by Bob Latino Fri Apr 22, 2011 12:19 pm
You "could" go higher on the bias on the KT120 tubes in the ST-120 but after careful listening - I don't find that the KT120's sound much better at higher bias levels. The amp will also run a little warmer if you increase the bias.
On the M-125 monoblocks, the use of the KT120 output tubes in place of the Gold Lion KT88's gave about an 8 % increase in power with just the tube change. You won't really notice the power increase IMHO.
The Tung-Sol KT120 tubes, in both the ST-120 and the M-125 monoblocks, sound a little "tubier" than the Gold Lion KT88 tubes with a little more mid-bass content.
Re: Triode/pentode switches. When you switch to the triode mode from the pentode/ultralinear mode the bias will drop very slightly and the amp will have only about 60% of the power of ultralinear. The amp will run a little cooler. Since you can make the switch from ultralinear to triode with the amp running, many audiophiles favor the ultralinear mode because the amp is louder in ultralinear. To really listen to both moder critically I suggest the following > Listen to a track in pentode ultralinear until the track is over. Make the switch to triode and raise the volume on your preamp up to a point that compensates for the loss of volume in triode. Now play the same track over again and decide which sounds best to you. Understand that your musical tastes, your speakers and other factors may favor one mode over the other.
Bob
