-=> On 08-18-97  12:05, Jeff Edmonson said to Ivy Iverson, <=-
-=> About transformer,..." <=-
-=> I've moved this over here, out of the SALE echo ;-)
-=> -=> On 08-16-97  16:40, Jeff Edmonson said to Ivy Iverson, <=-
-=> About transformer,..." <=-
 
 > Hi, Jeff;
 
 >  z> JE> Looking for a 7.5v @ 12Amp transformer.
 >  z> JE> Anyone?
 >  z>That's an oddball.  What's it for?
 >  JE> Filaments for a Eitle McCullogh 450TL (Eimac).
 >  JE> The BC-610 used to use a singe 250TH in the final, modulated by a 
air
 >  JE> of  100TH's.
 
 II> AH YES!  I remember the BC-610!  Worked on them in the
 II> Army!  Wish I had one, but in the interest of avoiding moderator
 II> action, I say no more.
 
 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.
 
AH!  A medium-power AM loudenboomer!  :->
 
 JE> Thought about using the 450TL's, but with a pair of 'em, it's
 JE> somewhere in the  area of 7.5v @ 25Amps, just to light up the
 JE> filaments! 
 JE> Instead, I belive a more wise choice would be to use 4 811's in
 JE> push-pull  parallel.
 
Ok, remembering that 250 watts of carrier needs 125 watts of audio for
100% modulation if you are plate modulating... a good deal less if you
are using grid modulation.  (I have forgotten how much a 450TL can put
out - seems to me it's around 200-250 watts).
 
Personally, I would use a scope connected for a trapaziod pattern as a
modulation indicator on any such rig.  (RF output to the vertical plates
and AF input to the horizonal plates).  As long as you bring it to a
point without getting a flat line on peaks you are 100% modulated.
Check the handbook, (at least the older ones), for details.
 
 JE> I have some other ideas for how a properly modulated AM rig should
 JE> work, and  definatly ways of increasing the fidelity!
 
Speech processing would be a good thing to have, at least a compression
amplifier, with about a 2.5-3 KHz lowpass filter on the output.  Beyond
that, a good-quality AF amplifier should be all you need.
 
 JE> Soon, I'll have a text file from John/WA5BXO on how to feed class B
 JE> modulators. Talked to him briefly last night on the telephone, and he
 JE> told me some of it - GREAT technical data, there!
 
Assuming you aren't severaly limited by finances, I would suggest
transformer coupling for the modulator input and output.  Are you
planning to use solid-state or hollow-state for the audio up to the
modulator?
 
Please keep me informed on how it's going.
 
Catch you later... Good luck!
   Ivy
 
 
 
... Keep the shack warm: Run radios with tubes!
 
     
 
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