[AMRadio] Re: Modulation transformer ID and repair

[Brett Gazdzinski]

Don,
I don't get into the negative cycle loading much, its
more of a protection device, to prevent splatter and so on.
I think anything that changes the input waveform is distortion.
I do run some compression, to compensate for moving around while
talking.

The mike preamp does limit the peaks (one of those berringer things),
but not much.
 
Brett
N2DTS
 
> 
> >I limit my quick peaks in the mike preamp, and include negative
> >cycle loading in all RF decks, but don't push things much.
> 
> I don't use negative cycle loading or ultramodulation, but I do take 
> advantage of the natural asymmetry of the human voice.  Mine 
> tends to run 
> about 135% positive when I limit the negative to 100%.  The 
> ratio would be 
> more like 2:1 if I clipped off a few excessive negative 
> peaks. I usually run 
> about 640 watts DC input to the final.  Considering the 
> losses in the PA 
> tank circuit, the matching network at the transmitter output, 
> the feedline 
> between the shack and the tower site, and the remote antenna 
> tuner at the 
> base of the tower,  I'd be surprised if I'm getting as much 
> as 400 watts 
> carrier output to the antenna.  When I talk, the modulatior 
> plate meters 
> just barely wiggle beyond static plate current, unless I 
> whistle or make a 
> sustained tone.  With a sinewave signal from a generator I 
> can make each 
> modulator tube draw up to 400 ma!  The only "processing" I use is the 
> Universal Audio/Urei Model BL-40 Modulimiter (the only 
> solid-state device in 
> the station except for the homebrew cw keyer).
> 
> 
> >There are people on the band who run/can run excessive positive
> >modulation, but you need a special detector I guess, because 
> they sound
> >bad in my shack when they do.
> 
> I just make sure there is no flat-topping on positive peaks 
> or bright spots 
> on the baseline in the negative direction.  I once tried 
> ultramodulation, 
> but I think I gained much more distortion than talk power.  
> Most reports 
> indicated the audio was no louder, but had a scratchy sound.  
> The most 
> effective thing I ever tried for "talk power" was high level 
> symmetrical 
> speech clipping back in the 60's, but it added audible 
> distortion, and I 
> went through about half a dozen modulation transformers in 
> about as many 
> months, ranging in ratings from 500 to 2000  watts.  After I 
> abandoned the 
> high level clipping, I havn't lost a single modulation 
> transformer since.
> 
> Don K4KYV
>