W7TI writes:

On Tue, 28 Oct 2003 18:38:39 -0600, Biz WDØHCO wrote:

Just wondering if I converted the 6.3 VAC filament voltage to a DC
voltage if doing so would be worth the effort to reduce hum.

Opinions ?

AC will work fine, but here's the key: Don't ground either side of
the 6.3 volt line. Many hum problems are caused by ground loops
where one side of the filament voltage is run through the chassis.
Manufacturers used to do this to save a few pennies by having only
one filament wire. In a mass production situation this can be made
to work, but for one-off design it's easier and better to just keep
the filament voltage isolated from the chassis or anything else.
Use a twisted pair and run it from socket to socket.

If I did this I would put a 0.01 uF capacitor to ground at each
filament pin, to keep RF from propegating through the wires. I would
also put a resistor to ground somewhere in the string to bleed off any
stray leakage current (maybe 1000 ohms or so), otherwise you might get
voltage buildup that could cause problems.

What about an inadvertent short between the cathode and filament?

Allen