[AMRadio] Ranger Modulation


Gary Schafer garyschafer at comcast.net
Thu Nov 16 12:01:18 EST 2006


You can't reverse the plate leads on the modulator tubes because it uses
negative feedback from a winding on the transformer. Reversing the plate
leads puts the feed back in phase rather than out of phase. It will
oscillate!

First check to see that you have proper grid current on the 6146. Low grid
current will not allow full positive peak modulation because the tube runs
out of steam with low drive. It is much more important to have proper grid
current with AM than it is with cw. The tube has to have enough emission to
handle the peak power 4x the carrier.

Be sure the screen voltage is high enough on the 6146.

Be sure that you are not overloaded - more power than the transmitter is
rated for. If you have it loaded too heavy again the tube runs out of
emission and will not allow the modulation peaks to go high enough.

Try another 6146. 

73
Gary  K4FMX

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of Jack Schmidling
> Sent: Thursday, November 16, 2006 10:28 AM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] Ranger Modulation
> 
> Larry Taft wrote:
> > Try reversing the phase of the audio by swapping the output leads of the
> > modulation xfmr.
> 
> First I swapped the tubes to no avail.  I then swapped the wires and now
> have a strange buzzing that I can not locate but it shows up on the
> audio with the gain at zero.  Don't know if I barfed something up or not
> but I vaguely remember reading somewhere that this an an indication to
> reverse the leads.
> 
> 
> > Weak tube in the audio chain causing lack of gain needed for the
> > positive peak.
> 
> Just ordered new audio tubes.
> 
> Now I notice another discrepancy..... the manual that came with it says
> to adjust the mod current to 75-90 ma.  The manual that Rick sent me for
> the new version which I seem to have says 55-70 and no clue why the
> difference.
> 
> Which is correct and should I make an allowance for using 6L6's instead
> of 1614's?
> 
> js
> 
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