The oldest tone control or EQ?

[Viva-Tonal]

Here's something I've had since 1986, that I got off a retired radio/TV serviceman. It's a Radiart model JA. Apparently it had once been used with a vintage console radio he had (a 1929-vintage Sterling Troubadour). I had built an amplifier back then that used a number of early tubes, with a pair of 45s in push-pull for output. I used this unit successfully with it! (His radio used two 71-As but the pin-outs are the same.)









This unit was connected to a radio set by removing the two output tubes, inserting the tubes' pins through those two wafer-like devices, with the soldered sides facing up. The two leads would go from the plate of the one tube to the plate of the other.

Inside the box is a choke, a wire-wound pot and a capacitor. Full counterclockwise places the capacitor across the plates, filtering out the highs; midway seemed to take everything out of circuit; full clockwise places the choke across the plates, cutting the low end.

The leads are 3' long. Dimensions of the case: 4" wide, 3" high, 5 ⅛" deep (6" including knob).

[MordEth]

Thanks for sharing the photos and information about the tone control with us. I tried searching for further information about it, but Google was letting me down. Do you know approximately when this was manufactured?

— MordEth

[Viva-Tonal]

Not with any accuracy beyond by 1930, as the set he had was made in 1929. It couldn't have been made for too many years, between that it was designed as an add-on to sets that used the early 4 pin UX base output tubes (UX-210 aka 10, UX-250 aka 50, UX-171 and 171-A aka 71-A, UX-245 aka 45) which were introduced between c.1926 and 1929, and for sets without integral tone controls. Tone controls began to be included much more frequently in new sets after 1930 or so.

[gregbogantz]

Interesting bolt-on gizmo. That's the first one I've seen that offers both a treble cut and a bass cut. Most tone controls of this period were merely capacitors and rheostats that were placed between the plates of the output tubes so they offered only variable treble cut. The Victor 1929 sets had this type of control, but it was not meant for easy consumer use. It was located on the power amp chassis which was accessable only from the back of the cabinet. It was supposed to be adjusted by the installer of the radio set to match the room acoustics at the time of installation.