| Note: This site and the data it contains have been reposted from an archive of Nolan Lee's original web site by Steve Johnson. |
Nolan's Redneck "Frankenbulbs"
Revision 1.0c by nlee (7/28/98)
Changes added (12/6/98)
Email address changed (1/13/02)
(Cost effective replacements for the early model R-1051 & T-827 type dial lamps)
I've had many requests for a source of replacement dial lamps for the R-1051B and T-827B receivers and transmitters. Originals are very tough to find. From what I've been told, only ONE manufacturer made them, Grimes Aerospace. I've also been told that they are still available from them at a price of $49.00 each. If you'd like to just order new ones, it's the type A9906-1 rated at 28 volts, .04 amps according to the one of the tech manuals I have for the R-1051B. The FSN/NSN of the original bulbs is 6240-00-623-3618. Good luck!
Off and on over the last 18 to 24 months, I've been experimenting with various methods to implement when my supply of new bulbs are finally consumed. I started out by gutting the original bulb assemblies and modifying them to allow me to use modified #327 bulbs. They worked very well, but involved very labor intensive procedures, both initially and anytime that one of the modified #327 bulbs blew.
The next step was gutting the old bulb assembly and drilling and tapping a couple of holes in the knurled base, a threaded 3-56 hole and a plain #59 or #60 hole, installing a grain of wheat bulb and soldering one lead to the threaded shell of the old lamp assembly and running the other lead thru the small hole and securing it under the head of the 3-56 screw. I modified four of the lamp assemblies and played with them for a while. I finally gave up on the grain of wheat bulbs. There wasn't enough light output and bulb life sucked.
The final step was a modification and improvement of the second step. It seems to be the easiest and the best at duplicating the original bulbs. It's outlined below:
My first step is to remove the threaded shell from the old lamp assembly. The method I use for this is to thread it into a holding fixture and then gently and evenly pry, from two sides, against the knurled base using two screwdrivers as levers. This should result in the threaded shell and the old bulb slipping out of the knurled base and black plastic insulating sleeve assembly. For a holding fixture, I use one of the adjustable gear clamps from an R-390A that I've threaded 5/16-24. My first holding fixture was a 5/16-24 hole drilled into a chunk of heavy plastic from a 55 gallon drum. The reason that I used the plastic originally and later the adjustable gear clamp was that the diameter of the threaded shell of the lamp assembly is slightly larger than 5/16-24. The thread pitch is correct though. After I initially thread the hole in the block of plastic, I ran the tap all of the way thru if a few time to slightly open it up a bit. I learned to NOT attempt to shortcut this holding fixture method by holding the threaded shell with pliers or any other tool. It's very thin plated brass and I've found that it will either flat out crush it or it'll distort it, or I'll burr the threads and it won't screw freely into the lamp holder in the radio. If it doesn't thread freely into the lamp holder, it'll twist the leads of the new bulb when you go to install it, and either create a short circuit or an open circuit to the lamp.
Now, when everything goes well, I have two pieces laying in front of me, one is the knurled base and black plastic insulating sleeve assembly and the other is the threaded metal shell with the old lamp glued into it. I like to do the metal shell first since it's the easiest. First I carefully remove the old bulb and the adhesive that they used to secure it in the shell in place without bending or distorting in anyway the threaded metal shell. This was a slow and tedious process involving the use of a jewelers screwdriver, a leather awl and finally, lightly polishing the inside of the threaded metal shell with 600 grit sandpaper rolled into a cylinder.
Next I modify the knurled base and insulator assembly. This involved, first removing little droplets of old adhesive and then removing whatever piece of old lamp lead that still may be attached between the knurled base and the black plastic insulator. I generally grab it with a hemostat as close to the junction of the base and the insulator as I can and twist until it breaks off. If left in there, it could cause a short. Then I LIGHTLY bevel (just enough to break the edge) the inside edge of the black plastic insulator so that the threaded base can be reinstalled later in the process.
Now it's time to drill the knurled base! Because of the small size of the knurled base it wouldn't be practical to attempt to drill it with any type of power tool. I use a hand held pin vise with a #59 or #60 drill bit to drill two holes in the flat "head" of the knurled base from the outside. I space the two holes each about 1/3 of the base diameter in from the edge in a straight line. If the holes aren't positioned properly the bit will go into the insulating spacer. Not good. After the two holes are drilled, using the pinvise I open up one of the small holes to 5/64 of an inch in diameter. If my original placement of the #59 or #60 holes was off, I choose the one the furthers away from the insulator to enlarge to 5/64 of an inch.
