Topband: 160-Meter Key Klix
gswynar at durham.net
Wed Dec 28 15:03:23 EST 2005
Good Afternoon All,
Ah, the price of success...!
Now that I've got a better transmitting antenna here for Topband, my extra signal strength around the continent has raised comments that my Icom 751A is a tad "...key clicky"...Murphy is alive & well, & making 160-meters his home.
But thanks to encouraging & constructive comments from Tom (W8JI), I took a good look at the rig, service manual in hand. I played some with the potentiometer that controls the "...transmitting initiation timing" (for want of a better description!), & have it set to what looked best on my SB-610 scope, i.e. fully clockwise...but! As many of you know only too well, a visual view alone is NOT necessarily the best way to adjust for diminished clicks --- it's as much a QUALITATIVE thing/measurement, as it is a QUANTITATIVE one...
Anyway, I went on & checked the bias on both the driver transistor(s) stage, & the final RF amplifier stage --- to my surprise, the bias setting on the driver(s) indicated 150 ma. ...it SHOULD have read 100 ma.! Significant, or not, I re-set the pot controlling this back to "factory specs", and buttoned-up the final stage...
I would be VERY appreciative, gentlemen, if you might take a moment of your time to listen for me on the band to-night, with a critical --- but not TOO critical! --- ear cocked for Key Klix emanating from the rig, as it is configured now. Let me know by direct e-mail of your verdict, at your convenience, with my thanks in advance...it'd be especially noteworthy to see how mine might compare to other stations of similar signal strength. I'm STILL convinced that all CW signals are accompanied by key clicks to a greater, or lesser, degree, dependent upon received signal strength.
What I may try next is to reduce the input power to my linear amplifier --- presently, the homebrewed ol' pair of 813's in it are pretty much max'ed out, running the limit at some 2500 VDC / 400 ma on the plates, with just under 100 ma. of grid current...dependent upon feedback from to-night's mods, I may well try reducing input to 750 watts, i,e, 300 ma. plate current. The difference to G3FPQ's ears at a 25% reduction like this will be negligable(sp?), I'm sure...!
Stay tuned --- whatever I might learn from all this, I'll gladly share with the group here...
~73~ Eddy VE3CUI - VE3XZ
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