Posted by Dr. Toobz (A) on November 08, 2010 at 08:19:24

I'm an avid "Bottlehead" looking to build yet another integrated amp, something more powerful than my 6DN7 SET. As I live in a condo and have no woodworking or metalwork equipment, I have typically stuck with kits, as I cannot build an acceptable chassis for a pure DYI project.

The Elekit has caught my eye for multiple reasons, including the ability to roll different octal power tubes, clean layout, and plenty of reserve power for future use (i.e., when I buy a larger house). However, it's not a SET - and my only experience with tubes so far has been the SET topology. Thus, I'm wondering if I could get a few opinions? My speakers are 99dB/W/m Klipsch Heresy III's, corner-loaded in a smallish (11x12) bedroom I use as a den. Music is a mix of rock and jazz, on both LP's and CD.

The issue I have with SET's is that the bass is often mushy, the damping factor poor, and the frequency response somewhat peaky, no doubt the product of an interaction between the high Z-out and the rising and falling impedance curve of a complex load (in this case, 3-way speakers). I only use about a watt in typical listening, but 2W total isn't a lot of headroom for peaks (3dB, actually). I've figured that 8W would be about ideal for these speakers, giving more headroom that I'd ever need. I could build a 300B amp, but then again, I'd run into a lot of the same SET weaknesses. Thus, I wonder if a SEP amp like the Elekit might have better "slam" and a cleaner, less bloomy sound? From looking at the circuit, I'm a bit concerned about the output impedance being high, and the smallish OPT's not giving a ton of bass extension. Is this an issue in practice?

Also, I know that modifications are more or less not talked about by the kit developers, but has anybody tried the following? A) DPDT switch to cut the NFB, and b) second DPDT switch to tie the screen to the anode via a 100 ohm resistor for a pseudo-triode mode? These mods would let me have a whole range of choices in terms of tailoring the sound to the room and speakers, in addition to tube rolling. That way, if I found I didn't like the sound of the standard beam tetrode with NFB, I could loss a few watts and drop the overall THD by going triode (or conversely, add "bloom" by losing the global NFB loop).

Thanks in advance for any thoughts. At this point, it's either the Elekit or the Bottlehead Stereomour (2A3 tubes; 3.5W output), the latter of which I'm not completely sold on due to the AC filaments and previously-mentioned desire for at least 6dB more power in a future amp. FWIW, I do like a bit of second-harmonic distortion, so push-pull is out, and I've yet to find a reasonably-priced OTL that doesn't put out only 1.5W in single-ended mode or use those furnace-like 6C33C monster triodes.