DC elevation of heaters

[wizard333]

What kind of noise reduction can you expect to see with this? Complete heater - cathode hum elimination? Marginal?

[EFK]

I implemented this and it works out that I've got DC in the mid-40V range on the filament CT. It works perfectly - in regards to what it accomplished, there is a very noticeable reduction in hum and it was quite easy to install. Not sure exactly where the heater hum was coming from but it was definitely heater hum and I would say this reduced it by a good 75%.

[Enzo]

Yes, it is effective against that particular source of hum. It would do nothing to help against hum such as might result from a grounding issue.

Hum can come from a number of places, and each source must be treated separately.

[wizard333]

Another couple questions............

1) If you are creating low V power supplies (rectified/filtered +/-3v) off your heaters and you elevate the heaters, what kind of havoc are you going to cause? Any clever way around that? Blocking caps before the rectifier for the low V supply? If so, suggested values? Since what you're wanting to let through is 3vac at (?) hz, you'd want to use a blocking cap large enough not to roll that off right? Or am I totally off base?

2) Any clever way to do this on a PT such as a Fender which doesn't have a CT for the heater lines?

[harry]

Are 1W sufficient or do I need to go higher? Any thoughts?

Well, P=V^2 / R

So re-arranging

R = 305 ^ 2 / 1

R = 93205 ohms

That would theoretically dissipate 1 watt, so for 1/2 a watt, make sure the total resistance of your divider is at least 180k. You'd still want to go higher to be on the safe side, I'd expect.