[Heath] DX-60A Grid Tune Issue

[Robert Wood]

Thank you Ken, 

Actually the maximum drive level for 40 through 10 meters is less than .5mA
(1/2 mA), not 5mA.  

Hopefully I will get some time this afternoon to adjust L-1 per your
recommendation and let everyone know.  I agree with you there is no
information in the manual regarding L-1 adjustment.  The manual only says
"The plate circuit of V1 is untuned for 80 meter operation, and is slug
tuned by coil L1 for operation on 40 through 10 meters".   

I will also try bypassing the low-pass filter then tune up to see what
affect this has.

Thank you,

Bob K5MBA



-----Original Message-----
From: Kenneth G. Gordon [mailto:kgordon2006 at frontier.com] 
Sent: Friday, April 07, 2017 5:09 PM
To: Robert Wood
Cc: Heath at puck.nether.net
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.

Ken W7EKB

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