kt88 vs kt150

Of course results will vary by amp - but I've tried all 3 in my VAC 200iQ auto-bias monoblocks. The KT150 sounds most different of the 3. KT88 and 120 are much more interchangeable. In my VACs the 150 indeed gave a far more powerful bottom end (certainly overdeveloped and overpowered), but it was "too much" and out of proportion to the rest of the music. Fun for a minute, but ultimately tiresome. Definitely not for me. I sold them. 

The Tung-Sol KT120 has a touch more powerful bass than KT88, without being overblown. Still a balanced musical tube while being particularly great for rock music IMO. Gold Lion KT88 has a more vibrant, rich midrange and more open top end - best for most musical genres other than hard rock & metal. In my case it's easy to see why GL KT88 was the manufacturer's stock choice, but I do still quite like KT120 on swap too. 

@lloydc similarly to what @mulveling shared here, I did the something comparable. Started with KT88s in one amp, then KT120s, and KT150s in two different amps. The past year I stored the KT150s and tried KT120s again - - but let them burn in at least 100hrs before making judgements too fast. Very nice at 200hrs+, liking them.

Previously like many others, I kind of overlooked KT120s and jumped to KT150s prematurely. Don’t get me wrong, KT150s are nice and can do well with the right input tubes, and caps, and cables for the amp - - however, once the KT120s finally settled in they offered the balance between the two mentioned by mulveling above.

Re-discovered KT120s again lurking back over a whole bunch of old Conrad Johnson threads. Some of the CJ amp guys were diehards about 120s. I see/hear more now.

I liked the KT120s well enough recently picked up another quad just to have them as spares if that helps add confidence. The "balanced" word mentioned comes to mind for me too. They are still nice, rich, but not spiking in any area imo. And, there are some who rave about new-repro GLKT88s, had those before, they are nice too!

As stated above, it will depend on your amp and system. KT150s definitely sound better in my Zesto Bia Select 200.

With that said, I've found KT150s to be unreliable. I've had to replace two in less than 250 hours.

Thanks for the insights!  Guess I’ll have to experiment.