RCA SK-45B

From EQ magazine, September 2000

PRICE WHEN NEW: $49.85 (in 1961)

YEAR OF MANUFACTURE: circa late 1950s

MIC NOTES: Designed to be visually less obtrusive than some of its contemporaries, RCA's SK-45B microphone was physically smaller and had simpler lines than mics such as the Type 77 or Type 44. It was intended essentially for talkback, cue, and public address purposes, where clean sight lines were becoming more of an issue with television broadcasts. Its sibling - the SK-45 - had a somewhat more limited frequency response of 80 to 8,000 Hz. The SK-45B's appearance is very similar to RCA's KN-1A and KN-1B microphones. The KN-models featured an integral desk stand with a compartment in the shank of the stand to hide the connecting cable's XLR connector, whereas the SK-45B could be mounted on any floor or desk stand with a standard 5/8-inch, 27-threaded fixture. The SK-45B was also identified by RCA as the MI-12045-B.

USER TIPS: The SK-45B is mounted on an adjustable swivel that may be moved through a range of 80 degrees (vertical). Impedance of the microphone could be set at either 200 Ohms for a balanced output of -56 dBm, or 15,000 Ohms for an unbalanced output level of -58 dBm. The SK-45B was originally supplied by RCA with an integral, unterminated 25 foot cable.

Technical description taken from RCA's 1959 Catalogue:

The Type SK-45B Announcer Microphone is suitable for talk-back or cue purposes. It may be used indoors or outdoors where a rugged, light weight microphone with good response to voice is required. It is a "close-talk" microphone. is This microphone is a pressure operated microphone employing the dynamic principle. The moving element is a thin moulded diaphragm in which a single straight wire embedded. This wire which is held in the air gap of a strong permanent magnet generates a small voltage of the same wave form as the sound acting on the diaphragm. The wire is connected to the primary of a small, but efficient transformer, in order to provide an output voltage sufficiently high to allow the output to be fed directly to the grid of the first input tube. The two conductor shielded cable is connected permanently to the microphone.

Directional Characteristics

• Below 3000 Hz: Non-directional
• Above 3000 Hz: Semi-directional

Output Impedance

• 150 to 200 ohms balanced, or 15,000 ohms

Output Level at 1000 Cycles/sec

• Low Impedance: –56 dB *
• GM: –47 dB *
• High Impedance: –58 dB *

Hum Pickup Level

• –106 dBm **

Frequency Range

• 70 to 12,000 cycles/sec

Mounting

• 5/8"–27 fixture thread

Dimensions

• Height (including shank): 5½"
• Width: 1⅞"
• Depth: 2"

Finish

• Low lustre grey enamel

Notes:

* Referred to 10 dynes per cm².

** Hum field 1 × 10⁻³ gauss.

0 dB = 1 volt.

A description of the related RCA KN-1B at the Coutant Website