Valco speaker field coil windings

[MzunguSteve]

We'll be interested to hear the results of connecting it, and if possible, connecting it both ways (phases). I'd expect one way will introduce even more hum than what is there when it is not connected, but I'm only speculating.

Connecting the humbucker winding, in the same polarity as the coil on the Gretsch amp, reduced the underlying hum level (volume at zero), but there is still a smaller residual hum level.
I haven’t tried reversing polarity yet. I suppose temporarily shorting out the humbucker would give a clear indication of the level of hum reduction. Will report back tomorrow.
This has been a great experience for me, being able to benefit from shared knowledge.
It’s what I love about engineering.

[MzunguSteve]

We'll be interested to hear the results of connecting it, and if possible, connecting it both ways (phases). I'd expect one way will introduce even more hum than what is there when it is not connected, but I'm only speculating.

Interesting results.
Reversing the connections of the humbucker made a -5dB reduction in hum with valves warmed up and volume at zero.
Measurement was made directly across the voice coil with a Lindos measuring settings.

[g1]

So it reduces the hum either polarity, but one way more than the other?

[MzunguSteve]

So it reduces the hum either polarity, but one way more than the other?

Definitely. Reversing polarity reduced the hum level by 4dB, with volume at zero.
Before reversal the reduction was only 1dB.
Effectively the level is reduced to a third of what it would be without the humbucker.