<yawn> Still with me? It's time to checkout the replacement bulbs. Thanks to Don (WC4G), who spend hours looking a lamp specifications and getting info faxed to him, I started using the #2187 bulb. It's basically the same as the #387 (long life #327) without a base. It's rated around ten thousand hours life, draws the same current as the original bulbs, but is a little tiny bit dimmer. Since the current requirements are the same, you don't have to juggle the value of the dropping resistor that's in series with the voltage feed to the bulbs. :-) At any rate, I test each bulb for 15 minutes or so at 22.6 volts in hope of catching any defective ones before installing them in the modified lamp assemblies. After I'm finished, I again test each bulb for about 30 minutes before going thru the pain in the ass job of installing them into the radio.
I now slip the #2187 bulb into the threaded metal sleeve with the leads protruding toward the base. Next, I slip ONE lead of the bulb thru the hole in a plastic transistor base spacer. These are those little plastic wafers about 3/16th of an inch in diameter with anywhere from three to four holes thru them that the military seemed to use by the millions. The other lead is bent at a 90 degree angle toward the side of the bulb opposite from the other lead of the bulb BETWEEN the base of the bulb and the plastic transistor spacer base, out over the bottom edge of the threaded metal sleeve and laid over the outside edge of the sleeve over the threads. The purpose of the little plastic wafer is to prevent both leads from the bulb of contacting the inside of the knurled metal base. If it's right, one lead goes thru the plastic wafer and the other lead goes between the bulb base and the wafer.
Next, I slip the straight lead from the bulb that passes thru the hole in the transistor base insulator thru the little #59 or #60 hole in the knurled base. The purpose of the 5/64 inch hole is to allow me to see that the base insulator and the bulb leads are routed properly. Sometimes I use a needle to reposition the plastic wafer thru that hole, too. Now it's time to put it all together.
The tricky part is to slip the knurled base and insulator assembly back onto the threaded sleeve with one bulb lead between the sleeve and and insulator and the other thru the small #59 or #60 hole in the knurled base without crossing any leads or leaving an excessive lead length. It has to be a straight in push, since twisting it will twist the leads. When it's together, there will be a length of lead protruding between the black plastic insulator and the threads of the threaded sleeve that I'll clip off as short as possible and the other lead protruding from the smaller of the two holes in the knurled base. The leads inside the assembled lamp assembly HAVE to be as short as physically possible.
I'm almost done. For a heatsink/holding fixture to hold the lamp assembly for soldering I use an R390A knob that I've taped over the clamp screw access hole and slightly spread the four pedals and filled with water to level with the inside part that the tuning shaft normally goes into. Then I place the reworked lamp assembly bulb first into the R390A tuning shaft hole so that the water covers the black plastic insulator and quickly solder the bulb lead to the little area of the base BETWEEN the two holes.
After it dries out, I compare the resistance values of the frankenbulbs and the unused #2187 bulbs to see if the there are any shorts or opens. If the values look OK, I'll power up each of the reworked lamp assemblies for a half an hour before I put them in a radio.
I've been wanting to experiment with injecting an adhesive into the base of the assembly either thru the 5/64 of an inch hole or along side the bulb to secure the entire mess together. I can see the potential for damaging the reworked assembly if it's overtightened when installed in the radio or used in an environment subjected to vibration.
An update:
Since I posted my original method of rebuilding the dial lamps, almost 6 months ago, I've experimented with a slightly modified version of the above method that will simplify future re-lamping of the modified lamp assemblies. In addition, this decreases the potential problem of twisting the lamp leads when installing the modified lamp assembly by overtightening in when installing them in the receiver. This modification of the original method involves gluing the threaded shell in the black plastic insulator before installing the new 2187 bulb and soldering one lead of the lamp just below the opening of the threaded shell (without getting ANY solder on the threads!) just inside the threaded end rather than securing one of the wire bulb leads between the threaded sleeve and the black plastic insulator. Your milage may vary, and may the force be with you....
I'd enjoy hearing from you if you have a better method or comments on this method, thanks!