Your Svetlana 6550C could be a Sovtek, if two years old or less, it almost certainly is.
In that case, swapping for Wing C 6550 or KT88 are both better sound in my opinion. Wing C is the tube that was called "Svetlana" three years ago.
The trademark name was lost somehow and causes confusion when discussing this topic.
Ole, the Penta KT88SC solid-plate version is getting lots of good comments on the Tube Asylum-- http://www.audioasylum.com/scripts/tv.pl?forum=tubes&s=U --you might Search and read a bunch. Those '88s are available here http://www.pentalaboratories.com/product.asp?dept%5Fid=5020&pf%5Fid=KT88SC+SHUGUANG but be sure you get the no-holes-in-plate versions.
I just bought a pair of ASL Hurricanes and that's what I'll be using.
I had a pair of Premier 12 monos for several years and after a bit of experimenting I concluded they sound best with the GE6550A they originally came with. Barring 2 quads of NOS black plate Tungsols dropping into your lap, my next choice would be the SED ("winged C") 6550C. (Svetlana 6550Cs have the 'S' logo, and are not the same as the SED.)
Rolling the driver tubes in the 12s can have as much impact as swapping the outputs. With the GE6550As, a single RCA triple mica black plate 5751 is a nice improvement over stock and RCA 6FQ7/6CG7 clear-tops also work really nice, or late 50s Sylvania 6CG7 are even nicer.
With the Mesa Baron amp that I had that had the option of using those two tube types. I don't know if the comparison would be the same in your amp. In the Mesa the 6550's (used 6 per side), gave the amp a warmer, "rounder" perhaps more "tube-like" sound. The KT88's (both types were the winged C variety, by the way) gave the amp more punch, especially in the low-end, and sounded a bit more clean and neutral in comparison...a bit less colored in that way. YMMV, as always. My preference, by the way, were for the 6550's in that application and with my system. I tend to prefer a warmer sound in general.
You might give the "reissued" Tungsol 6550's a try for about $40 a pop. I have heard nothing but good things about both their sound and their reliability.
Just this last year I bought a Music Reference RM-200 tube
amp. The amp came with two sets of KT-88, both RAM lab tested. While they sounded pretty decent, I had a feeling
I could do better. I bought a new quad of Tung Sol reissue
6550's.....OH MY GOD! I am now convinced I am DONE, the 6550's are just that good. It just seems everything is there, be it slam, liquidity, air, you name it. Maybe I just hit in the perfect match for the RM-200, but let me tell you the KT-88's are never going back in; they sounded congested and smeary when compared to the 6550's.
I could NOT be happier.
Your mileage may vary....but luckily I am getting 100mpg.
By the way, a "matched" quad of 6550's was $105!
I've heard so many good things about the reissue Tungsols that your post may have just pushed me over the top.
Where is the EH KT88 fit in here? My Zeus comes with stock EH,anything better out there?
My Cayin KT88 had originally Shungyang tubes. Good, but nothing special. I tried the Sovteks KT88s and they were lifeless and thin sounding. I tried the Electro Harmonix and they were a mediocre match, too much treble and not enough bass. The were very powerful though.
Then I got me the Tungsol 6550 reissues. They clearly outperform anything else, and this is what I am using. In triode mode for classical and ultralinear for Jazz and Rock music. I suppose they would be a good match for your amp as well.
Atomickid: where did you buy the Tungsols from?
Thanks! - the conclusion seems to be that 6550 is not less musical :-)
Maybe the idea (Jtimothya) to try tube rolling the 5751 and 6FQ7 is a better way...
For the time beeing I have JAN GE 5751 (new production I guess) and RCA 6FQ7 (Brasil, red color letters)
Comments on these driver tubes?
Here you go.....here is a current Ebay Buy-It-NOW from the seller I went thru :
4 Matched Tung-Sol 6550 Reissue tubes,NEW
Item number: 5855636196 Buy It Now price: US $103.38
Shipping is $6 bucks. I got mine in ONE day priority mail.
This guy (Jason) is VERY good...I have bought from him three or four times, very trustworthy, always prompt, good product.
Good Luck!....best money I ever spent. Hey, if you don't
want the 6550's, drop me a line & I'll take 'em as a backup.
My guess is you won't want to, tho!
This is my first thread on this forum though I have been lurking around for sometime now.
Psam, I too have the Cayin kt88 amp. Given that you have changed the output tubes so many times, how easy is it to bias the amplifier? I am planning to bias the amp over the coming weekend. Are there any issues you have faced when biasing? One doubt I had is that the biasing resistors are so close to each other. How and where do I connect the multimeter probes to the resistor?
I you (or anybody else) can help, that will be highly appreciated. Sorry for hijacking this post.