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Title: Johnson 500 problem Post by: Steve W8TOW on July 25, 2006, 09:53:18 AM Hey Gang, got one for ya to think about....
My Johnson 500 just developed a problem. On CW, the keyer pot has no effect, but does have the OSC cuttoff, keying is fine, all bands NO CHIRP. On AM, the OSC no longer cutsoff (thus runs when UNKEYED now) The keyer pot has no effect either AM/CW.... AM/CW BIAS is -50 VDC as spec... The Keyer tube (12AU7) was found to have a open filment, but still after replacing it with a new 12AU7, the keyer circuit can not be adj.... SO....just a run down, NO KEYER POT ADJ AM/CW (POT & TUBE IS GOOD) CW GOOD WAVE FORM AM OSC REMAINS ON IN STANDBY.... BIAS GOOD any ideas??? 73 steve 8tow Title: Re: Johnson 500 problem Post by: Steve W8TOW on July 28, 2006, 12:11:30 PM :) :) :) :) :) :) :) :) :)
Well, If you look long enough, ya can find anything! Once I got the keyer working properly, I evaluated the interconnecting cable between the PS & RF deck. This cable carries AF from the driver, & the "hot" side of the CW key input, down to a relay....In standby, the relay is open, and B+, AF, and the key line is open. So.... the keyer circuit was sick the cable was bad AND one of the 4 contacts of the relay was touching all the time...it just happened to be the key line contacts! WOW, lot o work for just a small problem... 73 steve 8tow Title: Re: Johnson 500 problem Post by: The Slab Bacon on July 28, 2006, 12:58:26 PM Steve, AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Be glad that you didnt have to go the trials and tribulations that I went through with the 500's cousin, the Invader 2000. I was one cigarette away from the BFH and a gallon of gasoline!! Sometimes these things will totally test your patience and perseverance! However the end result is uaually the effort. It is now one of my favorite transmitters!! The Slab Bacon |