Presently there are only two manufacturers of KT66 tubes in current production.  Those manufactures are JJ and the Russian brands owned by New Sensor that are all made in the same factory in Russia.  Since the war started, the Russian tubes became impossible to get in quantity and the prices went way up.  That leaves JJ and while those are nice sounding tubes, I can't get enough of them when I need them and have had a higher rate of defects in those than I like.

Our inventory of the Russian KT66 has run out so they no longer appear in our catalog.  The only amplifier specifically built for those tubes is our Zen Mystery Amp.  In January of this year we updated the bias window of the ZMA to work with KT88 and that amplifier now ships with KT88.  By shifting the bias window the amp is no longer ideal with most EL34 tubes.  Not that they were the ultimate in the original, but it would play them reasonably well.

There are more exotic KT88 tubes available in current production and by more manufactures than I can even try.  I think it is a massive upgrade to the ZMA because of the availability of all these different KT88 tubes.

With the KT66, once you've tried JJ and then figured out that all the Russian ones are essentially the same tube, it only leaves New Old Stock KT66 which run between $800 ~ $1600 a quad.   Takes the fun right out of tube rolling.

Here are some examples of different KT88's in current production that are not sanctioned due to war:





















KT88 will also work in the SE34I.6 and both TORII amplifiers, although both of those designs were targeted to EL34 and 6L6 tubes and will likely have better performance with those if you're looking for max power.  Especially now that we have the Decware EL34 that I'm happy to say is built better than the Russian Svetlana and Winged "C" tubes we started out with.

Also, this is not to say you can't find Russian KT88's or even KT66's.  You'll just pay a lot for them, but it should be no problem to find a quad or a couple pair at a time.  For me I have to buy in quantity and the tubes just aren't there and neither is the price.

Steve