[Amps] ALC Overshoot FTDX-5000

[Jim Thomson]

Date: Mon, 13 Aug 2012 21:12:51 -0400
From: "Joe Subich, W4TV" <lists at subich.com>
Subject: Re: [Amps] ALC Overshoot FTDX-5000

What is the time constant of the Powermaster? Then only clear way to
measure the sub 5 ms spikes is with a scope.

73,

... Joe, W4TV

##  I should try the scope.   I have 4 of the power master watt meter’s
and any of them will  easily show the 3%  ripple of any of my 4 x Drake L4B
power supply’s.   With any cxr over 700 watts, and when slowly increasing the 
PO control on the MK-V  or 1000D,  each bar on the bar graph  would slowly
light up. Then when fully lit up, the next bar would slowly light up, and so on and so on.


##  slam it with a 1200 w cxr.... and sure it sez 1200w  on the digital...Numerical  display,
but the last  segment  was.. dithering.  It was not on solid nor  off, it was pulsing ! 

##  I hooked up my old yaesu scope and  instead of a solid green bar... it wavy on top and 
bottom.  I could clearly see the ripple on the HV  supply.    8 x 200 uf caps. 

##  with amp off... and 1000-D  xcvr cranked to 290 watts out, and scope padding
changed so full height display with 290 w, I get a flat bar on the scope. 

##  replaced caps with higher value ones and  ripple vanished on the scope..... and
no more dithering  segments on the power master display units. 

##  IF your xcvr does have gross amounts of overshoot, the cheap and easy way to fix
that is to just put 9 v dc across a 50 k pot.... and feed the  NEG output  to the ALC jack on the
xcvr.  Set po on xcvr for max.  Tweak 50 k pot  for desired PO.   No more overshoots.
The –3  to –6 vdc   from the 50 k pot is fed directly into the alc jack... and sits there at all times,
rx and tx.  You don’t have to develop alc voltage in the normal fashion.  End of overshoot problem.   

Jim  VE7RF