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[AMPS] info on power supplies

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Subject: [AMPS] info on power supplies
From: (2)
Date: Thu, 12 Jul 2001 10:31:06 -0700
>I'm building a 'retro' transmitter for high quality amplitude 

/\  John - I have done AM with plate-modulation and with low level 
modulation using an AN-612  modulator IC - followed by a >1499w-PEP 
linear amplifier.   With traditional plate/anode modulation, some IM 
distortion could be heard.  With the AN-612 modulator/linear set up, no 
distortion could be heard.  /  note:  the Trio-Kenwood TS-440, 930, 940, 
et cet. - as well as some other mfg's transceivers use the AN-612 for 
generating AM and SSB.  Motorola makes a similar modulator-IC.  

>The RF part is to be a Johnson 500 (single 4-400A), and 
>the power supplies,  modulator and control relays are homebrew. To 
>pay homage to tradition and have the bouncing violet glow when I say 
>1-2-3, I started with 866A mercury vapor rectifiers. But due to space 
>limitations on the big chassis and the size of the ancient iron I 
>have acquired, now I am using silicon diodes. What was interesting in 
>all this is that after reading old handbooks (both ARRL and Editors 
>and Engineers - pre Bill Orr and after) you can observe the trend 
>away from L input filters and center tapped secondaries with 2 
>rectifiers >>>> to Cap. input, 4 diode full wave brides, or doublers 
>for SSB amps. With the change to silicon came higher peak current 
>ability (than tube rectifiers) and the change in filter 
>configurations. I hear some of the folks here using as much as 100 uF 
>of capacitance, unheard of 30-40 years ago. Back then it was big 
>iron, swinging chokes, smoothing chokes, 4-8 uf of cap, low peak 
>currents, low noise, 

/\  Mercury-vapor rectifier hash is hardly low-noise.  
Ozone is not healthy for humans to breathe.  

>and fairly good regulation with load changes (as 
>long as a resonance wasn't hit during modulation). Resonant input 
>chokes were good here also.

/\  Resonant chokes are undoubtedly the best thing when load current 
swings.  However, swinging chokes are not - but few realize this unless 
they have:  a DC o'scope, a HV o'scope probe, and a  stong curiousity.  I 
plead guilty your honor.  
>I have heard that some of those old CT secondary transformers can't 
>run FWB at full tilt without risking punch through near the center of 
>the winding.

/\  The UTC S-type were infamous for this gripe.  
>Another observation:
>I thought that iron was going to be hard to come by. Two local 
>surplus junkyards had more than I could hope for, anything from 1500 
>to 3500 VDC, single and three phase, 0.2 to 1 Amp DC.  To top it off, 
>I now have THREE plate modulation transformers, all variable tapped, 
>from 300 to 600 W capability. All this for about a hundred dollars. A 
>pair of 813 beam power tubes will be modulators, running AB1.
>This is the fun stuff in ham radio that I had nearly forgotten about. 
>Thanks to this mailing list, I have been inspired to do it.
/\  The main problems with running AM these days is that it wastes watts, 
and virtually all AMers tend to take longish,  "lock to talk" 
transmissions that tend to be a sure-cure for insomnia. 

/\  cheers, John

-  R. L. Measures, 805.386.3734,AG6K,  

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