Corsair II Relay Noise Mod

From the Ten-Tec Reflector November 10, 2000

Gentlemen :

After two months as a CII owner, I finally decided to try my hand at CW operation; having heard such marvelous reports of the CII being the consumate world class CW rig ….

So I plug in my trusty J-38 and start terrorizing the 40 meter novice band…

And am greeted with this miserable raccous clacking and clucking after each line of code.

It sounded like a dying chicken inside the radio …

Turns out that all the noise was coming from relay K1 on control board 80978.

K1 is used for activating a linear amplifier.

I am not running a linear. I am running QRP 5 watts. Relay K1 is not required for barefoot operation:

" … this relay does not control any of the internal functions of the transceiver…" ( a direct quote from page 2-3 of the Corsair II manual )

So I start investigating, and find that it is easy to silence K1 for barefoot operation.

All one has to do is disable the circuit that activates the coil of relay K1.

From the 80978 Control board schematic ( page 3-32 of the CII manual ) it is obvious that transistor Q10 switches the K1 coil to ground to energize the relay.

Easiest way to disable this function is to short the base to emitter junction of Q10. Now Q10 will never be activated. And the drive circuitry into Q10 will never be able to tell the difference; and will not be compromised.

Q10 is located on the corner of the circuit board about a half-inch inch from K1.

I used a miniature alligator clip, and clipped it across the base-emitter leads of Q10.

Reverse modification is a obviously a simple matter.

Now my Corsair II works like a dream. Velvet smooth QSK and PTT, nice and quiet like the Scout.

I never did like noisy relays …


Or, simply lift one end of Q10's base resistor and never worry about shorting a current source to ground.

-Paul, W9AC

Easier yet. Cram a piece of cardboard between the relay's contacts. It works and is easily reversable.


February 27, 2008

Improvising on the mod on tentecwiki I pulled up one end of the 22k resistor in the base circuit of Q10 on the control board and was rewarded with silent QSK. I've never used a linear amp, so I don't need that relay clacking at the end of each character. I've ordered an auto antenna tuner for the Corsair. Once that arrives, I can really get busy!

Jim Stoneback

Good Idea Jim,
When I had my Corsair II I also used a AL-80 Linear for SSB only so I needed the relay but didn't like hearing it when barefoot. Here's what I did. I use an Astron PS so never used the power on switch on the CII. I disconnected the wires to the power switch and connected to the end of the resistor so when I needed the linear I simply pulled the power switch to on which turned on the relay and the switch was still labeled correctly. Need more power pull the power switch!

73 Jim K4CGY

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