[AMRadio] The Viking II is FINALLY starting to work


Ellen Rugowski ellenjoanne2003 at sbcglobal.net
Sun Feb 3 09:01:22 EST 2008


Hi Everybody,

As you may recall, I mentioned some time ago, that the plate current on the finals of the Viking II I got dirt cheap,  was well over 350 mA even without keying it down in CW, when the high voltage was turned on.  A lack of time and some false leads kept me from finding the cause until late last night, when spending several hours trouble shooting the Viking  II (two of them on the phone with Rodger, WQ9E, giving additional suggestions for things to check), determined the problem.   Biasing to the finals turned out to be OK.  BUT, the clamper wasn't doing a thing to clamp the current to the finals. It turned out that whoever owned my Viking II sometime in the past, replaced the clamper pot, with a multiturn, audio-style pot.  Not only that, they had it's function reversed. As a result, the clamper circuit was almost completely unclamped!  I was able to reset the clamper pot for 10 mA of plate idle current with the high voltage turned on.  

The Viker loaded up, and finally produced power (about 125W on CW, key down). Plate current is not maxed, but still may be a little high (about 220 mA), on key down.  Also. a couple of times when I keyed down, I saw some smoke curling up out of either the area of the finals, or the loading capacitor.  I'm not sure which is the culprit.  I will admit, that the rig was very dirty/dusty, when I first opened it up (I spent a fair amount of time vacuuming in it).  So, I'm not sure if it's dust cooking, or if a component is giving problems.  Per Rodger's suggestions, I'll check things out some more today, now that I'm not so tired (I didn't finish working on it until almost 11:30 PM).  It may also be possible that the parasitic suppressors on the finals are going bad (their wiring looks a little ratty), and as a result the resisitors inside of them are carrying all of the load, and as a result, are starting to smoke.  

73,
Ellen - AF9J


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