Making BC-611 (SCR536) Batteries

The completed box shown sitting on top of one of Robert W. Down's excellent reprints of the BC-611 TM.

The 0.025" sheet aluminium is available from your home improvement centre. If you do a lot of sheet metal work angle snips are easier to use than straight ones, shown is an angle version.

A Sheet Metal Brake is handy if you have them, If you do not have a standard brake then use two pieces of angle aluminium held in a vice. Or use two pieces of hardwood. Make your first bend and then scribe a line for the second bend
 

The end blocks are approximately 1-1/4 wide and are made out of 1/2 inch oak stock. Spend that extra dollar and obtain oak and the project will be very rugged. The end block sizes will vary slightly depending on your bending of the aluminium box to hold the batteries.

Counter sink the inside of the Plus end piece to make it easier to solder the positive wire.
 

Counter sink the aluminium for the flat head screws. This is necessary in order to allow the tray to slide in and out of the radio.

The positive wire is soldered to the cut off  BRASS bolt. Cut off the bolt after you are sure of a solid contact at both ends of the tray. I know its not red, I ran out of red Teflon wire.

Form a piece of  3/4  wide copper around the bottom of the MINUS block or ground connection. It is fitted around the bottom of the oak block and does not have to be insulated from the bottom of aluminium box. The wide copper strap on the Minus portion of the battery holder is necessary in order to assure good contact with the base spring located in the bottom of the radio. This copper strap is the minus connection for your pack and also makes the case of your home brew pack negative.

The copper strap is held in place by a #4 screw on both sides of the end block. Obviously you have to "stagger" the screws or they will collide.
 

WARNING: No one really likes to receive an electrical shock. Remember that the aluminium tray will be at ground potential and that by holding the tray and contacting the brass bolt you will be exposed to 90 volts. Don't do the standard battery "Tongue Test"!

By twisting the wires as shown and apply heat shrink you will have a good "strain relief" system. Hot air shrinks the heat shrink, much better than a match. Borrow your wife's hair dryer!

Insulated tubing for housing the fuse holder. You can always check the status of the fuse as the tubing is clear.

A finishing touch is a small lanyard to pull the box out of the radio for service. The servicing lanyard is located near the PLUS end.

The Power Supply is now ready for the 3885 net at the Hamfest.

Parts List: PVC coupling, two D cells, some wire and mailing tape. Trim the PVC coupling to a length of 1 and 1/2 inches.

The Red and black wires sneak down into the PVC slit to make the soldered contact with the batteries.

The PVC coupling is slit length ways with a hack saw to allow access to the ends of the batteries. Mailing tape is used to secure the assembly and to provide insulation of the wires.
 

I know the batteries are in parallel and there will be some "internal drainage" as one cell will be slightly different in voltage than the other. I measured less than one tenth of a milliamp current draw for a couple of days. Then I got bored with the test, best advice just forget about it. If you lose sleep over the drainage then unhook one wire after the mission.

Re-solder the shaft of the "A" battery contact and spacer to the spring. Since we are dealing with only 1.5 volts a max effort should be made to improve the efficiency of the system, i.e. reduce losses due to poor electrical contact. Solder the area between the actual battery contact and the spacer shaft.