[Hammarlund] HQ-100 Query

[Oliver J. Dragon]

Good Evening,

I attended a flea market recently and was looking over a Hammarlund HQ-100. 
I noticed that there was a small Hammarlund-type knob on the back panel 
with its shaft going from the inside rear towards the front (about 7 or 8 
inches or so in length. It rotated continuously in either direction and the 
front end of the shaft appeared to be located just below the clock, in the 
area of the antenna trimmer. It was too dark to really see through all 
those small ventilation holds that comprise the cabinet of the '100, and my 
poor eyesight didn't help matters. The setup didn't feel like 'factory' 
since the assembly wobbled a bit unlike the other controls. The owner did 
not have any info about it. I thought it odd that Hammarlund would have a 
control located on the rear of the rx but am not familiar with their equipment.
Is this a previous owner's mod or actual Hammarlund construction?
If a mod, any guess as to what it might be, assuming a QST or CQ mag 
modification article?
It was a nice receiver overall.

Thanks in advance for your input.
Ollie.