In-car C2 radio adjustment?

[Timothy B.]

I noticed when I had my radio out of my 67 C2 that under the turning knob there is a small screw adjustment positioned such that it just lines up with the hole created when the knob trim plastic piece is removed from the dash. Could this be an antenna tuning adjustment? If they went to the trouble of placing so that one could adjust it with the radio in the car, there must be a procedure for that? I just go my radio back from Dr. Don's for service and they said they adjusted the radio to a "standard" antenna and that no further adjustment is required. I am just curious as to the purpose of the trimmer in case it might need some tweaking for my particular antenna (assuming that's what it is for).

[Joe C.]

Re: In-car C2 radio adjustment?

Antenna trimmer for AM reception. Tune to a weak station near 1400 khz. Turn the trimmer screw for max volume.

[Jack H.]

Re: In-car C2 radio adjustment?

Corvette always put the radio antenna on the REAR of the car to keep it AWAY from engine compartment noise. This makes the antenna lead-in cable LONG and cable length dictates parasitic capacitance.

The trimmer adjust (a part of ALL radios of that era) is there to fine tune the radio's front end, signal detector, to your specific antenna. This shouldn't be a surprise because the t******* function is called out in the AIM (Assembly Instruction Manual) as well as the Chassis Service Manual and in all of the Delco Radio repair manuals from the era.

Others have described the process (tune to a weak AM signal at the top of the dial and tweak the adjuster to PEAK signal strength). This is a esoteric adjustment that will only be noticed while you're listening to AM signals, traveling in the 'boondocks' under fringe reception conditions. In major metro areas where received signal strength is strong, there's no observable effect from being a tad off center with your antenna matching impedance adjust.