Shieldplate Tube Corp.
208 South La Salle Street, Chicago, Illinois

This company apparently made only one tube - the SP122. It is a scren grid tetrode.

This article was in "Radio Engineering" for December 1927:

"The Shield Plate Tube corporation, 206 South La salle Street, Chicago Illinois announce a new four element tube known as the SP122. This tube employs a screen grid which entirely surrounds the plate of the tube, both inside and outside. This grid acts as a shield between the plate and the control grid, thereby reducing the capacity between the two elements to a negligible quantity."

"Due to this arrangement the tube has an amplification factor of 175, it is stated."

"The tube is desgned primarily for use as a radio frequency amplifier but can also be used as a detector or an audio frequency amplifier, with a few changes to the circuit connections."

"The filament voltage of this tube is 3.8 volts and the filament consumption is .133 ampere. Due to the low filament consumption it can be operated from dry cells or if desirable, a 6 volt storage battery, by using a 15 ohm fixed resistance in series with the negative filment lead."

"Much greater amplification can be obtained from this tube in both radio and audio frequency circuits".