[Heathkit] DX-100B - spurs everywhere.

[Glen Zook]

You are getting way too much power output!  I know that Heath spec'd the transmitter at 180 watts input on CW and 160 watts input on AM phone.  However, the 160 watts input on AM phone is considerably in excess of the maximum power input specified by RCA for AM operation.  RCA specifications say a maximum of 67.5 watts input per 6146 or 6146A/8298 and that means 135 watts maximum input on AM.  Running the tubes at like 120 watts input for the pair will definitely result in considerably longer tube life.  Running them at 160 watts input reduces the life by at least 75% and often more.

Running 90 watts output, like you mentioned in your first message, is more like it and reducing that to like 75 watts on 75 meters will make the final amplifier tubes a lot more happy and they will last considerably longer.  Frankly, the operator at the other end is not going to notice the difference between 75 watts and even 125 watts.  But, the final amplifier tubes will definitely notice it!

On CW, since the accepted power factor is 40% of the peak power (this is because of the duty cycle of CW versus AM which is 100%) you can get away with running more power although running CW at slightly reduced power will make the final tubes a lot happier.
 
Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: Rick Poole <wa1rkt at arrl.net>
To: heathkit at mailman.qth.net 
Sent: Thursday, December 1, 2011 8:22 PM
Subject: Re: [Heathkit] DX-100B - spurs everywhere.
 

A couple of people told me that the oscillations I was seeing on 
phone were likely neutralization, and one person told me that 
"Neutralization can be done in several well-documented ways".

So, I went searching and found a few...

http://home.roadrunner.com/~boatanchors1/dx-100%20neut.html
http://home.roadrunner.com/~boatanchors1/posting.html
http://groups.yahoo.com/group/heathkit/message/19871

... not much of anything else.

So, I tried adjusting the little wire that pokes into the PA 
compartment and managed some pretty dramatic results... now I get 
spurs on both AM and CW and they are quite readily generated.

Put the neutralization wire back where it was, no real 
improvement.  There is no position of the neutralization wire that 
shows any significant difference in behavior.

I think it always did this on CW, I just had to get the plate farther 
out of resonance on the high side before it would do it.  I can still 
tune the rig on CW and it will be stable, but I have to be careful 
not to get out of resonance on the high side (AMPLIFIER pointer 
points to higher numbers; plate tuning cap is more meshed).

One thing I noticed... one of the articles on neutralization 
emphasized keeping the grid current around 4 ma, and the DX-100 
manual cautions against running the grid current above 6 ma and 
recommends keeping it at around 5 ma.  My grid current will not go 
above about 2.5 ma no matter what, at least not on 80 meters (haven't 
tried any other bands yet).  And yet, when it is stable and putting 
out the correct frequency, I can easily get between 100 and 125 watts 
out at a plate current of 200-250 ma, just like the book says.  So I 
can't figure out why the grid current is so low.

Next step is to check all the tubes in the tube tester, and then 
wrestle the thing over to the workbench and start loosening and 
retightening hardware and checking resistor values (don't have a way 
of checking capacitor values yet).

Anybody have an idea off the top of their heads why the grid current is so low?

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