Extendadot Speed Control
Below are two Vibroplex Deluxe Jeweled bearing speed keys equipped with the Extendadot Trombone speed control. One made of brass and the other made of stainless steel. It allows sliding the speed control weight beyond the end of the key by several inches in order to slow down the dots. For the really slow speeds it can have a weight at the both front and rear on the Nylon uprights. The front nylon upright tightens the trombone down on the dot arm. Anything you place on the dot arm has to be very secure or it will kill the dots. The full sized gold plated Vibroplex Presentation is on the left and the chrome plated Vibroplex blue racer is on the right. There weren't very many blue racer deluxe keys made and this one is from 1947. In order to use the Trombone speed control, all you do is slide it onto the dot arm and adjust the left and right stop screws for the slightly larger diameter of the dot arm. And attached is a youtube video I made of a 1906 Vibroplex Delux