100 ohms Hum Balance pot

[Carlosraj]

Hi


I did a modification of this pot for a Fender Twin because the pot was damaged. I connected two 50ohms 1/2W resistors to each side of the filament terminals to ground. It worked OK for a while without any hum but then the 2 resistors burnt out. Do I need to put in higher power rated resistors or can I do away with this 100ohm pot, if the amplifier doesn't hum.


Thanks

 

[Enzo]

Um, you cannot have both resistors AND the hum pot at the same time.

We generally use 100 ohm resistors rather than 50 ohms. But the point is that there is not usually any ground current. Your pot or the two resistors are in series across the 6v. SO whatever current that draws. A pair of 100 ohm dissipates about 2/10 of a watt. If you use a 100 ohm pot - same as two 50 ohm resistors, then it dissipates 4/10 of a watt.

 

[PRR]

> the 2 resistors burnt out.

How?? I assume this is a common 6.3VAC heater circuit. Then each resistor gets 3.15V. 3.15V in 50 Ohms is indeed 0.2 Watts, and a 1/2W should last "forever".

Something else is wrong. One possible is a heater shorted to other tube electrode.

You "can" have both pot and fix resistors. It's pointless and wasteful, but it won't burn.