[Milsurplus] RAK question

[Kenneth G. Gordon]

On 25 Dec 2017 at 22:07, Joe Connor wrote:

> Ken, is the ballast the 38274, the 38593 or the 38276?

Ah. Your tubes are using the old Navy designation: the 38274 is the 874, the voltage 
regulator for the detector, and must stay in there. The 874 is quite a large tube for being a 
simple VR tube.

The 38593 is the 5Z3 four-pin rectifier tube and also must remain in there. 

The 38276 is an 876 and is the ballast tube. It is quite tall, and has a long filament in it. It 
also has a mogul screw base like a big light bulb. It is surrounded on three sides by a 
reflective piece of metal. You must both unscrew that tube, and operate the switch in there 
which bypasses it.

> Do I have to rewire 
> anything to take it out of the circuit or just remove it?

No. No rewiring necessary at all.

As I said, there is a switch in the power supply which bypasses the ballast tube. As I 
remember it, the switch is under the ballast tube, but I am not sure, no longer having any 
original power supplies. You do not have to do any rewiring. The power supply is all set up 
so you can simply switch the ballast tube out of the circuit.

Both Al and I recommend completely removing the ballast tube since even when it is 
switched out of the circuit, it still remains "heated", uses unnecessary power and causes 
unnecessary heat.

If you can't find the switch, let me know and I will dig out one of my old RAK/RAL manuals 
and will look it up so I can tell you exactly where it is. 

You DO have to remove the power supply from its case to get to the switch. You will have to 
loosen the two clamps which hold the input and output cables in place on the back, then 
loosen the thumb-screws on the front. Then the power supply will slide right out of the case.

Once you get it out, and find the ballast tube (it is in the center), and find the switch, the rest 
is easy. The ballast tube is the biggest tube, by a long ways, in there.

For my own RAL and RAK, I use some "shop-made" power supplies which although far 
smaller, provide all the voltages, both regulated and non-regulated, and currents necessary. 
These are built in "mini-boxes" about  3" X 4" X 6". They use solid-state rectifiers, excellent 
filtering, and a VR-90 to provide regulated voltage to the detector, just like the original 
supplies. I did not design or build them: I got them with all the other stuff in the estate an old 
employer left me.

If I can help in any other way, do not hesitate to ask.

Ken W7EKB

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