Simple SE - Ei KT90?

[rknize]

Originally posted by Ty_Bower
I couldn't wait... I just stuck them in without making any changes. These are some seriously nice tubes. If you happen across a couple, give 'em a try.

I ran the EH KT90s at close to 100mA using the 340 ohm cathode resistor setting. They didn't seem to break a sweat and they sounded great. Not sure how the Ei's compare, but the EH's have a lot of extra fins on the plates. Using the same cathode resistor, the New Sensor 6550 (Tung-Sol) also flowed about 100mA with no trouble and sounded pretty good. That same setup on the SED KT88 caused a small amount of plate glow to form at the base of the fins. I run those at 390 ohms which I think puts me in the 80mA territory.

[Ty_Bower]

I'm guessing with the 810 ohms resistance I have right now I'm about 50~60 mA. You've got an Edcor power transformer, right? When I used to run KT88 with 560 ohms my Hammond got reasonably hot. I added an extra 250 in series to make the 810 I have now. My twenty watt tubes didn't like the lower ohms. That extra resistor could be easily jumpered out, which I should probably do for the big tubes. Maybe it's time to put a switch on the front.

I'd like to get the bias up a bit on these guys. I'd think it would put them in an even better region of the curve.

[rknize]

Originally posted by Ty_Bower
You've got an Edcor power transformer, right?

Yes, I have the XPWR035 which is rated at 200mA on the 740VAC winding. It seems to be fairly conservative. I've run it for hours at 100mA per output tube plus a bit more for the input tubes and it runs fairly cool.

I think those KT90s are asking for more, but they will live forever at those currents.