"No, it has to do with turn on transients from the power tubes. I believe it is the indirectly heated ones that have a slower voltage build up."
Rick
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Right. It takes more time for the filaments to heat up the actual cathode tube, sumthin' like that.
You can watch the difference, 5U4 filaments come up within a few seconds. A EZ-81/6CA4 takes about ten.
I would guess that a directly heated rectifier tube would be more noisy, it's probably why you see chokes in the PS after the said tube. (Well, most of the time.)
However, I did swap a 5Y3 for a 5V4 in a SE 6BQ5 amp. It made it worse, dunno about that other than it's a lame circuit from get go.....
I know folks collect tubes because they are rare, but that kind of money for rectifier tubes?
Must be nice to have money to burn like that.
I'll stick with television half-wave dampers, they do a pretty good job when you think about it.
And nobody wants to collect the damn things......