• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

For hk citation II owners\experts.

Hello, this is my first post on the tube forum; I am a kind of noob in electronics so i hope you'll excuse me for any inaccuracy and improper terminology. Here is my question:
I have purchased a couple quads of VTL\EI kt90 tubes and would like to try them on my HK citation II but I have no idea on how to bias them. The amp has been restored using the Mcshane power supply kit and the KT88 I am running now are biased at 85 mA each... Should I bias the KT90's at the same current
or more?
Thanks in advance for any useful and precious advice you will give me.
 
While I'm very familiar with the Citation II, I'm not too familiar with the KT90s. I think they are supposed to be a stronger (higher dissipation) version of the 88s. I would keep things at 85 mA because you must remember that the Citation II uses a voltage doubler. Doublers don't like to supply lots of current and the overall voltage will fall as more current is demanded. The power transformer will also run hotter then it already does. And heat is the enemy. But I'm a conservative.
 
While I'm very familiar with the Citation II, I'm not too familiar with the KT90s. I think they are supposed to be a stronger (higher dissipation) version of the 88s. I would keep things at 85 mA because you must remember that the Citation II uses a voltage doubler. Doublers don't like to supply lots of current and the overall voltage will fall as more current is demanded. The power transformer will also run hotter then it already does. And heat is the enemy. But I'm a conservative.
I will start from there (85 mA) and listen if the tubes sound allright I also think It'll be safe as far as I keep the same current as now. I'll also keep an eye (and a hand) on the power transf to check if it gets much hotter (gets already QUITE
hot bythe way, around 55 Celsius)