Etherwave standard tuning issues?!

So, I have been actively practicing, but since I ran out of repertoire (I learned everything in this batch that I set out to learn) it has been about 5 days or so since I practiced last. My tuning was set to about 10:00, normally it is like 12:00, but I haven't been letting it acclimate (I know, but I just wanted to get into playing)... If I let it acclimate the tuning/pitch field is normal and stable. 

Anyway, I found some new repertoire and went to practice. I was very scared when I went to tune because the pitch field was so screwed up. I had to turn the knob ALL THE WAY TO 7:00 (can't move it anymore) and the pitch field was still VERY small. Zero beat was not quite even to the middle of the instrument!? 

I want to note, that it has been rainy over the last few days, and when the heat comes on it is very dry, which is okay if it is consistent. Though the temperature hasn't been consistent, and combined with the rain the basement feels very humid. I was playing music in the basement on Monday and it was very dry and normal, but now I smell a *bit* of mildew and it feels humid, which is weird because normally it is very dry. It has been raining all day. 

I am wondering if I should let it acclimate for a while, and see what happens, as that has expanded the pitch field in the past. Or what should I do? 

Should I open it up if it doesn't acclimate at all? I am a bit worried that something got screwed up so I don't want to mess anything up. I am using a Behringer K450FX amp and AFAIK, the power supply should be fine... ??? 

Is it the crazy weather? I have plans with other musicians soon, so I am a bit worried. Advice plz. 

Humidity can affect tuning, and if the wood case is exposed to sustained humidity it can absorb moisture over several days that can also take days to dry out.  If this shift came up rather suddenly and it has been in an environment of obvious humidity, I would give it a chance to dry out before jumping to any conclusions about pulling the cover and re-tuning.  If you can elevate the temperature in a small room like a tiled bathroom (but don't run a heater in a closet!) it will accelerate drying if stored there, but it may still take a few days.

If you do get the theremin in a stable environment for a few days and find that it isn't recovering, you may have to resort to retuning, but let's wait on that until the time comes.  Unfortunately some Etherwaves can require re-tuning eventually, and it's something that does require some patience and ability to track your steps. The Etherwave has a very wide pitch tuning range via the knob to accommodate these environmental and aging variations (which is also why the pitch knob is overly sensitive in normal operation), but sometimes the theremin needs a tweak to get the zero-beat re-centered.

I live in a climate that has a wide variation of humidity from winter to summer, and I've had to replace the pitch antenna on my Etherwave with a slightly shorter rod but with an additional short brass slider tube over the end that allows the length to be adjusted slightly longer or shorter than the stock antenna.  This then acts as a coarse tuning adjustment and can in many cases eliminate the need to go inside the case to retune the variable inductors.  The Subscope theremin (see top image at link) uses this coarse tuning method in conjunction with a much more manageable tuning range with the knob. If you have an antenna slider you can also make a simple optional modification to the Etherwave board that makes the pitch knob far less sensitive. 

But for now, dry it out and see what happens, and check back in with your progress.  And try to keep it in a stable temperature/humidty environment if at all possible.

Thank you for the reply! I hope you are right! I also want to note, that it appears, as I *attempted* to play some pieces that I know very well, to test, and it struck me, that even though I was able to get the pitch field to expand a bit, there seemed to have been a problem with the linearity too??!!! Because the whole time I kept having to make odd adjustments throughout registers that usually are not a thing, and when I tried to adapt to those adjustments... the distance b/t the same interval I just played in a mid range octave would just change on me again in the next phrase! *facepalm*  I didn't change my hand movement at all. 

Do you think this is just related to the fact that the tuning got screwed up and the field was just smaller than I thought so I was just instinctually standing closer to the instrument (more uncomfortable) to compensate, and therefore any slight movement would have made the pitch field shrink and created an illusion of poor linearity? I was able to expand it (not stable) to a point that *appeared* playable... HAHA. 

Is the pitch field just having a hard time stabilizing? 

OR is it possible that all the rain and dampness in the air also made the linearity a bit wacky? 

All I know is that I was pissed I couldn't play normally lmfao. 

Have you changed the position of the theremin or are there things nearby that weren't there before? The pitch antenna capacitance and thus tuning react sensitively here.

no, haven't changed anything

I also think the wooden housing has succeed up some moisture which causes the trouble. I built the EW from the kit, the wooden housing I painted at the outside and the inside (!) using hydrophobic synthetic resin varnish to prevent changes in tuning due to moisture. I was kind of surprised that the factory build EWs seem to be only varnished at the outside.