Tube power for KEF 104aB?

[Benjib]

I need help. I have never owned a tube amp but have been reading about them for years. I would like a classic tube integrated (or maybe separates) to compliment my wonderful recently rebuilt Pioneer SA-8800 solid state integrated. My primary speakers are KEF 104aB - also pictured are my ESS Trans-liner II (which have a fabulous KEF B139 transmission line design and which I will likely sell soon). I love the Pioneer and would like to be switch between it and a tube unit as the mood strikes me. I know the KEF 104aB aren't efficient, landing somewhere around 84 or 85db sensitivity. Some say these KEFs perform best with SS power but I would still love to tip my toe into tubes. Do you think a 28 watt Fisher/Scott would do the trick? What about something EL84 based in the 17 wpc range? I live in an apartment with open living room/kitchen so I would describe the space as medium or medium/large in size. My taste in music spans the gamut and I listen to vinyl as well as stream via a tablet/Topping D90 DAC. So, 17wpc, 28wpc or more? How much tube power do you think I need for all purpose listening in a medium size space at reasonable polite but fun volume? The SS Pioneer (80wpc) rarely sees anything past 4 on a 10 dial. What do you think?

 

[Mdpaudio]

Those speakers like to be man handled (controlled) by the amp to get the best out of them. Tube amps in general don’t do that well. In addition to needing a lot more power than many popular tube amps they also like a high damping factor to control the speakers. SS amps have high damping factors and tubes don’t in general. With 20 watts you’ll only get about 97db max which is loud but not lease breaking loud. I love my tube amps but only with very efficient speakers that are easy to drive, that is not the 104! See if you can get an in home demo of the amp first.

 

[opnly bafld]

What do you think?

KEF specified a minimum of 15 watts, so I think any @20+ watt push/pull amplifier (6L6, EL34, KT88, etc) should do fine (if you are not running a night club).
High damping factors are overrated, it's easy to see why if you do the math.
If you want good/better bass add a couple of subwoofers.

 

[TriodeLuvr]

That's very low sensitivity. I think you'll be disappointed with any attempt to use those in a tube amp system unless the listening area is tiny. On the other hand, if you don't pay too much, you can buy used gear and recoup all or most of your investment if you decide to sell later. Your best chance to make this work would be a large amplifier like the HK Citation II, but it's too late in the game to find one at a good price unless you're really lucky. The smaller Dynaco ST-35 is a good bet for sound quality, but again, underpowered for those speakers.

Jack

 

[Dandy]

I ran my KEF104aB’s with a Dynaco stereo 20 quite happily for about five years in quite a small dining room. So think in terms of 20w per channel, ie a pair of 6L6s or EL34s for each channel, rather than EL84s.

 

[Lou G]

I don't have KEF 104ab speakers but I do have KEF Calindas which I purchased new in 1979. They are similar to the 104ab with the same T27 tweeter, a slightly different B200 woofer version with a larger magnet and lower Q, a similar 44 liter cabinet volume but in a taller, narrower, deeper configuration, the same BD139 passive radiator, and similar crossover topology. I originally drove them with a Luxman R-1070 but did try a Dynaco ST-70 back in the day. It was a big disappointment. With the Dynaco, the sound was dull and lifeless compared to the Luxman. Over the years the Luxman was replaced with SS integrated amps and finally SS separates. The best sound i have had with the Calindas has been with SS separate amps including a McCormack DNA 125 (125 wpc), a Belles 150A reference (125 wpc) and an Acurus A200 (200wpc).

 

[Benjib]

I don't have KEF 104ab speakers but I do have KEF Calindas which I purchased new in 1979. They are similar to the 104ab with the same T27 tweeter, a slightly different B200 woofer version with a larger magnet and lower Q, a similar 44 liter cabinet volume but in a taller, narrower, deeper configuration, the same BD139 passive radiator, and similar crossover topology. I originally drove them with a Luxman R-1070 but did try a Dynaco ST-70 back in the day. It was a big disappointment. With the Dynaco, the sound was dull and lifeless compared to the Luxman. Over the years the Luxman was replaced with SS integrated amps and finally SS separates. The best sound i have had with the Calindas has been with SS separate amps including a McCormack DNA 125 (125 wpc), a Belles 150A reference (125 wpc) and an Acurus A200 (200wpc).

Thank you for your thoughts, Lou. Yes they are very similar indeed. I am wondering if you are mixing up the small magnet B200 SP1014 for the big magnet B200 SP1039 found in the 104aB. The B200 SP1039 actually weights a tad bit more than the SP1054 found in the Calinda but as you note, SP1054 does differ in spec, with lower Q as well as higher power handling. I wonder how the magnets differ in their construction as the SP1054 is a slightly more powerful magnet (13.5k vs 12k gauss) while the total speaker is .28 kg lighter than the SP1039 (assuming the weight difference isn't found in the basket).

 

[opnly bafld]

I have owned KEF 103.2s (86? dB) and ATC SCM 11v2 (85 dB) and they both worked well for me with 20 watt tube amps in my living room that is open to other areas.

 

[Lou G]

@Benjib, Thank you for the info. I was assuming the SP1054 had a larger magnet because it is slightly more powerful. I was just trying to convey the similarities and differences between the two speakers. I actually auditioned both the Calinda and the 104ab back in 1979 when I purchased my Calindas. They have a very similar sonic signature.