[600MRG] RAKs and such - ballast tube.

[Kenneth G. Gordon]

On 3 Nov 2014 at 23:06, D.J.J. Ring, Jr. wrote:

> What does a ballast tube do?  Does it help during battle?

No. 

In the case of the RAK and RAL, it is a large tube, somewhat taller than an 
813 and about as big around. It has a large (Mogul) screw base like a large 
light bulb.

Inside there is a long iron wire wound back and forth on mica insulators. The 
bulb is filled with hydrogen. The wire is kept at a red heat. It is connected in 
series between the AC input and the input to a special, lower-voltage winding 
of the power transformer.

The combination consitutes a variable resistor in which the resistance varies 
as the voltage input to it rises and falls, thereby keeping the voltage 
"downstream" from the ballast tube at a constant level. As the iron wire heats 
up due to increased line voltage, its resistance falls, and vice versa, thereby 
keeping the output AC voltage constant.

The ballast tube is an AC voltage regulator.

It was used in the RAK/RAL power supply when the receivers were used on 
warships in which the AC line voltage varied badly, like when a large turret 
was swung.

The ballast tube is not needed when the receivers are used in the normal 
home, unless you like a nice foot warmer.

The ballast tube in the RAK/RAL power supply uses something like 200 
watts just to heat it.

Much smaller ballast tubes are used in the R-390A receiver, in the RCA 
SRR-11/12/13 receivers, and in the HRO-60 to regulate the filament voltage 
of the VFOs. THe HRO-60 used a a 4H4. I can't remember the ballast tube 
in the R-390A.

There are many other receivers and transmitters which used various ballast 
tubes for essentially the same purpose: to regulate critical AC voltages.

Does that help?

Now, RCA designed a simple circuit which using specially connected, back 
to back Zeners of the correct ratings, in combination with a resistor of the 
correct ratings, easily replaces the old ballast tubes and does a better job of 
regulating the AC voltage.

Ken W7EKB