I am TORN between Tube power amp and SS power amp.

If you like heat and replacing power tubes every 6 months then go with tubes.I like a SS amp that sounds the same every day i had tube amps such as CJ premier 5s,ARC d150 etc. Im very happy with solid state however i do have a tube phono stage and love it.Good luck though!

Uh, I think replacing power tubes every 6 months is a bit of an exaggeration. Maybe I'm just lucky but I haven't had that experience.
But anything is possible.

No experience with the amplifiers you mention but the Hafler, if in good working condition and no issues would be my choice.

I grew up during a time when there were no SS audio gear.  Sure I've had my share of SS amps but I prefer the sound of a SET amp.

Tubes every 6 months? I've had power amp tubes last for years!

Depends on the amp and the reliability of the tubes in some amps they can last over one year or more.What about when tubes blow out this happens.

I took a look at the manual for the Hagerman Clarinet line stage. It has a very high specified output impedance of 3K. That is most likely the output impedance at a mid-range frequency such as 1 kHz, and I see in the schematic that the design utilizes a 1 uF coupling capacitor at its output. A 1 uF capacitor has an impedance of about 8K at 20 Hz, which will result in an overall output impedance at 20 Hz that approaches 11,000 ohms!

That will make the Clarinet unsuitable for use with many and perhaps the majority of solid state amps, as well as with more than a few tube amps. I see that the stock DH500 has an input impedance of 47K, which would result in deep bass response with the Clarinet that is marginal at best (assuming that your speakers have reasonably good deep bass extension themselves; otherwise you might not notice the issue). If the upgrade you referred to would result in a reduction of that input impedance, I wouldn’t even consider it.

I know nothing about the VTA ST-120, but before deciding on it I would certainly inquire as to its input impedance. IMO 100K or more would be optimal, and as I said 47K is marginal at best.

Finally, you didn’t mention what speakers you will be driving. Its characteristics (including impedance, impedance variation over the frequency range, and sensitivity) will of course be important considerations in choosing an amp.

Good luck. Regards,
-- Al

I am running JBL L100 (Alnico, straight line speakers). In the manual, it says sensitivity is 78dB/1w @ 15 feet. I read somewhere that it is equivalent to 90-91 dB/1w/1m. VTA ST-120 has 270K Ohm input impedance. I have been thinking about (http://www.elekit.co.jp/en/product/TU-8600) SET 300B amp to run with my preamp and JBLs.

I spent my teens with my brothers L100's and later with a set of my own.  They were party monsters with 100 wpc solid state Pioneer amps.  Great speakers for that but no need for tubes IMO because finesse and detail isn't in their vocabulary anyway.  The new 2018 L100's may be a different story.

rodulfo, the SET amp you mentioned raises three red flags; input impedance of 50K ohms, 9.2 wpc power, and the weight of ~25lbs. Normally the weight of a SET 300B is a good indication of the quality of the transformers which are the most critical (and expensive) component of the unit. And the 9.2 wpc will be just enough to tickle the woofers on the L100. 

I am running JBL L100 (Alnico, straight line speakers). In the manual, it says sensitivity is 78dB/1w @ 15 feet. I read somewhere that it is equivalent to 90-91 dB/1w/1m.

That is correct. For a box-type (non-planar) speaker it can be calculated that 78 db/1w/15 feet corresponds to 91 db/1w/1m.

However I agree with the red flags cited by Kalali, and unless you listen exclusively at low volumes and to recordings having narrow dynamic range a 9 watt SET will not be powerful enough for 91 db speakers.

I assume from the quoted statement, btw, that your speakers are original L100s, not the "L100 Classic" that apparently is being produced currently. The latter having specs of 90 db/2.83 volts/1m and a 4 ohm nominal impedance, which corresponds to only 87 db/1 watt/1m.

