Audio Research Vs115

Paradigm Sig. 8 v3. I've had a devil of a time getting reliable and timely info about the specs, but finally got through. The S8s have a 21-22 max ohm peak between 1K and 2K Hz; and a 4 ohm min. in the bass region. I've been in private contact with one of our tech members and he did some math calcs that indicate the VS-115 should be able to drive the S8s with a relatively flat output response because the amp's output impedance is low for a tube amp. Soundstage and Stereophile bench tested the VS-115 and Ref 150 and they share similar electrical attributes re: NF (about 12-13), DF (about 7 or 8) and output impedance (approx. 1.1 ohms off 8 ohm tap; about half that off the 4 ohm tap). Based on his calcs, FR may be off +/- .5 db at the peak, which ain't so bad.

VS-115 maintenance tip. Just replaced the four 6H30 cathode follower tubes. May have run them out to almost 4000 hours. BIG, BIG difference. The amp definitely sounds better: tighter bass, more transparent, and so forth. I think in the future I will switch out the 6H30s before they have 3000 hours of use.

Any recommendations for new tube set other than the Audio
Research Brand. Can I use any 100 ohm 1 watt bias resistor
or need to order one from A. R. ? Thanks, Gerald
Have the VS 115

Gerald, for some reason ARC recommends using their parts, e.g., bias resisters. I don't know why. They only charge a buck so per resister. Selling "matched" resisters can't be a big profit center. So, I would order the resisters from ARC.

As to tubes ... I think the main stream brand is Tung Sol KT-120s, but there may be other KT-120 manufacturers. ARC charges about $100 a tube, which is twice as much as what other reputable vendors, such as Upscale Audio and so forth. I've gone both ways with tubes. I don't think ARC's KT-120s sound better than anyone else's KT-120s.

But there are two advantages going with ARC. One ... it has been my experience that ARC does a better job of matching tubes. An ARC matched pair biases very closely.

Two, if a tube arcs within 90 days of purchase, I believe ARC will replace it. They may also repair any damage caused, e.g., open bias resister. I'd check the last point.

Btw, I used to own the VS-115. Traded up for a Ref 150. I think the VS-115 is a super-duper amp. Enjoy.

Bruce

ARC recommends using their parts especially when it comes to the resistors around the output tube circuit because they are flameproof wirewound resistors. These parts are used to minimize circuit board damage when an output tube arcs. Instead of using a plain wirewound resistor where the resistor might heat up and scorch the board, a flameproof resistor basically pops and opens thereby minimizing damage.