Unfortunately, I discovered that the speaker coil of the SB-600 is open and the speaker is dead. The SB-600 is a station speaker that matches the SB-101 and holds a singe 8 Ohm, 6” x 9” speaker. The radio’s HP-23 power supply also mounts in the cabinet behind the speaker. After tearing it down I found that the wire between the connection terminal and the coil itself was broken – this is where a very fine wire is stuck down to the paper cone with some sort of enamel or lacquer coating. I don’t feel bad about trashing the speaker to find that out. Even if I’d been able to find it right away, I don’t think I’d have had any success trying to expose the wire and solder it back together on top of the very brittle old paper cone. Better to just replace the speaker and hope the judges don’t notice and deduct too many points at the Pebble Beach Concours d’Elegance for ham radio equipment.
6 x 9 speakers are pretty common, mostly used for car audio. Unfortunately most are 4 Ohm impedance, are not sold singly, and are pretty expensive for this application. While cheap, paper cone 8 Ohm speakers were very common fifty years ago, they aren’t now. I do have a couple of 4 Ohm car door speakers, but they’re the wrong size – 4″ x 6″. I tried one and it seemed to work fine on the SB-101, so I went ahead and ordered a new low-end single 6×9 replacement speaker rather than spend weeks trying to source an 8 Ohm speaker at a reasonable price. Ah, the best laid plans…
I wanted to freshen up the paint on this and the SB-101. They’re not in bad shape, but after this much time has passed since they were new the cabinets collect some nicks and scrapes. A fresh coat of paint is not out of line. Will, N5OLA also sells color-matched paint for the Heathkit SB and HW series equipment. He’s got both spray cans and bottles of touch-up paint with brushes in the caps. I ordered a can of each. Of course the spray paint isn’t textured like the original, but I’m not stripping down to bare metal – just spraying a light coat over the existing paint. I figured if it were too glossy I’d “dust” on a couple light coats to knock down the sheen and preserve the original look. I need not have worried; the paint is a perfect match in both color and sheen.
With the paint done, all that remained was to get it all put back together with the new speaker and the power supply mounted in the back. The HW-series paint is a darker, more turquoise green that is a nice match for the speaker grille on the SB-600. I mainly bought that paint to see if it’s the right color to turn my HG-10 VFO into an HG-10B so it matches my HW-16 transceiver (it is and it did), but it matches the SB-600 grille so well I went ahead and shot a coat on that as well. That takes care of the places where the four black screws for the speaker had taken the paint off when they were installed.
Naturally the speaker mounting holes were off a little, and it was just a touch too wide in the 6″ direction to fit the cabinet. A few whacks with a ball-peen hammer to flatten the sheet metal edges took care of the size, and a step drill bit enlarged the holes enough for everything to fit right. Unfortunately, the audio output is too low and distorted for this to work on its own. I ordered some 4 Ohm 10 W resistors. Adding one of those in series with the speaker made things better. Not perfect, but better. If I find a suitable 8 Ohm speaker for a reasonable price, I’m going to replace it (even though that means pulling the HP-23 back out again, which I don’t enjoy).
I had ordered some new replacements for the rubber feet that Heathkit used – sold as “cutting board feet” on Amazon in several different sizes. With the power supply mounted and everything back together, it looks just great. I’m glad I took the time to shoot a fresh coat of paint on it. I even taped off the Heathkit sticker with the model and serial number.
