6550 tubes?

I was wondering what kind of tubes these are, what type of music they are for etc. I have had my amp for a while and it was modded and came with these tubes in it. It is kind of a stupid ? but I have been curious for a long time. The reason I want to know what sound they are for is I don't get to play regular mesas with 6L6 in them. Just a curious ?. THanks for the help.

sorry here are the pics
http://photobucket.com/albums/e384/dualrec221/?action=view&current=IMG_0995.jpg

hmmmmmm .......

Gosh, I would think you would need the bias properly set for these tubes and maybe the previous owner did this.

6550s are powerful power stage tubes. I think (someone may correct me) the US JCM800 Marshall uses these tubes. But many of these Marshall amp users had their bias set to use EL34s.

Stay clean even at high volume, they're hard to push (distort). If you like more preamp distortion than power stage distortions, then these tubes will do the trick.

Again someone may correct me but I think the legendary Ampeg SVT uses these tubes as well as estoric hi fi tube powe amps.

I'm surprise no one has replied back that knows more about these power stage tubes.

That's all I know about them and hope I bump this post up so other could reply.

Thanks finally for someone replying. Iread that diezels use them as well or something like that. The ? made me feel kind of stupid asking. I have had my amp for a long time, and I looked when I got it, couldn't find much. Thanks for the review though.

RR is more or less on the money...the 6550 is a higher-powered variation on the 6L6GC theme. It generally requires a bias adjustment, somtimes other minor mods are required to generate proper voltage when switching to these tubes. They are typically used in amplifiers in which very high headroom is desired-bass, hi-fi, and power-amps for rack folks, sometimes.

I think SVTs used a 7591(A?), as this was another waaaay high-powered 6L6 variant. Like many tubes, people with better ears and deeper pockets than I claim that modern models pale against original US units. They still don't command crazy Tele/Mullie money, however.

Yet.