Hum balance pot for s.e.x. 2.1

[Jim R.]

I've read a number of posts here that refer to some amps with a slight hum, and a 100 ohm resistor on the center tap of the heater supply. This makes me wonder if it would be possible/advisable to use a hum balance pot in the 2.1.

In the past I had a SE amp with a DC heater supply, but instead of being mounted on the top where the user could adjust it, it was internal, set, and then glued in. Place. Could something like this work for the 21, and what would be a good starting point for value and power rating? I'd see it more as a fine tuning adaptation instead. Of just guessing at a resistor value and hoping for the best.

Do the engineers out there think this is workable and/or advisable?

I should note that I'll be building my s.e.x on a somewhat larger top plate and will have some extra room to play with, so I won't be constrained by room and excess heat.

Thanks,

Jim

[Paul Joppa]

The 100-ohm resistors go to ground, one from each heater terminal. This drains the common-mode hum, which is caused by capacitive coupling between windings inside the transformer.

A hum pot would do the same, with an added possibility of minimizing hum caused by the residual hum of the DC supply, coupling to the cathode by leakage or capacitively. I can't recall anyone trying it, so I have no indication of whether that is a significant effect.

The hum pot will not compensate for residual ripple on the high voltage supply.

[Jim R.]

Paul,

Thanks. Got to give this one some more thought.

Thanks as usual,

Jim