Amperite RA-1

From a contemporary advertisement:

Amperite Ribbon Velocity Microphone

EVEN today, the quality of a good amplifier or transmitter built five years ago cannot be greatly improved. A good condenser or ribbon microphone, however, will greatly improve the quality of any installation. In fact, it is by far the easiest and cheapest way to noticeably improve any radio station or public address equipment. Ribbon microphones are, therefore, rapidly gaining their just popularity. The new Amperite Ribbon Microphone incorporates a number of novel and improved design features. The cavity resonance of the case is entirely eliminated by the properly designed screen construction which permits free path to the sound waves. The case is also heavy enough to withstand a great deal of abuse.

The pole pieces are machined and placed in such a way as to obtain the highest flux density in the gap. Although smaller in size, the magnets are more powerful than the larger ones used in former designs. This is made possible by the use of 35% Cobalt Steel. The ribbon is hand hammered to .0002-in.

The output of the microphone is approximately -90 dbs. and has a flat response from 60 to 10,000 cycles (1 db. difference).

Besides giving the most faithful conversion of sound to electrical energy, is excellent for the ribbon microphone eliminating acoustic feedback. This fact and its low selling price makes the new Amperite Velocity Microphone ideal for public address work.

In using an Amperite Velocity Microphone, one must be careful in trying to reproduce sound effects. A vacuum cleaner will not sound like a wind storm to the radio audience, it will sound like a vacuum cleaner!

From a contemporary Amperite leaflet

Frequency response, 42 to 10,000 Hz. (Maximum difference I db.)

Output: -90 dB

Output Impedance 50 and 200 ohm. Other values if requested.

Mechanical Characteristics. Highest Cobalt steel magnets, insuring extremely long life. Ribbon of specially treated aluminium alloy that can't be stretched or distorted out of shape. Not affected by temperature, pressure or humidity. Bronze and steel case provides complete shielding.

Model RA-1. Especially designed for public address. Gives minimum amount of acoustical feed back and best voice quality. Can also be used for music.

Model RAE. For studio use. Similar in construction to the regular model RA-I, has greater frequency range, and slightly higher output. Also includes laboratory grade transformer.

Standard Transformer: A laboratory made transformer with the very best grade of specially annealed Silicon Steel. Not to be confused with ordinary transformers. Can be used for public address or studio. Frequency 60 to 10.000 Hz (±1 dB)

Laboratory Transformer: Highest grade transformer obtainable. Grid windings 150,000 ohms. Nickel alloy core, frequency range 25 to 15.000 Hz (±1dB)

LIST PRICE RA-1 $25.00; RAE $35.00

The new Amperite Velocity Microphone is the easiest way to improve any public address or studio installation. Your audience will notice the improvement through clearer, more natural tone. When the sound man drops peas on the kettle drum., over the ordinary mike it sounds like rain. Over the Velocity mike it sounds like peas dropping on the kettle drum. Brings you face to face with the performer.

It's directional quality is a highly desirable one because it helps to reduce acoustical feedback and reverberations; also helps to eliminate undesirable noises. If any noise originates from a nearby source it is possible to eliminate it or reduce to a minimum by placing the microphone at 90 degrees from said source.

Coutant.Org on Amperite Microphones

We are unsure of the production dates for this model but its successor, the SR80H, was in use by 1937.