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[AMPS] info on power supplies

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Subject: [AMPS] info on power supplies
From: (John T. M. Lyles)
Date: Thu, 12 Jul 2001 09:32:47 -0600
I'm building a 'retro' transmitter for high quality amplitude 
modulation. 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, and fairly good regulation with load changes (as 
long as a resonance wasn't hit during modulation). Resonant input 
chokes were good here also.

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.

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.

If anyone needs plate iron, I got the place. Its a little rusty though.



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