Newcomb EDT-29
I found this Newcomb EDT-29 MV turntable at a flea market and as soon as I saw the color inside, I bought it. I see a lot of old AV equipment from schools but nothing ever looked as cool as this. The mustard yellow and fake wood grain are an unbeatable combo and it just feels like a rugged piece of equipment when you pick it up. When I found it, it was not in great shape. The tonearm lock was missing along with 2 feet, it didn't make any sound, and the power was intermittent. Cosmetically it was doing pretty good other than a couple scratches so I was determined to restore its function to match its looks.
I started with the tonearm rest. You can see here where the piece broke off that used to lock the tonearm in place. I found some pictures of the same model to get an idea of what the original looked like. The plastic extended to accept a thumbscrew that could be tightened to pinch the wall of the headshell, holding it in place.
My solution was a piece of steel bent to match the angle of the plastic channel and epoxied in place. I tapped it and threaded an M4 thumb screw in. The steel was blued to keep the rust away.
The notch on the right side of the tone arm wall is where the lock engages.
Decided to keep the school district stickers because I just learned the word
provenance
Surprisingly, the rubber drive wheel was in great shape. You can tell the speed selector is a leftover from the previous era of design. It looks pretty out of place against that mustard chassis. I removed all the old grease and re-applied some fresh stuff to the whole mechanism. That lightbulb in front strobes with the 60Hz against a pattern on the platter to ensure acccurate speed.
Each row of dots is for a different speed setting.
When the record is moving, speed is adjusted until the corresponding dot pattern syncs up with the strobe.
As the speed adjustment knob is turned, a mechanical linkage shifts the position of a magnet in relation to an aluminum disc that is coupled to the motor shaft. It's an eddy current brake controling the speed!
I was delighted to find that the feet I assumed had gone missing were rattling around inside the cabinet broken but not lost.
After a very complicated glue-up, the feet were back in business. On to the electronics...
All carbon comp resistors and axial electrolytics. Some might be able to smell this picture.
The first thing I noticed was this leaking cap. I tested its ESR and it was wide open.
I spent a long time tracing out the circuit for no real reason other than curiosity. A permanent marker is a huge help when tracing a board like this.
And ultimately realized that I wasted my time when I looked inside the cabinet and saw a full schematic complete with test voltages. Oh well.
I went ahead and replaced all the crusty electrolytics (including the one still on the board in this picture)
In case anyone is curious about the transistors, here's one of them. It's not very common to see a speed nut used to hold down a TO-220 device so that's pretty cool.
Also notable is this wierdo longneck pot. Glad I didn't have to replace it.
When inspecting the speaker, I found that the baffle suspended with springs to decouple it from the cabinet and avoid feedback.
Old-school alnico magnet speaker
Next, I installed a bluetooth module and put together a power supply board for it
The power supply is an L7805 regulator and a DC-DC converter IC with some external filtering to isolate the circuit and avoid ground loops.
The bluetooth board is a standard module that I held in place with a cable tie. and the switch below took the place of a microphone input. It switches between bluetooth and the turntable.
And that was pretty much it. It's a great little music player for outdoor listening and it can play records too.