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Author Topic: Viking ll CDC no grid drive on AM  (Read 4694 times)
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WB4AQL
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« 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
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KA3ZLR
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« Reply #1 on: August 14, 2011, 11:51:42 AM »
Hi,

Dirty Switch...? Roll Eyes


73
Jack
KA3ZLR
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WB4AQL
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« Reply #2 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.
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WB4AQL
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« Reply #3 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.
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WB4AQL
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« Reply #4 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
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WD8BIL
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« Reply #5 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.
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WB4AQL
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« Reply #6 on: August 21, 2011, 04:40:13 PM »
Yep. It was just mode switch contacts that needed cleaning. Thanks to all!

Michael  WB4AQL
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KA3ZLR
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« Reply #7 on: August 21, 2011, 05:20:12 PM »
Quote from: KA3ZLR on August 14, 2011, 11:51:42 AM
Hi,

Dirty Switch...? Roll Eyes


73
Jack
KA3ZLR

Hi,

 I'm glad that's all it waz... Smiley

73
Jack
KA3ZLR
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WA2ROC
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« Reply #8 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.
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Dick Pettit WA2ROC 
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WB4AQL
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« Reply #9 on: August 22, 2011, 01:33:06 PM »
Hi! Hi! We'll see how she do!

73, Michael
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