Power Tube Sonics

[nc42acc]

All things being equal let's say you have a tube power amp capable of biasing numerous output tubes what are going to be the sonic signatures of each?
6L6GC, EL34, KT88, KT90, KT120, KT150.

[mep]

Of course it will be circuit dependent, but the 6L6 was never an output tube of choice for stereo amps as the KT-66 was much better. The EL-34 is known for a sweet midrange, but it can have really good bass in the right amp like the Quicksilver MS-190. The real Gold Lion KT-88 tubes were and are something very special from top to bottom. I never had much experience with the KT-90. The KT-120 is a very good sounding tube with good frequency extension, but the KT-150 is in another league and if it is possible to use it in your amp, I would highly recommend it.

[MylesBAstor]

Marty you are biting off a lot with that question. Too many variables: what brands, equipment, Chinese, Russian, NOS. NOC, OS, new, availability, etc? Whatsmore, what works in one unit, won't in another. But by far, the most important question is tube reliability. Personally, I've gotten past the NOS period and want to get the best new available tubes. All tubes are pretty much made in just a couple of places now: Russian, China and Czech Republic.

You would be better off focussing on one tube at a time or this thread will get real messy and no one will be able to follow it!

That said, I haven't heard anyone, audiophile or manufacturer, who doesn't think KT150 are one of the best pentodes ever built. Carl Marchisotto loves the KT150 in the ARC amps as does Mark. There are some real significant engineering feats embodied in the KT150s. However KT150s are not drop-in replacements for 6550s.

Among the 6550 class, the Russian winged SED are generally most people's choice but I don't think they are being made anymore. Hence the switch to KT120s. KT120s sound just fine in my ARTs and they should give longer tube life given the tubes are being run more conservatively now.

As far as KT77/EL34/KT88 tube types, the gold standard are real Gold Lions. The KT77 GL (original) sounded great in the Jadis and cj amps. Good luck finding them though. Great mids, limited at the extremes.

KT90s were originally made in the Ei factory in Yugoslavia and now look like are being made in Russia. They didn't see widespread use when new and IIRC EAR, VTL and Manley were their major customers?

[mep]

I don't know what happened to the SED 6550. SED makes some really good tubes. I still don't understand how SED lost the right to their original name Svetlana. Somehow their name was bought up and now Svetlana branded tubes are actually Sovtek.

[JCOConnell]

I used to have a Harman kardon citation II tube amp that used KT88 tubes. When I got it three of the tubes were weak and one of the tubes was bad on a tester so I replaced the entire set with Russian tubes and it sounded real good anyway. Funny part is I sold the original three weak gold lion KT88 tubes even described as weak for big bucks, more than I paid for the entire amp and tubes in the first place ( I did get a bargain on the amp ). I think this proves the point that certain brands and vintages of tubes can affect sound and are valuable for that reason.

[MylesBAstor]

I used to have a Harman kardon citation II tube amp that used KT88 tubes. When I got it three of the tubes were weak and one of the tubes was bad on a tester so I replaced the entire set with Russian tubes and it sounded real good anyway. Funny part is I sold the original three weak gold lion KT88 tubes even described as weak for big bucks, more than I paid for the entire amp and tubes in the first place ( I did get a bargain on the amp ). I think this proves the point that certain brands and vintages of tubes can affect sound and are valuable for that reason.

I used some real Gold Lion KT88s back in the '80s when I had my connie-j MV75A1s, interestingly Bill and Lew's first foray into the tube amplifier world. The GL were a H-U-G-E improvement over the commonly used GE 6550 (that people are paying bucks for today!). Much quieter, cleaner and open sounding, and pretty much better in every other way too. Could have never outfitted my present amps with GL though. 16 tubes is a bit much.

[GaryB]

I used to have a Harman kardon citation II tube amp that used KT88 tubes. When I got it three of the tubes were weak and one of the tubes was bad on a tester so I replaced the entire set with Russian tubes and it sounded real good anyway. Funny part is I sold the original three weak gold lion KT88 tubes even described as weak for big bucks, more than I paid for the entire amp and tubes in the first place ( I did get a bargain on the amp ). I think this proves the point that certain brands and vintages of tubes can affect sound and are valuable for that reason.

I have a restored HK Citation II that is switchable between pentode operation and triode mode. Reinforcing the comment made earlier that the circuit design affects the choice of tube, I find that even in the same amplifier, the mode of operation gives different preferences for the output tubes. The new Genalex Gold Lion KT88s, which are made in Russia, sound really good in pentode mode and are quite reasonably priced. In triode mode, I really like some NOS KT90s that I've got that date from before the war in Yugoslavia. The new KT90s aren't supposed to be as good but I haven't tried them myself.
---Gary