[hoppy08520]

After learning that KT120 tubes could work in the RM-9 in this post, I ordered a quad of Tung-Sol KT120's from RAM Tubes. I finally got a chance to try them out tonight and wanted to share some initial impressions. (I would have posted a followup in the earlier thread, but since the subject line refers to the RM-200, I thought I would add a separate thread to avoid throwing anyone off.)

Keep in mind that I've only listened to around three albums (plus a handful of familiar songs from other albums), so this is by no means an exhaustive review. If I can, I'll come back in a few weeks and try to post a followup.

So, without further ado, here is what I heard:

• The music sounded richer and creamier.
• I felt a sense of euphoria I hadn't heard before.
• In contrast with the Siemens EL34 tubes I had in the RM-9 earlier, the KT120s sounded less analytical and more "spacey" (not the best adjective) but not distorted or mushy. I wonder if this is the "tubey" sound that people use to describe certain amps and tubes.
• The best complement I can give the tubes is that I wanted to keep listening to one song and album after another.
• I'm not the type of audiophile who listens to a lot of equipment and tinkers with various tweaks and settings. So I generally don't gush about new gear. I wasn't really expecting to hear much of a difference because, so I was surprised at my reaction. I didn't really think I'd hear such a different sounds from different tubes in the same amp.
• I will grant that sometimes "different" sounds "better" at first, just because sometimes our brains like something that sounds different to break up the monotony. So, I will try to post back again later after the tubes sink in more.
• Per Roger's post, the four KT120 tubes put out 30 wpc each, for a total of 120 wpc. I sure didn't miss anything from the 220 (?) wpc that I had from 8 x EL34 tubes.

One thing I noticed is that after only a few hours, the tubes already have some flashing. In biasing the tubes, I turned the bias screw until the red LED adjuster lights just barely turn on, and then maybe half a quarter-turn (an eighth-turn) more. Is this normal?

For reference, I have a RM-9 MK2 that started out as a MK-1 until Roger upgraded it. I listen with the "medium" gain switch. The only tubes I've ever listened to it with are Siemens EL34.

Speakers: Spendor S100
Preamp: Anthem Pre 1
Cables: DH labs biwire cables

[rbwalt]

sounds like you do not have many hrs on the new tubes.correct?  if so give them more time to settle in. a total of about 50 to 100 hrs should be ok then sit down for some serious listening. let us know then how things sound.

[Ericus Rex]

I think Roger recommends biasing the amp with all 8 tubes in, then removing either the front or back row.  I think you may be biasing the tubes far too high with only the quad installed.  However, I tried biasing this way and found my bias too high after dropping to 1/2 the tubes (cherry plates after a while!).  So I got this...

http://www.amp-head.com/product_info.php?cPath=21&products_id=70


...and now know exactly where my tubes are biased.  You can get a cheaper version from Amp-Head and you probably can find them on ebay.  I recommend getting one soon; KT120s are too expensive to burn out prematurely!

[Roger A. Modjeski]

In response to Hoppy. Note that I was quoting dissipation not output power. The output power of the RM-9 with 4 KT-120s will still be over 100 watts. Output power is more a function of the amplifier than the tubes in it as long as those tubes are capable of supplying the current needed. The KT-120 can easily supply that current with half as many tubes.  In fact, an RM-9 with only 4 KT-88s will do almost the full power, its just harder on the tubes from a dissipation perspective. Since the KT-120 has twice the dissipation of most popular tubes one can use half as many in my amp (I wont speak for others).