KY-1 Voice Encryptor

The TSEC/KY-1 was an  all tube,  50 KHz  voice encryptor circa 1959 .  The key generator was an nightmare to adjust. It was controlled
by a key card, just like the KY-3. Because it was a 50 KHz wide band device, it was restricted for local use to post, camp or stations and hardened sites.

John Heimer  was a USAF Electronic Communications and Cryptographic Equipment Technician (306X0) from 1960-1983, and was trained on many of the systems highlighed, in this web page, including the KY-1.

"I entered Crypto training at Lackland AFB on January 4th, 1961 (class 010461), which was a secure voice encryption system (Ciphony) class - KY-1 and KO-6.  Due to a USAF needs decision, I only trained on the KY-1 before my class converted to another system (KW-26).  After school, I was assigned to an Air Force Security Service unit (6922 RGM) on Okinawa in October, 1961, where I was one of two individuals trained on the KY-1.

As stated in your KY-1 summary line , it was tube-based, 50 KHz wideband device, and as it turned out, a not so secure voice encryption system  It was a three combination, military grey safe that contained the key generator, power supply, digitizing voice preparation components-everything except the push -to-talk handset which sat on top.  The push-to-talk function annoyed most users, because it was difficult to interrupt conversations.

The equipment (in our case) was located  in the Commander’s office.  Other than the daily key card changes and periodic preventive maintenance, there should have been little reason to ever see the unit.

The internal electronics was very voltage sensitive, and the unit would alarm out whenever the input power became even slightly unstable.  To ensure stable internal power, a somewhat complicated power supply was in place, which included a small servo device that reacted to the most minor input voltage fluctuations; the servo was connected to a potentiometer to maintain voltage levels.  That servo was a major problem in that it would hang up, resulting in an alarm condition.  This happened at least once a week, with the “fix” being to tap the servo with a rubber mallet, which caused it to release and stabilize.  The KY-1 equipment was a design that was not  thought out properly.

In reference to the security of the system, sometime in early 1962, it was discovered that red (clear voice) would be transmitted in the event of a specific tube failure in the MOD2 adder circuitry and the system was immediately removed from world-wide service around the May/June time frame of 1962, and I never saw it again".

Does anyone have a photo of the KY-1? Contact:


1) George Mace  <gmace8(at)>
2) John Heifer <johnandmari64(at)>

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Oct 13/18