The 300B tube should last around 10 years and is the cleanest sounding of the group. KT-88 tubes last 3 or 4 years and have a warmer sound.
11 responses Add your response
Disclaimer: Just trying to help so be aware that this is very subjective and I've only been into tubes for about a year with limited experience.
Matching an amp (with various tubes) to a speaker with the appropriate sensitivity and characteristics is, I expect, an art and only comes with experience but here are some starting points that I found useful.
TUBE - AMP - POWER - SPKR - "SOUND"
2A3 - SET - 3.5 watts - 93dB - magic; refined
300B - SET - 7 watts - 90dB - magic; clear/natural
KT88/triode - P/P - 15 watts - 88dB - warm; solid
KT88/pentode - P/P - 25 watts - 86dB - ?
(P/P = push/pull design)
I started with ASL Wave 8 monoblocs (P/P) which are a great place to start (bang for buck and they're resellable). I tried KT88s in the AES Super Amp (P/P) and liked that better (Svetlanas were my favorite). I then got an AES SE-1 (SET) that can use either 2A3s or 300Bs. I liked the Sovtek 2A3s better than the 300Bs that came with the unit. Then I tried Sophia 300Bs (300/pr) and have found the sound I was looking for. Since the speakers I use have a sensitivity of 89dB, is reputed to be tube friendly, and I listen at moderate levels, the 300B has been a good match.
The main point I'd make is that I have enjoyed owning all three of these amps (and they satisfied my curiosity about these tubes you are asking about). Listen if you can to amp/speaker combinations before buying, but if you cannot (like me living in the sticks) stay with amps in your price range that have a good resale value here on Audiogon and enjoy.
Sorry for the confusion. I was referring to the AES Super Amp that I owned that was a push/pull design. It had 15w/ch in triode mode with KT88s. According to Divertech, the ASL MGSi15 DT is a SET design with KT88s. I have not heard that so I was trying to relate the KT88 sound that I had with my AES. The ASL will no doubt sound different using a SET design (hopefully have some SET magic).
I took another closer look at the Divertech site.
The ASL MGSi15 when running in triode mode is only 5w/ch. The 15w/ch is for pentode mode. If you want to use it in triode mode, you'll need fairly efficient speakers (say 92dB/w sensitivity) if you want more than polite levels. I'ver read some reviews that suggest pentode mode gives tighter bass but is not as refined as the triode mode (I never ran mine in pentode mode since it required an internal wiring change on the AES).
Before delving into the subjective differences in the three named tubes it might benefit us to answer the first question which is what are the characteristics of the three tubes. The 300B and 2A3 are true triodes or three element tubes, without getting too technical they consist of a cathode, a plate and a control grid between the two. When operated single ended the inherent distortion signature of these tubes is that distortion, although high, diminishes linearly as the harmonics of the fundamental increase. The KT-88 is a different beast. It is a beam power tube. A beam power tube is a pentode or five element tube; the elements are the cathode, control grid, screen grid, plate and supressor grid. The additional elements are used to collect and concentrate stray electrons flowing from the cathode to the plate into beams thus substantially increasing efficiency but, some would say, adversely affecting the distortion spectra of the tube. Such a tube, the 6550 is a similar power tube, can be operated without using the additional elements and then can be said to be a pentode tube operating as a triode. One problem with this is that the additional elements are still in the physical envelope of the tube and certainly affect the path of the electrodes from cathode to plate and are two more elements to resonate causing distortion. Although many would argue that the the distortion spectra of a pentode is subjectively improved by only connecting the three elements many also believe the the distortion spectra is still several orders of magnatude less consonant with the musical structure than true triodes.
Let's see if I get it correct:
So only real triode tubes are 2A3 and 300B, correct? And the rest are just a power tubes that can be operated in a triode mode or other mode?
Then for triode tube, it can be design to operate as single ended or push-pull.
Then the only truely SET amp are those using only 2A3 and 300B tubes? The rest is a psudo SET that is operated in triode mode (single ended) for other power tubes? The mauafacturers use the word "SET" just for their advertising purpose.
Please correct me if I am wrong,
Thanks a lot for all great explanation.
Ake: There are triode "power" tubes other than the 2A3 amd 300B such as 45's and 50's (quite a few more as well).
Yes, triodes can be configured as either (SE or push/pull).
For more info on tubes and their applications read the article @ this web address:
The manufacturer's that I am aware of only use the term "SET" for their true "single ended triode" designs and you may be thinking of "SE" (single ended) in this context for amps with one power tube per channel using EL34's, KT88's, et cetera.
As mentioned above 2A3 & 300B are not the only triode power tubes in use. There are various designs which are not true SET and/or push/pull, but the importance of any design is its reliability and how it sounds. IMO, there is nothing that sounds quite like a "good" SET design, but there are also many good SET designs that sound quite different from one another which would imply that much of a specific tube type's "characteristics" are dependent on the design of the circuit that they are used in (system matching aside). The only way to really experience/understand this is to audition and/or own them.
Ake: Excellent question and part of the difference is that ASL is running a pentode tube in triode mode. I am not very technical myself (though have been doing a little reading in order that I can refurbish my own tube gear) and my understanding is that the SE amps using pentode tubes (in triode mode) are not directly heating the output tubes. SET amps using "true" triode tubes are generally directly heated (which many feel creates a different type of sound).
Perhaps there should be another widely acknowledged designation for these amps (I know that Audion, in the UK, uses a different one for their models that use pentodes in triode mode)? Some tube amps seem to switch over to another mode @ a given output level (like certain SS amps) and these I do not understand @ all. I went to the Decware site and, yes, they use the term SET (though the amps are based on pentode tubes). I did not look @ ASL's site as I could not locate it.
I have only listened (seriously) to two amps that run Pentodes in SE triode mode (one being an early version of the Zen and the other is a small vintage SE EL84 amp that I currently own. Both of these sound different than push/pull to me, but without the added/flesh reality that I have heard from 2A3 and 300B SET amps. This could be due to the expense/build though as the true SET amps cost 2 to 6 times as much as the Zen, which retailed for $550 back then.
To make things even more confusing, I can easily modify the EL84 push/pull amp (which we are using in the living room) to push pull "triode" mode (it's currently running in push/pull pentode). Doing so will drop the power by half, or so, and alter its sound. I think that some of the ASL amps already come with such switching capability (pentode to triode), which might be nice to have.
I have forgotten the ASL designer's name, but he frequently answers questions in the audioasylum.com tube forums (they have separate "tube" & "SET" forums). You may find other owner's of the ASL models that interest you there as well. Also if you go to the FAQ section (@ the top of the main page) you will find the tube link that I listed as well as some nice "guidelines" for matching speakers to flea/fly watt amps (to be taken with a grain of salt as also noted in the article itself).
This still takes us back to the fact that you really need to hear the specific amps to understand their sound. The sound of these types of amps can be much more diversified than that of most SS electronics and if you are like me you will love some and hate others.