It occurs to me that I should perhaps add some clarification to Matthias' statement I referred to just above, which I quoted in my first post of yesterday. That statement was:
If an EML 300B XLS is the right choice we have 1.5A heater current at 5V. There is no voltage regulation. A transformer a rectifier bridge and a CLC only. May be the XLS is underheated (so I hope) ore all other (right) 300B are overheated, because they draw 1.2A (some russians and chinese 1.25A)only. This would result a heater voltage above 5V...not so good for any 300B and very bad for an Elrog 300B, because the use of thoriated tungsten for filaments. Higher heater voltage will result a (much) higher anode current and a much lower lifetime...
What he is saying is that if the power transformer's filament winding is designed to provide exactly 5 volts to a 300B which draws 1.5 amps, if a different 300B which draws 1.2 amps is substituted the voltage applied to that 300B will be higher than 5 volts, to a degree that might be harmful over time. The reason for that increase in voltage is that the reduced current draw will result in a reduction in the voltage that is dropped across the resistance of the filament winding.
Note also that he is referring to a difference in current draw of only 0.3 amps.
In principle similar considerations may come into play when a rectifier rated at 2 amps is substituted for one rated at 3 amps. However I suspect that the sensitivity to filament voltage increases of the rectifiers being discussed is considerably less than the corresponding sensitivity of a 300B.
Best regards,
-- Al