I couldn’t find an impedance curve for the original L100, that would show how its 8 ohm nominal impedance varies over the frequency range. But the VTA ST-120s relatively high damping factor (for a tube amp) of 16, which at least theoretically corresponds to an output impedance for an 8 ohm tap of 8/16 = 0.5 ohms, suggests that it is likely to be able to interact with the speaker’s impedance variations in a reasonable manner. And its 270K input impedance would certainly be a suitable match for your line stage.

Also, I found the listing you referred to for the DH-500 upgrade, and I see that the upgraded amplifier has a specified input impedance of only 33K, rather than the 47K of the original. I would definitely not pair a 33K input impedance with your line stage.

So while I haven’t researched comments on the sonics of the ST-120, if those are encouraging that amp would seem to me to be the clear choice among the three possibilities you cited.

Good luck. Regards,
-- Al

P.S: I would add a fourth red flag to the three that Kalali cited for the SET amp. Its 9.2 watt power rating is based on THD (total harmonic distortion) of 10%!!   So it is likely to be a significantly less powerful amp than a 9.2 watt rating would usually suggest.

Regards,
-- Al

My 91db speakers sounded fabulous and played plenty loud and clear with a Dennis Had 12 watt (or maybe 17 watts...not sure) per side amp, but I switched to 99db Klipsch Heresy IIIs mostly to keep Almarg happy, as I deign to avoid his ire. 

:-)

Best regards,
-- Al

If the 91dB mentioned above is the sensitivity, then all that speaker needs is 1 watt to produce 91dB sound level at 1 meter. So there's no surprise that a 12 wpc amp can and will sound loud (clear is a subjective term) enough in a moderately small room. Other factors, which one could argue that are more important, are the speaker's efficiency as well as the way its impedance behaves across its frequency spectrum. Throw a piece of content with wide dynamic range and lots of transients, something like a large orchestral western classical music content, and the weaknesses become glaringly clear. Vocals, single instrumentals, and small bands like jazz trios, etc., not so much. 

Thank you very much for your informative replies. Especially to you #almarg and #kalali. You are very helpful guys! I really appreciate your feedback.

Cheers!🙂

I run both a solid state phono stage generally viewed as one of the best ever made, and a tube phono stage (CJ Premier 15).  Both give satisfaction.

Suggest that you seek out a good sounding phono stage and not worry about what the internals are.

   Hi Rodulfo, I have a pair of JBL 4312A’s on Sound Anchor stands . They are currently in the closet as I went to low power tubes . Your speakers need 100 plus wpc tube or 200 wpc SS . I’ve run these along with  my long gone Century 100’s using Dynaco MKIII’s ( 60 wpc ) , ASL 30 wpc ( El 34’s) Sansui 9090db, Bryston 4BSST, Yamaha RX-V, Modwright KWI-200. So with tubes , 30 wpc was too little and 60 was just starting to cut it . The Yamaha was 105 wpc ( but home theater stuff ) so not good. The Modwright had good control , but was dry . The Bryston was great ( so maybe the Hafler would be nice) . I contacted Quicksilver and they recommended their 120 wpc amps . Most people underestimate how much power the JBL’s need . Also too little power leads to clipping damage . I would go with SS for simplicity, but it might be too dry for your taste. This is a good speaker for a tube pre and a SS amp , or a big tube amp. I’m actually considering the Latino 120 wpc Monos . FWIT many people bi-amp the big JBL’s with tubes on top and SS for the woofers ( sometimes class D). But that’s a whole different beast , but due to the large power requirements. Many of us are willing to deal with the hassle of tubes because the result can be stunning with vintage JBL’s . BTW I also have Klipsch Heresys, but prefer the JBL’s . Happy Hunting, Mike. 

  Also , I have a Had Inspire on right now . At 12 WPC , don’t even try to run the JBL’s . That’s why I have Heresys and KG 1.5’s to supplement  my Zu’s . 

My 12 WPC Had Inspire with 99db (allegedly) Heresy IIIs is the real deal. Everyone should own this sort of thing at some point, but Had only makes one every couple of weeks so maybe it's not possible. I run this amp a lot...background music while working, frontground music when seriously actively listening, and as a backup toaster, although the crumbs from the toast are problematic at times.