[600MRG] RAKs and such - ballast tube.

[Bill Cromwell]

Thanks Ken,

I am the one that pointed to battle conditions aboard a warship. Now I 
can see how somebody might wonder if that thing provided star-wars type 
shields or operated a death ray. Mechanical shock - taking a hit or 
firing the big guns - can make the AC line voltage wobble and battle 
damage might include damage to the electrical system. Look what happens 
to your shoulder when firing a mere shotgun. So it really does help 
during a battle - keeps the radio alive.

73,

Bill  KU8H



On 11/04/2014 12:32 AM, Kenneth G. Gordon wrote:
> 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
>
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