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Title: Need help with a Johnson Valient vfo problem Post by: Knightt150 on April 11, 2011, 05:29:57 PM I have a friend who has a nice valient it worked great for some time, but all of a sudden he had no grid drive. We put crystals in and selected one and we had great grid drive and power out. We switched to the VFO and had output on 40m only, all tubes and circuits were checked and the BAND SWITCH was thoroughly cleaned. Has anyone got any ideas what to check next.
John W9BFO Title: Re: Need help with a Johnson Valient vfo problem Post by: WA1GFZ on April 11, 2011, 08:37:33 PM check the cam switch maybe it slipped
Title: Re: Need help with a Johnson Valient vfo problem Post by: Knightt150 on April 14, 2011, 08:58:33 PM The cam switch was checked and was found tight. New crystals were installed on 75 today and worked great. Still looking I guess unless someone points the way.
John W9BFO Title: Re: Need help with a Johnson Valient vfo problem Post by: WA1GFZ on April 15, 2011, 01:04:43 PM check the coupling cap at the VFO output. maybe parallel it with another of the same value. It is a low value so it doesn't load the oscillator. Look at the output with a scope. and see if it is working. Check the VFO screen dropping resistor.
Title: Re: Need help with a Johnson Valient vfo problem Post by: kg8lb on April 20, 2011, 11:20:31 AM Make sure there is B+ 0n the plate of the oscillator tube. The series dropping resistor, ahead of the regulator tube is notorious for opening up or worse ! (18K if I recall correctly) . Many folks move the resistor outside and replace it with a 5 or 10W resistor. I use a 5W but leave it inside the VFO housing in the original location.
Been a while since we chatted on 40M , John. Hope you got that T150 sorted out. Gary Title: Re: Need help with a Johnson Valient vfo problem Post by: KB2WIG on April 20, 2011, 10:32:28 PM Google "chernobyl resistor" AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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