in the system with an active crossover. They are all amps designed by Kevin Kennedy.
The bass channel is an older design, but is heavily tube regulated with transformers that are nothing exotic. It drives two 15 inch Westrex drivers per channel. The two new 300b amps are driving Vitavox S2 horn drivers. The other amp is driving Fostex T500A tweeters, soon to be replaced with Raal ribbons, assuming they play nicely with the other drivers.
As a basis of reference, I also drove this system with JE labs Deluxe units with Tamura permalloy outputs. That was the least acceptable sound. Quite poor actually. Then, I used Kevin's 300b which was a huge improvement and very nice sounding. But of course, the curse of this hobby is we are never content to leave well enough alone.
The new mid and high 300b amps use a D3A driver, amorphous interstage transformer and amorphous output transformer all made by Monolith Magnetics in Belgium. The sound improvement t is quite huge, and is due undoubtedly to a great design and good components. Not cheap, but anything truly good is not.
The takeaway is that the 300b is a good solid tube and the ultimate sound is dependent on design, parts and build. Even the best tube in the world, if there's such a thing, would sound like crap if the amp is not designed and built properly. These JJ 300b tunes are excellent in terms of sound, quality and cost. Assuming your speakers are high efficiency and relatively easy to drive, it is simply hard,to beat a good 300b amp. And yes, I have had push pull KT 88 amps driving monkey coffin speakers, and in no way did they approach the sound of a good 300b amp.
I am no engineer or expert, but since I have been running 300b amps of varying designs in the same system, I guess I have some standing. At present, I have three 300b amps running in the system with an active crossover. They are all amps designed by Kevin Kennedy.
The bass channel is an older design, but is heavily tube regulated with transformers that are nothing exotic. It drives two 15 inch Westrex drivers per channel. The two new 300b amps are driving Vitavox S2 horn drivers. The other amp is driving Fostex T500A tweeters, soon to be replaced with Raal ribbons, assuming they play nicely with the other drivers.
As a basis of reference, I also drove this system with JE labs Deluxe units with Tamura permalloy outputs. That was the least acceptable sound. Quite poor actually. Then, I used Kevin's 300b which was a huge improvement and very nice sounding. But of course, the curse of this hobby is we are never content to leave well enough alone.
The new mid and high 300b amps use a D3A driver, amorphous interstage transformer and amorphous output transformer all made by Monolith Magnetics in Belgium. The sound improvement t is quite huge, and is due undoubtedly to a great design and good components. Not cheap, but anything truly good is not.
The takeaway is that the 300b is a good solid tube and the ultimate sound is dependent on design, parts and build. Even the best tube in the world, if there's such a thing, would sound like crap if the amp is not designed and built properly. These JJ 300b tunes are excellent in terms of sound, quality and cost. Assuming your speakers are high efficiency and relatively easy to drive, it is simply hard,to beat a good 300b amp. And yes, I have had push pull KT 88 amps driving monkey coffin speakers, and in no way did they approach the sound of a good 300b amp.
The choice is just a matter of desired power.
For SE operation I prefer the 300B if the target is 20-25W. It will be a PSE of course. For 9-10W I prefer the 2A3 PSE. I have built a few 300B SE amps and they work fine if properly designed but the 2A3/6C4C PSE is so much more convenient in all areas (power supply, ouput transformer, drive, cost....).
The 45 is my beloved tube but I have not used it in SE since a long time. I was able to buy 3 new quads (RCA, Raytheon, Sylvania) each made of identical tubes about 10-15 years ago when there were still a good number around at reasonable prices and I will not "waste" them in SE. Of course I am sure they are new (one is not anymore but still doing fine) as I have tested them even on curve tracers. I only use the 45 in PP class A. For SE and that sort of power (i.e. up to 2.5-2.8W output) I use the 46 which is just as good. If I want 4-5W I use a 2A3.
Regardless of filament voltage I only use DC supply. Intermodulation is the evil as already said by others.
For SE operation I prefer the 300B if the target is 20-25W. It will be a PSE of course. For 9-10W I prefer the 2A3 PSE. I have built a few 300B SE amps and they work fine if properly designed but the 2A3/6C4C PSE is so much more convenient in all areas (power supply, ouput transformer, drive, cost....).
The 45 is my beloved tube but I have not used it in SE since a long time. I was able to buy 3 new quads (RCA, Raytheon, Sylvania) each made of identical tubes about 10-15 years ago when there were still a good number around at reasonable prices and I will not "waste" them in SE. Of course I am sure they are new (one is not anymore but still doing fine) as I have tested them even on curve tracers. I only use the 45 in PP class A. For SE and that sort of power (i.e. up to 2.5-2.8W output) I use the 46 which is just as good. If I want 4-5W I use a 2A3.
Regardless of filament voltage I only use DC supply. Intermodulation is the evil as already said by others.
Ok, As I have understood it, the products of intermodulation distortion are typically odd-order (3rd and 5th order) harmonics. Please correct me if I am wrong.
Ian
Ian
One effect of AC filaments on DHTs, is that one end of the filament or the other end of the filament gets closer to the grid 120 times a second (60 Hz AC power).
Yes, the other end is getting further away as the one end is getting closer, so there is some cancellation of this effect.
But you will see 120Hz sidebands on Every spectral line of the test tone(s).
For example, a 1 kHz test tone will now have 880 Hz and 1120 Hz tones appearing on it.
And it is the same effect for other tones of the signal generator (or the music).
I consider this to be a more important effect, than a few millivolts of 60Hz or 120Hz hum.
We could even see it on an HP 3585 spectrum analyzer even though the test tones were small amplitude.
Yes, the other end is getting further away as the one end is getting closer, so there is some cancellation of this effect.
But you will see 120Hz sidebands on Every spectral line of the test tone(s).
For example, a 1 kHz test tone will now have 880 Hz and 1120 Hz tones appearing on it.
And it is the same effect for other tones of the signal generator (or the music).
I consider this to be a more important effect, than a few millivolts of 60Hz or 120Hz hum.
We could even see it on an HP 3585 spectrum analyzer even though the test tones were small amplitude.
Hmmm. I have heard this arguement before. Sorry if I sound skeptical.
However would this this also not apply to B+ ripple?
What if B+ ripple and filament ripple were of of the same frequency and in phase with each other?
Ian
However would this this also not apply to B+ ripple?
What if B+ ripple and filament ripple were of of the same frequency and in phase with each other?
Ian
