An interesting side note here......
I looked till my eyes were blurry at the Nostalgia Air schematic I posted in post #2, looking for the tone control and couldn't find it
Come to find out, that schematic only covered the 7H822 and not the 7H822-Z. So of course, when I did find the "changes" page regarding the -Z variant, sure enough there is the tone control (lower RH side of the page)
Disregard the one error in the revised drawing; they show the Grid & Cathode tied together, this is wrong, the cathode is grounded in the -Z model just as it is in the 7H822 and is NOT (absolutely couldn't be) connected to the control grid as the mistake shows it to be ....
http://www.nostalgiaair.org/PagesByM...0/M0025310.pdf
You have my apology if the original schematic I found, and not the updated one, caused you any uncertainty as to what the "mystery" control is.....