[AMRadio] VFO vs XTAL


Jim Wilhite w5jo at brightok.net
Wed Oct 17 21:23:42 EDT 2007


The old way to know how much grid drive is needed is to monitor the 
transmitter power output and crank up the knob until there is not more 
output with increasing gird drive, then back off to max power.  The 6146 
family of tubes are spec in CCS, @ 2.8 ma @ 475 volts.  In ICAS they 3.4 
ma @ 600 volts which is what the Viking/Valiant has on the plates.  This 
is all with 250 volts on the screen.

I, too, would like to know what rig you are using Rick,  The 122 VFO 
probably has about 60 V peak output or near 100  P to P.  More than 
enough to drive a crystal stage, unless one wired different.  Check the 
Crystal/VFO switch in WRL GK 500 to see the difference.

Jim/W5JO



> Rick Brashear wrote:
>> It doesn't matter as far as the operation is concerned IF there is 
>> enough
>> drive.  I'm not getting sufficient drive from either.  However, I am 
>> getting
>> much more drive from the internal crystal oscillator than from the 
>> Viking
>> VFO and I found that strange.  I would have thought the VFO would put 
>> out
>> more RF than the xtal oscillator.
>>
>
> What rig is this in, Rick?  MAn, the Viking 122 VFO, at least on the 
> Viking II, has -plenty- of drive!
> I keep my grid drive control down, on 80m, around 2.5 or 3 on the 
> knob.  That gives me around 7.5mA of grid drive for the pair of 6146's 
> (yeah, Ellen - I've been meaning to send you that correction - Johnson 
> says a single 6146 needs no more than 2.5mA of grid drive, the pair in 
> the Viking II needs 7.5mA of grid drive, and I'm guessing (someone 
> tell me for sure) that the Valiant, with it's (3) 6146's needs around 
> 10mA of grid drive?) and if I crank the knob up to around 5 or 6, then 
> I've in excess of 10mA of grid drive on the pair of 6146's.
>
> -- 
> Driving your AM Rig without a scope, is like driving your car at 
> night, without headlights. (K4KYV)
>
> --
> 73 = Best Regards,
> -Geoff/W5OMR



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