Recently, I bought an old tube style portable phonograph at a garage sale. It is an Emerson model P1907. When I brought it home and powered it up, all I got was loud 60 hz hum and no music from the speakers. The player also had lots of cosmetic damage, such as a broken grille and missing leather papering I decided to fix this record player and restore it, so that is what I will be doing in this instructable. There will be one of my YouTube videos accompanying almost every step to give the reader a visual demonstration of what is being done to the record player. Lets get started!
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Step 1: Diagnosing the Problem
When I bought this record player, there were many problems with it, so the first logical step I took was to disassemble the record player an remove the chassis. the tube warmed up when the record player was turned on, which showed me that the problem wasn't the tube, so I opened up the chassis and started mapping what I saw. By carefully studying all the components and using a multimeter, I was able to completely draw a schematic of what I saw inside the record player. By drawing a schematic, I was able to know where all the components went and how to diagnose the problem. Because all I heard on the speaker was 60 hz hum, I was able to know that the problem was most likely leaky capacitors.
Step 2: Replacing the Capacitors
In old vacuum tube equipment, the capacitors were made of paper wound with wax inside. These capacitors fail after a long time and become leaky, which means their internal resistance raises and it essentially turns from a capacitor into a resistor. This is not good because it causes the dreaded 60 hz hum on the speakers of whatever piece of equipment that contains these capacitors. Luckily, these old leaky capacitors can be changed relatively easily with the right equipment; a soldering gun (In this case, a gun works better than an iron), pliers, and wire strippers. The replacement capacitors can be found in old power supplies for computers, TVs, ect. To change the capacitors, first you need to find them. They are usually medium sizes cylinders with a lead of wire coming out of each end. They also have their value written on the side, this is helpful when finding replacements. The smaller capacitors are nonpolarized caps and can be replaced with film and ceramic capacitors from and old power supply. The larger ones are electrolytic capacitors and they need to be changed out with electrolytic capacitors from old power supplies. Remember, polarity matters with electrolytics. To change the capacitors, desolder or cut the leads of the old capacitor and resolder the new capacitor in place, you might need to use jumper wires because newer capacitors are usually smaller than the old ones.
Step 3: Replacing the Selenium Rectifier
In old electronic devices, there can sometimes be found a device called a selenium rectifier. This component typically looks like a giant red or green heat sink with a lead on each end. The selenium rectifier is a predecessor to the modern silicon diode and is used as such. It works like a modern diode, but has a larger voltage drop. The problem with these old rectifiers is that because of age, their internal resistance rises, making them heat up faster. This is a problem because it lowers the B+ voltage for the amplifier. Another problem is that if the rectifier heats up, it could fail and release toxic selenium smoke. This is bad, yet it can be replaced with a silicon diode. To replace the selenium rectifier with a diode, first, you need to measure the amperage the circuit is drawing. You can then use this with the fact that a silicon rectifier has a drop of 10 volts more than a diode to figure out the resistor value to add in series with the diode. In my case, with a voltage drop of 10 volts and a draw of 65 mA, I used a 150 ohm resistor. Connect this resistor in series with the silicon diode and solder it in place of the silicon rectifier. It should work now and be safer.
Step 4: Building a New Phono Cartridge
After all the electronics were restored and I turned on the record player, no sound came out. This tells me that the problem is with the phono cartridge, the part of the record player that holds the needle and translates it's movement into an electrical signal. Because I had no phono cartridges and I did not want to buy a new one, I had to Macgyver one out of a piezo buzzer from a microwave. You could just buy a cartridge if you want better sound quality, but I made do with what I had. To make the cartridge, I recycled the needle and casing. I then smashed out the old bakelite plastic and the old piezo element. Finally, I installed the new piezo element using a few popsicle stick pieces to get it at the right height. After turning on the phonograph, it worked!
Step 5: Cleaning the Player
The record player was pretty dirty after a few decades of collecting dust, so I had to clean it. It also has some rat feces in it. First, I used an air compressor to blow out all the dust and rat feces, then I used a wet rag to wipe off all the remaining dirt and grime in the case and the bakelite plastic. After this, the record player should be clean.
Step 6: Repairing Cosmetic Damage
Even after the record player was cleaned, there was still some missing leather siding from the player. I covered this with brown duct tape. The burlap grille on the front was ripped, so I replaced it with some new burlap. Refer to the video in the above step for a demonstration on how to replace the burlap grille.
Step 7: Testing!
To test the record player, I set a record inside, and turned on the player. It works very well and looks pretty nice. To see a demonstration, refer to the video 2 steps above. Thanks for reading and good luck!
Disclaimer: Repairing vacuum tube circuits is dangerous! Do not attempt to repair vacuum tube equipment without an adequate knowledge of electronics.