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-=> On 08-20-97  13:11, Jeff Edmonson said to Ivy Iverson, <=-
-=> About transformer,..." <=-
 
Hi, Jeff;
 
 II> AH YES!  I remember the BC-610!  Worked on them in the
 II> Army!  Wish I had one...
 
 JE> Got a pair of 250TH's here, in a homebrewed AM rig, that I'm currently
 JE> in the  process of building a modulator for.
 
 JE> I wouldn't call 2500v @ 350mA quite MEDIUM power, in respect to Ham
 JE> power  limits ;-)
 
Ok, 875 watts in... VERY respectable!  Should be good for around 650 W
out.
 
 JE> But, I won't be using that much - more like 2kV @ 200mA, for 400w
 JE> input to the  final.
 
400 W in... less than an S-unit difference.   :-}
 
 II> Ok, remembering that 250 watts of carrier needs 125 watts of audio
 II> for 100% modulation if you are plate modulating...
 
 JE> I've grown up around BC-610's, ART-13's, DX-100s, Viking Rangers
 JE> Viking 1's and II's and other various AM tranmitters.  It all depends
 JE> on how much clarity and  quality you're looking for, out of an AM
 JE> signal. 
 
True, however no matter how Hi-Fi you get it and no matter how perfectly
you reproduce your voice, there is only so much that you can do and
still stay within the 3 KHz (+ or -) audio bandwidth which is required
for intelligable speech.  If you were setting up a commercial AM BC
station I can see going to enormous lengths to get perfect response,
but for Ham use, IMHO, it isn't really necessary to try to be the best
sounding station on the bands.  Just a bit of QRM or QRN and it's
nullified!  (Sorry, I'm not trying to shoot you down, here, just stating
my personal opinion.  Your milage may vary).  ;->
 
 JE> Since the absolute most power that can be run, on ANY mode is 1500w
 JE> PEP OUTPUT  (something I -never- agreed with.  How can it be properly
 JE> measured?) in AM  terms, that comes down to around 500w DC input to the
 JE> final, or around 375w  carrier output.
 
GAKKK!  I agree that when they changed the limit from 1KW input to 1500W
PEP, it was NOT a good thing!  It's plenty easy to multiply E X I and
say, "OK, 980 watts, I'm legal," but measuring actual PEP isn't the
easiest thing in the world without expen$ive equipment!  (Ok, a
calibrated O-scope will work on HF, but when you get over 50 MHz, even
those get expen$ive!)  Then you have to do the math.
 
I suppose, though, since the RMS output of SSB it is difficult to
measure the max instantanious power, (Ip or Ic), but is it any easier
to measure the RMS of the carrier?  I think not.   
 
 JE> Remember, that PEP out, at 100% moudlation, is 4 times the carrier. 
 JE> 1500w PEP  out is 375 x 4.
 
UG!  I have no plans of going high power, but I STILL want the 1KW limit
back, for safety if nothing else.  Maybe they just figured that there are
so many of us Hams now that they needed to cut us back a bit.  :-<
 
 JE> The nice thing about Eimacs tube designators, is you could immediatly
 JE> tell what the plate dissapation was, byt the number of the tube.
 
I was unaware of this... or had forgotten it in the last 30 years or so.
 
One disadvantage of that system is that that's the ONLY thing it tells
you about the tube.  The "conventional" numbering system describes the
tube nicely.  For instance, 6L6 (and it's variations): 6.3 V heater,
beam power pentode: 6 elements, (Heater, Cathode, G1, G2, G3/beam-forming
plates, plate).  12AT7/12AU7/12AX7 family: Twin triodes with 12 V
heaters, (which can be paralleled for 6V), and in SOME applications
are directly interchangable.  Tube IDs like 250TH only tell one thing
about the tube, so you have to grab the manual if you want to
know more.   :-}
 
 JE> A pair of 450TL's, according the 1957 ARRL Handbook ... will run
 JE> every bit of 1kW output.  Naturally, this much isn't needed, but
 JE> does provide  the necessary overhead, to increase (dramatically!)
 JE> the QUALITY of audio  comming from the speech-amp.
 
True, you don't want to run tubes - or anything else for that matter -
at 100% ratings, for component life if nothing else.  And having a
cushion gives you a little breathing room. (Better linearity)
 
 II> Personally, I would use a scope connected for a trapaziod
 II> pattern as a modulation indicator on any such rig.
 
 JE> Sampling RF, wiht a 'loop' type of antenna, or possibly a coil, to
 JE> view the  carrier, and then the audio imposed on it is better, because
 JE> you can instantly  see when/if the amount of audio ever reaches/exceeds
 JE> 100%.  Looking close  enough to the audio on the 'scope, will also show
 JE> how 'smooth' it is, instead  of 'peaked', depending on what mic you're
 JE> using.
 
You can get the same information from a trap pattern... when it hits a
perfect triangle you are at 100%.  If you get a line off the point of
the triangle you are overmodulated.  If the sides are perfectly
straight you are linear, if they are curved you aren't.  Personally I
find it easier to interpret at a glance than watching the envelope.
 
 JE> Don't agree that processing is necesarily good - nor compression. 
 JE> Perhaps a  little compression, but only if you have a room full of
 JE> hams, who you'd like to modulate the rig, who are a distance from the
 JE> microphonium.
 
I do not consider it wise to work a mic from more than a foot away
for the reasons you mentioned.  Ever watch an announcer on radio/TV?
With few exceptions, they are NEVER more than a foot or so from the mic,
(usually about 4-6 inches), and they are in a soundproof studio, not the
average Ham's shack in the basement, living room, or den.  More than a
foot away and you will get a lot of room noise, and that certainly won't
improve your intelligability at the other end!
 
 
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