[AMRadio] Ranger driving SB220


Jim Wilhite w5jo at brightok.net
Tue Feb 12 12:12:11 EST 2008


 >It is also easy for the modulator
> to over modulate because it doesn't need to deliver as much current.
>
> John, WA5BXO


This is probably the main cause of trouble using an amp with a driver as 
described.  I constantly hear crappy audio on the bands with the 
configuration.  Many do not understand meter readings of Class A, AB and 
B amps anyway so they tend to overdrive them with audio.

Not only that they do not monitor the output waveform.  Additionally 
many do not know how to interpert what they see.  So all in all, I 
believe, the best way to avoid hidden troubles is to operate an exciter 
or transmitter is near its design parameters and reduce power with the 
attenuator.

Last night was a perfect example.  One station who was using a solid 
state exciter to drive a tube amp was splattering all over the place and 
the person (s) he was in contact with could not hear the problems.  If 
they did, they either wouldn't tell him or did not know what was 
happening.  I was about 5 kc below and when I heard the buckshot tuned 
up to see who it was.  They were all telling him that he sounded fine 
and what the meters should read.  Wrong of course.

All this assumes the exciter is operating properly.  That can be a crap 
shoot with a lot of this old gear.  Especially a transmitter pulled from 
a barn and put on the air with mimimual rework.

Jim/W5JO



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