[Heath] DX-60A Grid Tune Issue

[Glen Zook]

You need to read his original message again!  He said 0.5 mA, not 5 mA.  I have found that most of the 6146 family of tubes will put out full power at around 1.75 mA but not below.  Between 2 mA and 2.5 mA grid current per tube is a good target.  Anything above 3 mA will definitely shorten the life of the tube.


The "." before the 5 is very easy to miss!

 Glen, K9STH 
Website: http://k9sth.net

      From: Kenneth G. Gordon <kgordon2006 at frontier.com>
 To: Robert Wood <radiorob at swbell.net> 
Cc: Heath at puck.nether.net
 Sent: Friday, April 7, 2017 8:22 PM
 Subject: Re: [Heath] DX-60A Grid Tune Issue
   
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.

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.


   
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