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from another thread: what does putting the CT for the filaments to the top of the cathode resistor do?
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It is a simple way, without any extra components, to elevate the heaters by a DC offset. Whatever the cathode voltage is, will be how much above ground the heaters sit. This helps reduce hum.Education is what you're left with after you have forgotten what you have learned. -
Yup, what Enzo said....Comment
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thanks boys.
my tranny has a fillement center tap. so i should use it. correct?Comment
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If your running filaments on ac power, then I believe the answer is yes. The bias obtained off the cathode resistor is a light suppression. On the data sheets, most filaments can be offset by as much as 100 volts. Care must be employed if offsetting the filaments on a cathode follower circuit when that cathode is already offset by the 100K tail resistor.Originally posted by scole View Post
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IMO if your doing a 5E3 there really isn't a bunch of difference from CT to ground and the elevation method Audibily. Now in other amps and other situations it very well could be as long as you don't exceed the heater to Cathode voltage differential on the spec sheets as Gary mentioned. 70 volts works pretty good but if you want to do it sure it can't really hurt anything. Maybe try it with or without. One thing it doesn't do is isolate the output tube from the tranny but that's not that big a deal either. Gary have you ever tried using a diode from Cathode to Filament in the Cathode Follower example you mentioned ?Just wondering as I've seen it but hadn't tried it.KBComment
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Yes, use it.... but I also use a 47 to 100 ohm, 1/2 watt resistor on the center tap lead if connected it to the cathode biasing resistor.
I'm not sure if there is any real proof of this... but I think it feels a little safer in case the power tube's plate lug #3 accidently shorts to the filament supply lug #2.
I think the 1/2 watt resistor will act a bit like a fuse to the B+ rail.Comment
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