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Title: Johnson 500 VFO question Post by: N2IDU on August 19, 2011, 02:58:55 PM I can hear the vfo running weakly on my receiver which is an HRO 50T. This is very vexing. My yacht boy 400 picks up the vfo running as well when placed within 3 feet or so of the 500. I have tried adjusting the keyer pot R109 which has no effect in reducing this malady. I thought this topic was covered in a prior post but I couldn't locate it.
Thanks, Peter N2IDU Old Shincracker, Vt. Title: Re: Johnson 500 VFO question Post by: w4bfs on August 19, 2011, 03:57:59 PM I've gotten a 500 rf deck and am gathering up parts for hb hv/mod deck ....took a fast look at the schemat .... first step is try a new 12au7 keyer ... if that doesnt help then going to have to determine why the 6au6 vfo is not getting cut off ... I have seen leaky bypasses in Rangers/V2 cause a similar problem
Title: Re: Johnson 500 VFO question Post by: WQ9E on August 19, 2011, 08:42:40 PM Peter,
As suggested try a replacement keyer tube. Is the Viking 500 working properly otherwise? Have the bias filter caps been replaced? Leaky/lost capacitance bias caps will create a number of problems including keyer problems. Also, measure the voltages on the keyer tube and this should lead you to the trouble. Title: Re: Johnson 500 VFO question Post by: W1ATR on August 20, 2011, 09:06:55 AM That might have been my post your looking for. Had the same prob a couple years ago and I kind of found it on accident. Mine made receiving impossible as it would throw my 390a a nice 50+ signal. Here's what I did.
Pull the RF deck out of the cab and flip it over. Right near the fan is r168. Its a 4" long wire wound with three taps used to set bias voltages for different modes ("tune", cw/am, and ssb). The tune tap sets the bias for the clamp tube, (I think) and it was loose enough to lose contact. Snugged it up, and the problem went away. My 500 is a daily driver on 10m and the problem hasn't returned since. 73 J Title: Re: Johnson 500 VFO question Post by: WD8KDG on August 20, 2011, 11:07:53 AM Peter,
Is this something new, was the 500 operating correctly in the past? When I brought my Junkston 500 home some hammy hambones had made some mods to the keying circuit. Those mods and others were removed before the TX was powered up. Craig, Title: Re: Johnson 500 VFO question Post by: N2IDU on August 20, 2011, 03:49:39 PM Ok, It now works perfectly thanks to the suggestion of replacing the keyer tube 12au7. I did pull this tube and test it in my Hickock and found nothing wrong with it. Replacing the same with a nos 12au7 cured the problem instantly. Thanks for all the help. This is a great forum. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Peter N2IDU Old Shincracker, Vt. |