[Heath] DX-60A Grid Tune Issue

[larrysheldon at cox.net]

---- "Kenneth G. Gordon" <kgordon2006 at frontier.com> wrote: 
> On 7 Apr 2017 at 14:44, Robert Wood wrote:
> 
> > I have a DX-60A that has more than enough drive on 80M and tunes up great - about 75 watts 
> > out.
> >  
> > Unfortunately 40M thru 10M is QRP.  The maximum drive level for 40M is about 2ma, and 20M 
> > through 10M less than 5ma.


I have no current information---many years since the last time I touched a knob.

BUT.... this would make more sense to me if that said "... through 10M less than 0.5ma."


> 
> Hmmmm....6146 requires no more than 2.5 mA grid drive. It sounds to me as though your 
> driver is providing enough drive. 5mA is WAY too much grid-current for a 6146. If that level of 
> drive current is held too long, the tube will go "flat".
> 
> >  The Final Tune and Final Load controls have little affect on the 
> > meter in plate position.
> 
> THAT is where the problem lies: in the transmitter output circuitry....at least IMHO. I think you 
> should be looking carefully at the PA plate circuit, not the driver. Perhaps the low-pass filter is 
> defective. Try bypassing the low-pass filter then try tuning up. See if that makes any 
> difference. There should be a sharp plate current dip at resonance. If you don't get one, then 
> something is not right in the output circuitry.
> 
> > Does anyone know how to adjust L1?  I cannot find any information in the manual other than it 
> > says it is for 40 through 10.  I tried adjusting it up and down a little with no change.
> 
> That is meant to be broadly resonant in the center of the 40 meter band. Connect an 
> oscilloscope probe to pins 2 and/or 9 of V-2, the driver, key the transnitter in CW and while 
> holding the key down, adjust L-1 for maximum on the scope. I doubt if you will see much 
> effect, though. The peak should be very broad.
> 
> Ken W7EKB
> 
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