[Ericus Rex]

It seems most tube amps can use a variety of power tubes - EL34, KT88, 6550, KT77, KT66, etc.  I've only ever tried EL34's in my amps but am curious about these other flavors.  What are the sonic generalities of these different tube types?

[Niteshade]

BIG Question! It's almost impossible to answer because the various flavors are 'extracted' from the circuit. Some circuits don't care what you put in them, others are quite particular. It also depends on the output transformers' qualities.

What are the tonal characteristics of your amplifier? How many watts is it rated for? Do you have to adjust the bias?

[Freo-1]

Not only what Blair said, but, the manufacture of a given tube type makes a big difference as well.

For example, a 6550 Tung Sol NOS (Black or Grey solid plate) sounds completely different than a Winged "C" 6550.   

[richidoo]

The circuit has a bigger influence than the tube, as do the signal tubes driving the power tubes. But given the same amp you might find that EL34 can be more ethereal, 3D, musically subtle. 6550/KT88 can be more meaty, hifi, better control, lower distortion. Music preference will determine which tube works best if you are lucky enough to run either.

A great designer like Roger Modjeski or William Johnson can make a 6550 almost as graceful and subtle as EL34, with double the power and control. The circuit is king.

[Ericus Rex]

Thanks guys!

I have two amps that runs these types of tubes: a Music Reference RM-9 (mk. 1), 100 watts/ch, fixed bias, and a Quicksilver GLA, 40 watts/ch cathode bias.  The RM-9 has lots of bass slam/attack while still having a lucious midrange - great all around amp for any type of music!  The GLA has much less bass slam/attack but is far more delicate sounding - truly excels at chamber music and small scale acoustic but doesn't do rock music extremely well.

I'm sure the circuit is extremely important in extracting those flavors.  I'm just looking for gross, even gratuitous, generalities.  All I've ever heard along these lines relates to the EL34 (lusher midrange) and KT88 (tighter bass).  I'm wondering where the other types fall in this blood line.  It's too expensive for me just to buy a few quartets to try (8 power tubes in the MR, 4 in the Quicksilver, both requiring matched quartets).  Any help is appreciated!

Oooooops!  I forgot to include the TRUE 6CA7 and the KT90!

[JimJ]

I'm just looking for gross, even gratuitous, generalities.

I don't think you're going to find them

I've heard KT88 amps I've liked, and EL34 ones I've liked...PP or SE...it's just so subjective it's hard to pin down.