Valve Question - KT88 or 6550 ?

Folks - recent experiments with different pre-amps have enabled me to re-assess the Graaf 5050 power amp I acquired a few months ago. I am now rather glad I failed to sell it on...

Anyway, it takes 4 KT88 or 4 6550 valves. Are these just different labels for the same thing or are they different valves? looking at pictures on websites, they certainly look different.
If I tried KT88 instead, what differences might I notice? Is there any effect on power output?

 

KT88 was made by Mullard originally, whilst the 6550 is GE version.

So they have the same specifications, but do sound different. I find that KT88 tend towards emphasis of the midrange, highlighting vocals for instance, whilst 6550 tend to be punchier so can be better for rock/dance.

So having said that, I feel most power tube rolling is subtle when compared to the driver/splitter stage. People report 'fantastic' changes which are usually just new tubes vs old tired ones.

Having tried a few KT88 and 6550 I prefer ElectroHarmonics KT88EH or real Svetlana 6550C. Look here for details http://shop.store.yahoo.com/triodeel/6550kt88kt90.html

 

i think they are very similar electrically. different manufacturers tubes look a little different, but i think that's about the same as some 300b's having round (lightbulb like) shapes and others having a kink in the top of the envelope.

i think the kt90, kt88 and 6550 are all interchangable but have slightly different performance. i refer you to the below link...

http://tdsl.duncanamps.com/show.php?des=KT88

 

I swing towards the KT88. I originally used 6550s in my monoblocks, but I think the KT88 is a bit more of a ruthless valve - if you've got good amps, use them...but they can show up inferior electronics and circuit design. The difference can be more than subtle, I heard a much greater control, more detail, much more articulate bass, and it was generally more lifelike to my ears. I use JJ Electronics KT88s (push/pull).

 

sadly, I never had the chance to a/b 6550 vs kt88, they are interchangable, however, I think 6550 has a limit of around 550 volts, whearas kt88 goes upto 800 or so.

6550 is a yank valve, possibly came 1st not sure, then again, could be america's answer to the kt88.

6550 sounds deliciously laid back, airy, nice valve, may sound a bit too reticent, till you get used to it and realise how detailed it really is.Easy to listen to.

I don't think I have actually heard a valve I dislike anyway.

 

i tried GE 6550A's and EH KT-88's in my amp.

6550's sounded more "SS-like" - fast, great bass, extended treble, but the sound somewhat flat, cold and hard.

kt-88's are more "tube like" - warm, still very good bass, more lush, softer treble.