Actually the story of KT90 is a bit different and as per my Serbian sources they've not been made for Telefunken. Rather they have been developed and commissioned to be developed for Manley Labs at the beginning of 90's which had an exclusive rights for distribution and sales of this particular model...
Post from Eve Manley which I actually found in a thread here on WBF:
"I was there at the factory twice in in January 1990, mid 1991, and DM went a third time without me.
I was first in Nis the first week of January 1990 where they showed us the first prototypes of the KT90. There had been some correspondence between DM and the Ei factory for almost a year before our visit as to what he wanted them to build. (See my post above regarding the KT90 NOT being based on the EL519.)
The actual engineering of the guts of tube was done primarily by the head Ei engineer, Blagomir Bukumira. We took home four samples and did the initial testing. Some suggestions were made and production began. This was the first "red" paint version. As with any first production run, of which we had to buy ALL of them, there were things to be improved upon.
The second version incorporated some structural modification suggestions from Bill Perkins. This was the "blue" version. You can see the additional spot welds for the concentric inner anode structure if you compare them. More meat. As I have previously posted, in 1993, tubes that fell outside our acceptable parameters were sold to a certain tube vendor who put on a prettier brown base and silk-screened their own "KT99" logo onto the glass.
Then the war started and the embargo went up and none of us could get tubes out of there. The factory also was having trouble getting raw materials IN. Contrary to rumors at the time, the Ei factory was NOT bombed, as we now know.
There later came a third version with wings outside the anode structure but gone was the additional inner plate structure needing all those spot welds.
The latest KT90's I have here, what I would call the 4th version, the sacrificial element tacked onto the anode structure that was square is now circular. Other than that, it looks like the version 3 tubes to my eye.
Here are some quick pictures I just put up for you.
KT90's I have known and loved...
As for bad blood, there was some disappointment as we were supposed to be the world exclusive distributors for the KT90 but this part of the contract was not ultimately honored by the factory, although it was basically more or less enforced for two years. It was the "less" part of this equation that raised some concern. On the other side, it was understandable that other tube amp manufacturers were not happy to have to buy their tubes from a competitor in the tube amps biz who had been granted "exclusive rights for the whole world concerning advertising, sampling, and sale."
I have faxes from Ei-RC from March 1991 outlining all of this. It is quite interesting stuff.
With this, with the war, with all the weirdness that went down, perhaps the factory's memories fall short in some areas, but I was there and I have the original correspondence needed to refresh my memories.
Cheers, Eve Anna Manley, Manley Labs"
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