[Leadfeathers]

Greetings all -
   I'm a happy owner of an RM-9, currently using Tung-Sol 6550's.  Somewhile back a couple RM9 owners had mentioned they were using Penta Labs KT-88SC's (I think) and were very happy with them, but I can not find that thread; I think it was part of a different discussion.
   If anyone is willing, I'd like to hear their experience in the differences in sound output, tone, mid-range, bass etc between the 88's and the 6550's, once again, and which brand tubes might be preferred.  I enjoy immensely what I've got, but am always willing to consider the possibility of a change for the better; or a change just to try something new.
   My musical tastes tend to run to blues, classic jazz (quartets, small ensembles etc) where the midrange is usually the star, vocals and such. 
   Thanks in advance.   Great amp, great forum.
Jeff

[Ericus Rex]

I remember from a couple of years ago someone mentioning the Gold Lion KT66 was their favorite tube in this amp.  I have that tube in another amp and like it very much but unfortunately don't have an octet to try in my RM-9.  I've only tried EL34s and KT88s in my RM-9 and stuck with the KT88s.  Currently have Gold Lion.  Some on here rave about the Siemens EL34 available from Roger.  I've never been able to hear that tube.  But for my speakers, all the EL34's I've tried (in a few different amps) have given me a fairly flabby bass.  Of course, your mileage may vary and that problem may very well be with my speakers alone and have nothing to do with the tube itself.  Let us know what you've tried.

[rbwalt]

Ok here goes. i have had a RM9MK2 and now i have a RM9SE. I had NOS Siemens EL34's in the MK2 for 11yrs! I have the NOS Siemens EL34's in my SE now. It is the best overall tube for the amp. The 6550's are more powerful and are extended in the bass. They are slightly closed in the mids and are fuzzy in the highs. The KT88's are pushed in the mids. now if you have a speaker that has a hole in the mids then the 88's may be the ticket. For speakers i have the  Merlin VSM MXe's with Master RC's and Master Bam.The 34's offer the best balance giving some away in the bottom end. i have a very good bottom end. The JPS Kaptovator power cord and Cardas Clear speaker wire and interconnects may have a part in the over all picture along with the Joule Electra 150SE line stage. please feel free to check my system under rbwalt in the systems section. I hope this helps in helping one chose a proper tube for their amp and speakers.Just remember that the VSM's have one of the flatest frequency responses of any speaker out there which makes their overall balance superb and why they sound so dam good and right.This makes the 34's a great choice for them.

rob.

ps. happy tube hunting.BY the way get your tubes from roger.

[Ericus Rex]

There aren't many current home-audio designs using the 6550 tube.  It seems to have been relegated to guitar-amp status in favor of the KT88.  I don't know why exactly.  I briefly had a quad of Svets in another amp (they came with that used amp).  I didn't think they sounded particularly bad, I just preferred the KT88s.  Rob's description of their sound might be right.  I just don't remember too well.

Hey Rob!  Why don't you send me your octet of Siemens for me to take a listen?   

[rbwalt]

i believe that ken stevens at convergent audio uses the 6550's in his amps. some like them and some like the 88's. i still prefer the 34's for its over all balance. roger at music reference told me that the 34's were his favorite.i think it is important to stay with what the amp was designed with in terms of tubes. if you want to try different tubes please get tubes from someone who knows them inside and out and that are well matched. this is where ram labs comes in. roger wrote the book on tube testing and matching. to many buy tubes that are not well matched or tested. you get what you pay for.

hope this was some help to everyone.

rob.