[600MRG] (Fwd) Re: RAKs and such - ballast tube.

[Kenneth G. Gordon]

Todd is correct, and I am wrong. You RAK/RAL users, please read this.

Ken W7EKB
------- Forwarded message follows -------
Subject:	Re: [600MRG] RAKs and such - ballast tube.
Date sent:	Tue, 4 Nov 2014 02:37:06 -0500


Hi Ken, 

The RAK receivers are a lot of fun to work on. You actually do have to 
remove the #876 ballast tube in the RAK original power supply if you want to 
remove it from the circuit and let everything run cooler.  

When the ballast tube is switched "in" using the internal switch, it is placed in 
series with a transformer winding. The ballast tube is also connected in 
series with a giant 80 ohm/200 watt  wire-wound power resistor R201 across 
part of the transformer windings. It is this combination that causes the power 
supply to draw approx 200 watts. The ballast tube is always in series with 
this big power resistor.  When the internal switch is switched "out" the ballast 
tube is actually still in circuit - this time it is connected in parallel with more 
transformer primary windings but still connected in series with the large 
wire-wound power resistor. This stops the regulation but the power supply is 
still drawing nearly 200 watts.  

You have to physically remove and unscrew the ballast tube from the mogul 
socket to remove the tube completely from the circuit and position the 
internal switch to "out". This removes the large wire-wound resistor R201 
from the circuit also. Doing this drops the power supply input draw to approx 
60 watts.  

Look at the power supply schematic and this action should be clear. A lot of 
the excess heat and power draw when using the ballast tube is drawn by the 
large power resistor R201 always in series with the ballast tube.   

So it is always best to completely remove the ballast tube and remember to 
set the internal power supply switch to "out" to save on excess heat and 
power draw, if someone wants to use the original unit.  

Copy and paste the following address to see the power supply schematic.  

73 Todd WD4NGG  

http://www.navy-radio.com/rcvrs/ral-ps.htm  

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