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Title: Viking ll CDC no grid drive on AM Post by: WB4AQL on August 14, 2011, 11:50:01 AM Yet another grid drive query? Oscillator and buffer tune properly in CW mode. Switch to AM, key the tx, no grid drive. Did a quick swap of the 6AU6 oscillator and 6AQ5, to no avail. Had it on the air last night, switched on this morning, nada.
I`m thinking maybe a resistor has opened up, but before I start looking, just wanted to throw this out for comment. Got to be somewhere between the oscillator and the PA. Thanks, Mike WB4AQL Title: Re: Viking ll CDC no grid drive on AM Post by: KA3ZLR on August 14, 2011, 11:51:42 AM Hi,
Dirty Switch...? ::) 73 Jack KA3ZLR Title: Re: Viking ll CDC no grid drive on AM Post by: WB4AQL on August 14, 2011, 11:54:54 AM Maybe. I cleaned`em recently, but will have a look. I did run the switches back and forth today. By the way I`m running xtal control with this rig.
Title: Re: Viking ll CDC no grid drive on AM Post by: WB4AQL on August 14, 2011, 02:29:10 PM I guess I should rephrase this problem to say it seems that the oscillator is producing ample grid current, but the PA 6146s are not drawing grid current. Does that make more sense? Do the 6146 grids open up when they fail?
I`ve had grid current go away due to a bad drive pot on other transmitters, but this seems to be different. HV is OK as far as I can tell. Title: Re: Viking ll CDC no grid drive on AM Post by: WB4AQL on August 14, 2011, 03:52:40 PM Well. I pulled it off the bench and checked values. All seemed well. Ran the switches back and forth. Everything OK now. Had to have been a switch contact somewhere.
I promise I don`t make this stuff up... Thanks to all. Mike WB4AQL Title: Re: Viking ll CDC no grid drive on AM Post by: WD8BIL on August 15, 2011, 01:16:28 PM In the phone position put a key in the cw key jack and close the shorting bar. Ifn u get grid drive the wiring, or contacts, on the mode switch are the culprit.
Title: Re: Viking ll CDC no grid drive on AM Post by: WB4AQL on August 21, 2011, 04:40:13 PM Yep. It was just mode switch contacts that needed cleaning. Thanks to all!
Michael WB4AQL Title: Re: Viking ll CDC no grid drive on AM Post by: KA3ZLR on August 21, 2011, 05:20:12 PM Hi, Dirty Switch...? ::) 73 Jack KA3ZLR Hi, I'm glad that's all it waz... :) 73 Jack KA3ZLR Title: Re: Viking ll CDC no grid drive on AM Post by: WA2ROC on August 22, 2011, 10:05:44 AM That sounds like a really big problem. Maybe you need to sell the VII to me at Shelby in 2 weeks.
Title: Re: Viking ll CDC no grid drive on AM Post by: WB4AQL on August 22, 2011, 01:33:06 PM Hi! Hi! We'll see how she do! AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
73, Michael |