KT90's anyone using'em ?

[kevinkr]

The KT90 is a bit of an oddball, originally this tube was designed in the late 1980's in conjunction with David Manley of VTL fame. The first samples I ever saw in fact were VTL branded, laters ones were just plain EI. I ran them at up to 600V in UL with relatively "few" problems.

Note that the KT90 plate structure is borrowed from one of the big EI sweep tubes, they were quite open about this at the time, what else they borrowed I don't know. I do remember the screen grid voltage rating was not far removed from the plate rating.

Edit: I also seem to recall that the curves for this tube were not kinkless under certain conditions - I never encountered a problem with this, but allegedly this is not the most linear output tube in the class.

QC was a bit of a problem right from the get go, the most consistent ones I have ever seen were the ones built early on for VTL, the later ones were considerably less consistent. I did have one (VTL branded) literally explode in my hot rodded Citation II which scared the **** out of me!

I thought good KT90 sounded better in that amplifier than JJ KT88 or even vintage used GEC KT88. I think Trombone here on Diyaudio is still using KT90 in his modified Citation II which is based on my design. You might want to give him a ping for his opinion.

[binkt]

I am using the KT90 in a HK Citation with J McShane mods (triode)and have had fine reliability. I hav VTL and EH sets used interchangeability. Also, they are used as push-pull parallel triode into a RAM Labs RM-9 output transformer to attain 70W per amp in mono home built amps. I have experienced no problems with the early VTL labled tubes and the newest EH version sourced from the TUBE AUDIO website as burned in matched quads. Both amp sets run about 450V B+ at 50mills triode and screens connected thru 125 ohm resistors to the plate. These are used in audio reproduction (not specifically guitar amps)

[richwalters]

In a few days I'm getting delivery of some EH KT90's to put in my 4x p-pp Slaughter amp: a wind change from 6550 New Ed TungSols. When it comes to THD, I'm finding that Svet 6550C winged C types and these TungSols are also near identical performers in UL with 40% taps with 68R screen res, both versions can take 80mA quies on the plates at 450V without wilting. In comparison the 6550WE clear glass pellet getters is hopeless sod at 30W; that tube behaves more like a rowdy 6L6. The indications for best UL linearity, both tubes like hard screen drive.
Another good tube for low THD is the SED KT88 large S USA Svetlana; I believe nolonger in production, another legal brand confusion as that is also made in Russia only for the US market.

More anon

Richy
I will inform how I get on with EH KT90's.

[radiostar]

Hello guys and greetings from Serbia!

As I could remember all rumors about Ei KT 90, everything started with Mr Manley, who was in doubt to buy complete 211/VT-4C stock available at that time or to invest in new tube. He decided to start production of new audio output tube ...


EI ( Elektronska Industrija) Nis, was only one or maybe one of just a few tube factories in EU at that time, except Soviet Union.

Visually, KT90 by EI look a bit grotesque , because Serbian Glass Factory in Paracin, Serbia, EI supplier of bulbs, wasn’t interested too much to make new shape like KT88. So it looks like EL519, without plate cap and with funny, pretty thin plastic base, vacuum was made at the top of tube, not on the bottom like all real KT tubes were produced for decades.

The guys in EI used EL509/519 structure with slight modifications, but quality of each series differs too much. Some of them are really OK, even more that you could expect of so ugly tube. I had opportunity to match a lot of pairs and quads, there were batches with almost identical parameters, and some of them are still in use after more than 10 years!!!, but at the other side, few late batches were complete disaster, even some of tubes destroyed amplifiers in which they were used.

I still have few quads of different batches, but I need to try to find them (among 20000 tubes ) and to suggest proper batches, if it’s possible to find them nowadays.

Good luck with EI KT90, because it’s lottery!!!

[Zen Mod]

Originally Posted by radiostar

Hello guys and greetings from Serbia! ......

I have nothing to add , besides that I' bored writing same things in last several years , on R.A.T. , Geek's and here .....

destiny of EI RC ..... shame .....

anyway - I just wanna say hello to you , and I'm glad that you have now your own site , not hosted on free servers as before .....

feel free to click on forum addy , written in my sig

[richwalters]

I agree: old subject :Ei KT90's were fit for clay pigeons.(or rather glass pigeons).

[Ty_Bower]

Originally Posted by radiostar

Visually, KT90 by EI look a bit grotesque , because Serbian Glass Factory in Paracin, Serbia, EI supplier of bulbs, wasn’t interested too much to make new shape like KT88. So it looks like EL519, without plate cap and with funny, pretty thin plastic base, vacuum was made at the top of tube, not on the bottom like all real KT tubes were produced for decades.

The guys in EI used EL509/519 structure with slight modifications, but quality of each series differs too much. Some of them are really OK, even more that you could expect of so ugly tube.

Grotesque? Ugly? I actually rather like the look of them...


http://i69.photobucket.com/albums/i4...E/P1120152.jpg

[taj]

Ty,

I love the way the chassis woodwork complements the architecture in your home.

..Todd

[Ty_Bower]

Originally Posted by taj

I love the way the chassis woodwork complements the architecture in your home.

Thank you. We call that style, "unfinished."

[rknize]

I'm not sure how these relate to the EH KT90s. They are similar in design with a tall, narrow envelope, but they were evacuated from the bottom. The plates are huge and they can take all the current I can throw at them. They sound pretty good in the Simple SE at 100mA...one of my favorites in there.