Emerson 543 Restoration and Cabinet Repair

Emerson Model 543 AC/DC Radio Set by Donald Sentz Fall/Winter 2011

My mom obtained this set for me in Alabama, sometime in the early 1990’s, and shipped it to me. There was a horizontal break in the Bakelite case on the right side, and duct tape residue. The original speaker had been replaced with another one that was not physically fastened to the chassis. It had one of its original knobs but it was missing the shaft mate insert. I found two other knobs in my junk boxes, one brown and one black, that look OK. I repainted the grill and installed a speaker soon after I got the set. I used “Whiteout” to refill the Emerson logo on the enclosure. I did not replace any internal parts except for the electrolytics. The dial calibration was way off and the set would “motorboat” at the low end of the dial. I put the set away, hoping to one day have time to figure out what was wrong and fix it. Right after I retired, in the summer of 2010, I performed a thorough electrical restoration. I changed the speaker yet again, installed all new capacitors and several new resistors. The motorboating and dial calibration issues were due to the I.F. alignment being way off. I realigned the set using my Heathkit SG-8 signal generator and certain radio stations of

known frequency. Since Bakelite is tricky to repair I used a single long strip of clear cellophane tape to temporarily reinforce the break. The set works really great now. It easily picks up KFBK 1530 in Sacramento at night, from our house on west side of Los Angeles. Also KERN-1180 in Bakersfield usually comes in at night pretty good. Here is a photo detail of the replacement speaker mounting. I used the spool from a roll of Teflon plumber’s tape. The speaker magnet fits nicely inside the hub of the spool after stuffing the gap with a piece of screen window weather-strip. I used an Exacto knife to “drill” the mounting holes in the soft plastic spool flange. I used two ceramic standoffs to mount the spool to the original speaker bracket. Finally I installed a stiff wire brace from the top of the spool flange to the speaker bracket.

Chassis View Showing New Parts Installed. During the 2010 work I reverse engineered the circuit to produce the complete schematic shown below and also on the last page of this report.

January 7, 2012- I found and downloaded a scan of the Riders schematic for this set (see next to last page of this report). There are four minor differences between my set’s present wiring and the Rider’s diagram; 

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My set came to me with a 39 ohm resistor installed for R11 instead of the Riders’ 15 ohm 1 watt part. Also, there was no series resistor R10 for my pilot light. It is possible that the original pilot light may have been something other than a #47, and a repairman may have modified the set for a #47 pilot light. During restoration I did not have the Riders diagram, and I could not figure out why someone had apparently wired pin 4 of the 12SQ7 to the AVC line. This appeared to be a “do nothing” connection. Most other sets I have studied tie pin 4 to the cathode, which is also “do nothing”. Absent Rider’s, I chose to connect pin 4 of the 12SQ7 to pin 3 (cathode). I connected the new 250mmF RF bypass capacitor C13 to B-, to be consistent with other sets. Rider’s shows it connected to chassis. It should not matter which way it is connected, since C19 connects any RF signals on B- to chassis. My C19 is .22uF instead of the .02uF of Riders. My set did not have capacitor C9. The original back cover was missing from my set. I suspect that C9 may have been on the original back cover, along with a pair of screw terminals for the external antenna and ground connections.

July 26, 2013- Four days ago I finally attempted to repair the break in the cabinet that I mentioned in the 1st paragraph of this report. I made an adjustable clamp using two wood lath strips, a piece of cushioning foam, two pieces of #12 insulated copper wire, and two machine screws and nuts. I placed the foam underneath the top strip in order to distribute the compression force and protect the top of the cabinet. I aligned the top and bottom edges of the break while tightening the clamp. See Figure 1.

Figure 1: Cabinet Clamped, but the Front, Back and Side Tape Strips not yet applied I used #150 grit sandpaper to roughen up the inside of the cabinet on both sides of the break. I used acetone to wipe the inside of the cabinet on both sides of the break. I attached strips of masking tape to the front and back edges of the cabinet at the break. These tape strips acted as “dams” to prevent the liquid epoxy from flowing over the cabinet edges before it cures. I also applied a strip of clear Scotch tape all along the break, on the outside of the cabinet. The purpose of this strip is to contain any epoxy that seeps into the seam of the break.

For the repair operation I set the cabinet clamp onto two stacks of books as shown in Figure 2 (I took this picture after the repair operation, so the tape strips were already removed, and also I had spread out a newspaper sheet to protect the books and the table top).

Figure 2: Cabinet in Position for Repair Operation I then used an old toothbrush to dab on a lamination of “Liquid Wood” epoxy (Figure 3) layered with seven 3” x 2½” pieces of “Art Paper” that is black on one side and white on the other side. The freshly mixed Liquid Wood is quite runny, so the tape strip “dams” are very important to prevent it from flowing over the cabinet sides.

Figure 3: Abatron LiquidWood Epoxy I applied a total of seven paper layers, spreading epoxy between each layer. I did not apply epoxy to the top side of the last layer. See Figure 4 showing the repair after partial curing.

Figure 4: Partially Cured Repair I removed the three tape strips about an hour after completing the repair operation. If you don’t wait about an hour the epoxy might flow over the edge, but if you wait too long the tapes will stay glued to the cabinet. I used acetone to wipe some epoxy residue off the outside of the cabinet along the seam of the break. After one day of curing in position I placed the cabinet over a 15 watt incandescent light bulb to heat up the repaired area to about 120 degrees or so. This greatly speeds up the curing process. I removed the clamp and reassembled the set after about 10 hours of elevated temperature cure, spread over three days. The repair appears to be very rigid and strong. Figure 5 shows the set after the repair.

Figure 5: Cabinet Repair Completed

THE END