Original 1176 F (what is this?)

[furn1979]

Hi. I'm in the process of restoring my (somewhat modified) 1176 (rev F) to its original state.

I came across this part, located near the Output section, which I don't know anything about... it doesn't seem to appear on any schematics.
https://dl.dropboxusercontent.com/u/2698650/IMG_0740.JPG

It's hooked up between the ground and C10/R30/Q5 base

304 would mean a 300nF cap, but there's a screw on it... vari-cap? What would be the use of this? Did the units come stock with this or is it likely a mod?

Thanks!

EDIT: added info

 

[gridcurrent]

It's hooked up between the ground and C10/R30/Q5 base
304 would mean a 300nF cap, but there's a screw on it... vari-cap? What would be the use of this? Did the units come stock with this or is it likely a mod?

The part marked 304 is a 30 series Arco variable trimmer capacitor.
http://www.rf-microwave.com/datasheets/1470_ARCO_462_01.pdf
Definitely a modification.
Seen on some ex Canadian Broadcasting Corporation 1176's.

 

[furn1979]

The part marked 304 is a 30 series Arco variable trimmer capacitor.
http://www.rf-microwave.com/datasheets/1470_ARCO_462_01.pdf
Definitely a modification.
Seen on some ex Canadian Broadcasting Corporation 1176's.

YES!
My machine is indeed an ex-CBC 1176. Is there a list of specific mods these machine went through? I found a few myself but I might have missed some too...

What was the use of this cap? Could it explain the lingering oscillation problem my unit has when I push the output gain real high?

EDIT: added a question