My experience with over 20 T-47, T-47A, and ATC units has most of the autotune knob locking plates having red triangles painted the to indicate, I think, an unlocked knob. The locking T bar is black.

Jeep K3HVG

On 02/25/2026 6:52 PM EST Hubert Miller <[email protected]> wrote:

I had never noticed the difference in color of the knobs on the ART-13.
Kinda reminds me of this puzzle in the local newspaper – “Find 6 differences in the drawings”

and the tendency is to overlook what’s “not important”.

So why the red knob skirts and some black ?

Photo via Julyah, pres of the PSARA antique radios club.

-Hue Miller

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