What's the greatest bargain in SET these days?

I own two low-wattage pushpull amps: a 5 wpc amp using two 349 tubes per channel and a 4 watt amp using two 45 tubes per channel, and I own a parallel SET amp that puts out 6 wpc from two 2a3 tubes per channel. All of these amps deliver adequate levels of power for my 99 db/w speakers. I do suspect that I am hearing some slight compression from these amps running out of gas (sound becomes a bit muddled and lacking in clarity) only when I play choral music at high volume.

If the Reference speakers turn out to be substantially lower than 92 db/w in efficiency, there may be some concern with having adequate power from low-powered triode SETs, such as ones utilizing a 300b tube. SETs utilizing higher power tubes, such as the 845 or 211 tend to be a bit more costly and I would be a bit concerned with any "bargain" amp that is operated at the higher voltage levels required for such amps.

With respect to some of the amps mentioned above, I have heard the Art Audio PX 25 and Jota amps used with several different speakers and I like these amps; I don't know if they are "bargains," but they were good sounding. I have also heard an Audio Space pushpull amp that was very good for the money both in terms of sound and quality of construction. I heard two different Decware amps (I can't remember the models) that were in a shop as trade-ins. I only heard them briefly in a setup that was hardly optimized to show them off, so I don't have any sort of solid take on these amps; what I did hear was quite disappointing--too lifeless and wimpy sounding.

My experience with more reasonably priced SET amps is somewhat limited, but from what I have heard, it would not be that easy to achieve better sound from such amps than what the Manley Mahi will deliver without paying substantially more for the SET amp. Good SET amps are not cheap (output transformers have to be bigger and more expensive than pushpull transformers to perform well),and higher powered SET amps using transmitting tubes or parallel output tubes are particularly expensive.

Also, I would suggest trying an output transformerless (OTL) amp with the Reference speaker. While Reference speakers are already quite lively sounding, a good OTL would ramp that quality up even more and that would be something special.

Rebbi,

As long as you go into this venture with the right frame of mind--you are willing to experiment and accept an unfavorable result and willing to accept a bit of financial loss if the choice does not work out--I say by all means do the experiment. It might well be the case that you will enjoy the attributes of the low-powered SET with 95% of your music and will only have to accept some compromise with playing a few recordings. So many factors are at play that it is hard to predict the result and trial is absolutely necessary.

If the De Capo is easy to drive, that is actually more important than the efficiency rating. I have heard low wattage tube amps driving the very easy load 15 ohm Rogers LS3/5a speaker that is extremely inefficient (low 80's for efficiency) and the combination worked well even in a big room. On the other hand, the Wilson WP7 has a mid 90's efficiency, but even 40-50 watt tube amps would find that speaker to be a beast because of its very challenging load characteristics.

To me, the choice of the particular output tube being used is at least as important as the choice between single ended and pushpull. In either topology, the sound of the particular tube will come through and may be the difference between liking and disliking the result. In other words, if you happen to like a 300b SET amp, but, it turns out to not have quite enough power/control of the bass, consider a 300b pushpull amp in addition to looking for a SET alternative.

I haven't heard the alternatives you have been considering, except for the Art Audio PX-25. I like that amp. I actually prefer it to Jota (more delicate and beautiful sounding, though not as punchy), although the output power is quite low. I heard the PX-25 with very efficient Avantguarde speakers, and with much less efficient Spendor speakers and it is surprisingly capable for having a low output rating.

I do agree that, relative to a pushpull amp, SET amps tend to have less bass extension and "softer" bass (less impact or punch). But, I really like the "tuneful" nature of SET bass. I hear more subtle variations and tonal qualities to drums and lower bass instruments with SET amps than with most pushpull amps. In that sense, pushpull amps tend to sound a bit "mechanical" and that punch has a "sameness" no matter the music; one does not get that sense with SET amps. From my experience, there is no perfect choice and tradeoffs are involved. I like the tuneful bass of SETs, but, I also like the extra kick I get from my pushpull amps. These days I listen mostly to my pushpull 349 amp.

Rebbi, I hate to complicate your search even more, but, you really MUST listen to a good OTL amp. Given a high enough impedance speaker, OTLs can be VERY good. Something like the 30 watt Atmasphere would appear to be a good match.

Gsm18439,

Your comments about the sound of the 2a3 and 45 amp illustrate how important it is to hear these different tubes. Yes, the 2a3 and 45 ARE leaner sounding tubes. Both, particularly the 45, CAN actually deliver deeper bass than the 300b, but, neither have the big, fat, upper bass that so many listeners love about the 300b. Personally, I like the 2a3 and 45 more than the 300b because, in my system, the 300b sounds too bloated and lumpy in the bass range. I particularly like the 45, but for the very low output of that tube.

Rebbi,

If you are willing to take a little bit of a gamble, go with the interesting, low-cost alternatives mentioned here. If you want more of a sure thing, go with the Audionote kit. The kits are quite reasonably priced and Audionote provides good instructions on how to build them. I have heard most of their lineup of amps and they all sound very good. I have not heard a kit amp, but, a good friend of mine built their DAC4 kit and it is a particularly good DAC for the money.

I also like tube amps that don't go all out to maximize dissipation. Just backing off a little will increase tube life by a LOT. With my curren pushpull amps, it really is a very big deal that the amp runs the tubes conservatively. It utilizes four input/driver tubes that cost about $1,000 each and four output tubes that cost about the same. I am counting on the tubes lasting a very long time.

Charles1dad,

I certainly hope the tubes will last much longer. I would expect that running tubes conservatively will lower distortion and should sound better. However, I know of a number of people who deliberately run certain tubes quite "hot" and like it that way. For example, a friend runs 45 tubes in an Audionote Kageki (parallel 2a3 amp) and likes the sound, although the tubes don't last very long. I don't know if he just likes the sound of the 45 more than 2a3 (I prefer 45s too) and would actually be better off changing the operating parameters of the Kageki to match the 45 (primarily lowering the plate voltage). I own a pair of Kageki amps too, and would never run anyting but the recommended tubes for fear of damaging a VERY expensive amp.

As for the benefits to longevity of running stuff conservatively, there are plenty of examples of people who have old tabletop radios that are still being used daily that have never had tubes replaced since the radio first went into use in the 1940s and even earlier.

I have found, generally speaking, that changing the small signal tubes in an amp have a bigger impact on the sound than changing output tubes. This is good news because most of these tubes are cheaper than the output tubes. Although my Audionote Kageki came with some quite expensive RCA 6sn7s, I actually preferred alternatives such as Tungsol and Neotron roundplates. That amp is currently on loan to a friend who is now running CV181s (not exactly drop in replacements for 6sn7s, but close enough) and likes that tube a lot. I don't know what brand of CV181s these are, but, they are old (not Chinese) and are, I believe, cryogenically treated tubes from Pearl.