Great! Now I'm gettin it.
Time constant, doh, somebody spiked my corn flakes.
OK, 9 caps involved in driving that EL panel if you count the panel and the cap in the T4 that UA sells.
Sheesh. Someone was doing some tweaking.
That 47k/0.01 network does slope down from about 10k, which means less bass hitting the panel, which means less bass getting grabbed off the input signal.
Here is what the Spice Girls did to a simulation that did not include the tubes or their cathode resistors. The big dipper is with the R37 pot set for 1 Meg.
The blue line is with the pot off.
So pot set to 1 Meg = Bass Dip To EL Panel = More Bass at the output
Green Curve
Pot set to Zero Ohms = Blue Curve = Less Bass Dip = More Bass at the output:
So what the heck is that Red curve? It's caused by this trimmer cap on a later schematic. Set to 380 pf, it pulls down the graph a bit arounfd the 10K mark.(see above graph)
I thought I remebered something about a futile attempt to try and get the imaging to work better on stereo LA2 compressors by tweaking this cap, but I looked all through my old docs, and couldn't find anything. The trimmer does not do anything when the R37 pot is set to zero ohms.
FYI:
Here is a graph showing the pot turnned to both extremes, with and without the 47k/0.01 network.