Climate control systems in verticals

[Bill Spurlock, RPT]

I'm wondering if others have noticed temperature-caused pitch change occuring
while tuning verticals equipped with Dampp Chaser rods, and if so how you handle
it. It seems that because the heating rod is adjacent to the plate and strings,
there is enough warming of these parts to cause the pitch to rise or drop
several cents within about 15 minutes whenever the rod turns on or off.

While I have long suspected something like this was going on, one recent piano
really showed it clearly. It happened that when I first arrived, the heating rod
had been on for a while. Then about the time I started tuning, the humidistat
turned the 25 watt heating rod off. By the time I had finished the treble, the
middle and bass of the piano were around 4 cents sharper than I had put them. I
later tested a large upright in my shop by carefully measuring all the As and
Ds, then plugging in a 25 watt Dampp Chaser rod mounted in the usual position
inside the piano. Within 10 minutes the pitch of the bass and low tenor had
dropped 2 - 3 cents. After twenty minutes these areas had dropped 4-5 cents and
the low treble was also starting to drop. Unplugging the rod caused the pitch to
immediately begin rising again. Clearly the warming of the plate and strings
causes the pitch to drop, long before any drying effect of the soundboard could
cause such a change.

This would normally not be a problem during very dry times when the rod is
always off, or during humid times when it's always on. But when it happens to be
cycling on and off while you are trying to tune, it really messes up a tuning.
Dampp Chaser now has their new "Ultra" systems having most of the components on
the back side of the soundboard, under a mylar cover. These should solve this
problem, but are way more expensive. Has anyone found a way to deal with this
pitch drift problem while tuning? Unplug the system and adjust capstans for 15
minutes first?

Bill Spurlock