Tubes Asylum

Posted by Kico (A) on April 17, 2010 at 14:38:43

Thought you guys might be interested; this from Bob Latino over at the Dynaco Tube Forum...



At about 5 PM on 4/15/10 the Big Brown Truck dropped off a matched quad of the new Tung-Sol KT120 tubes. I pulled the Genalex Gold Lion KT88's out of my personal ST-120 and dropped the four KT120's in there. They biased up fine with no issues. The bias system on the ST-120 is set up for KT88's. These tubes biased pretty much in the same general area that the Gold Lion KT-88's did. According to the KT120 spec they draw about 1.7 to 1.9 amps heater current per tube. The two 6.3 volt AC lines on the ST-120 are rated at 5 amps each.

I let the amp warm up for 15 minutes without playing any music and then set the bias at 55 milliamps per tube. Later the bias was turned up to 65 milliamps per tube and then later to 75 milliamps per tube. IMHO these tubes sounded better as the bias went up. Most of the listening was done at 75 milliamps per tube. The rectifier was a WZ68 Weber Copper Cap and the three 12AT7 driver tubes were a Telefunken 12AT7 in the center position and two Mullard CV4024's in the two outboard postions. Although the ST-120 may be used in either triode or pentode mode, all listening with both sets of tubes was done in the pentode mode.

I listened for about 5 hours with various selections of acoustic jazz, vocals and some classic rock. This system consists of an OPPO BDP-83 Special Edition CD/SACD player, a BAT VK3i preamp, the Dynaco ST-120 power amp into a pair of Tyler Acoustics Linbrook II speakers.

Listening impressions ...

1. In general, the Tung-Sol KT120's seem to have a more "tubey" sound in this amp than the Genalex Gold Lion KT88 tubes that were in there.
2. The Genalex Gold Lion's have just a little more top end "air" than the Tung-Sol's..
3. The Tung-Sol's seem to have a more "full" sound with more mid-bass content than the Genalex tubes.
4. Both tubes seemed pretty much equal in soundstaging in both width and depth.

Other impressions ....

These tubes appear to work fine in the ST-120. At no time did the fuse blow or at no time were there any playing abnormalities. The transformers did not appear to get any hotter than when using KT88's in there but I honestly did not make any definitive measurements to verify that impression. With a retail price of over $70 each they are expensive but the Gold Lion's are $50 each so they are not cheap either. It is probably not fair to compare brand new tubes (KT120) with tubes that are well broken in (Gold Lion KT88's). These tubes will need more time on them and my impressions could change once they are broken in. I will probably give an update on the Tung-Sol's once these tubes have more time on them.

Bob

Fri Apr 16, 2010 4:19 pm

Regards,
"Kico"

||||||||||/
(@@)
_( . .)_Ooo__