Elrog 300B vs Takatsuki 300B tubes

Mk,
I haven't noticed that with my amplifier thus far. 
I thought I have another bad Elrog replacement tube a few days ago, no sound from one mono block. I removed it and use my EML,still no sound, uh oh. I had it check out by a friend who is an excellent tech. Turns out the recently installed cathode resistor had a bad solder joint. This was corrected and the Elrogs are working fine and sounding fabulous. 
Charles, 

May it be that the filaments of the Elrogs are very bright after switching on the amp for 2 or 3 seconds and then the brightnes is decreasing within the next about 5 to 10 seconds?

Brightness on turnon that slowly dies down is a sign of overvoltage on turnon and will quickly harm the filament.  This behavior happens in a number of 300B amps and the thoriated filaments light up much quicker making the behavior much easier to notice.

dave

Well, that bodes well for the end results of Charles' cathode resistor modification experiment, which was explicitly suggested to decrease a surge in voltage at power-up.  Hopefully that does indeed fix Elrog reliability problem... I guess we'll know in 6 months.

What I am referring to is the filament voltage at turnon and this has little to do with the value of the cathode resistor.  If the filament glows brighter at first and then settles down to "normal" it is being unduly stressed on turnon.  This goes for all directly heated tubes and it just so happens that the thoriated tubes make the situation much more visible due to their quick turnon.

dave