This i'ble will take you though the restoration of a vintage tube radio to near-original condition and in the process, upgrade it to play to MP3s with a low cost, easy to build AM transmitter.
This project does not rely on making permanent changes or modifications beyond cosmetic repair and is a great way to introduce novice electrical, radio, or woodworking enthusiasts to what was once the entertainment equivalent of a 60-inch LCD TV.
The model used in this rebuild is a 1936/1937 Emerson AL130 purchased on eBay for less than $60 with restoration/upgrade components rounding out to around $150 (includes Priority shipping).
Manufacturer/Brand: Emerson Radio & Phonograph Corp., New York, NY
Country: United States of America (USA)
Type: Radio / Tuner
Valves / Tubes: 5 total (6A7, 6D6, 6Q7, 25L6, 25Z5) + Balast
Audio: Principle Super-Heterodyne (Super in general); IF-Freq 456 kHz; 2 AF stage(s)
Band: Tuned circuits 6 AM circuit(s), Wave bands Broadcast (MW), Police, sometimes also early TV (75-200m).
Power type and voltage: AC/DC-set / 105-125 Volt
Speaker: Loudspeaker Electro Magnetic Dynamic LS (moving-coil with field excitation coil) / Ø 5.5 inch = 14 cm
Material: Wood case (Ingraham Cabinet, Bristol, CT)
Shape: Tablemodel, Mantel/Midget/Compact but not a Portable (See power data. Sometimes with handle but for mains only).
Notes: BC(540-1580kHz) and TROP(1580-4200kHz) bands. Uses 49 volt ballast tube.
Step 1: Finding a Donor
The first step is to dig around the innerwebs and look at some of the styles manufactured during different periods, taking note of the frequencies they operate in. The most common bands are AM, FM, ShortWave, and Police. Actually playing The Police through your radio is optional, but highly recommended.
Once you get a general idea of what size/shape/era you like, research a few makes/models to determine the rarity of parts in the event your radio is missing components.
DO NOT PLUG IT IN YET! Doing so without giving it a look through for short circuits, bad wiring, or living things (not a joke) may be the last thing you do in this world or at the least, justify nasty looks and name-calling from your local firefighter.
In our example, the AL130 is quite common in that it only needs 5 tubes a balast, and a few capacitors. This is commonly known as an "All American 5" (AA5) design and makes parts easy to track down through various online suppliers.
The following links proved indispensable during the course of this project...
Step 2: Tools/Parts List
[:] Wire strippers, diagonal cutters, needle nose pliers
[:] Soldering iron & station (beginner soldering skills)
[:] Solder, flux/paste, solder wick
[:] Heat shrink tubing
[:] Assorted capacitors, resistors, 16 ga. stranded or solid core wire (as needed)
[:] Replacement vacuum tubes (as needed)
[:] Wood stain (optional)
[:] Sandpaper (optional)
[:] Rubbing alcohol
AM Transmitter parts:
[:] MP3 player (the iPod Shuffle later used is ideally suited for random play, like a radio)
-Bonus points for downloading period correct MP3s from http://www.oldtimeradiofans.com
[:] Small project enclosure (not shown here)
[:] Adhesive backed Velcro (hook/loop)
[:] (1) 1Mhz crystal oscillator
[:] (1) 1k ohm-to-8 ohm audio transformer
[:] (1) Small pre-drilled PCB appx 4cm x 4cm
[:] (1) 1/8" audio jack (male) or headphone cord
[:] (1) 9V battery clip
[:] (1) 9V battery
[:] (1) Single Pole, Single Throw (SPST) slide switch w/ 2 screws
[:] (2) Small alligator clips
[:] 20-30cm of 16ga stranded wire
[:] Electrical tape
Step 3: Physical Conditioning
This radio is still in good condition for being 73 years old but, needed TLC on the cabinet (wood case), as well as new vacuum tubes and a top-to-bottom capacitor replacement.
[DISCLAIMER #1] Doug Criner's site (http://enginova.com/Antique_Radios.htm) has an excellent article on the hazards and checks warranted for any kind of radio/electrical restoration. These projects can get you seriously injured or killed if you throw caution to the wind. I'm not going to beat up on it to much, but I strongly recommended that you visit his site and read up on before proceeding any further. Also, common sense dictates that at no point should you lick your soldering iron. Just sayin'... [/DISCLAIMER #1]
The once over
[:] Unplug the radio from the wall and let rest for several hours (overnight is best).
[:] Check resistors for tolerance (+/- 10% is acceptable), wiring, acoustic, and tuning components. Check for cracked or loose solder points. If a lead is broken or not within the spec, replace with new. A worn out .03 cent part is generally not worth the risk of burning your house down. Loose or cracked joints can be cleaned up and re-soldered as necessary, provided the component is still in good condition.
[:] If you need to replace any tubes, now is the time to make a list. Sometimes the tube part number is labeled on the socket, but if yours is blank, a quick Google should fill you in.
AL-130 Tube Data:
ID Type Function
V1 6A7 Converter
V2 6D6 Intermediate Frequency Amplifier
V3 6Q7 Detector-AVC-Audio Frequency Amplifier
V4 25L6-G Beam Power Audio Output
V5 25Z5 Rectifier
R12 2UR-224 Ballast Tube
Step 4: Busting Caps
Apart from those that were heavily abused, most tube radios can be put into working condition by replacing older paper/wax capacitors with new ones of equal or similar value (+/- 20%).
[DISCLAIMER #2] It's important to note though that while a simple cap job willl ensure clean and uninterrupted operation, to reduce the potential for electric shock or component failure (read: house on fire), be sure to take note of the radio's power cord. Is is polarized? If not, replace it with one that is and see if your radio requires an Isolation Transformer. You can learn more by visiting http://radioether.com/blogspot/page/2. [/DISCLAIMER #2]
The following is a list of capacitors used in the AL130.
.025 mf, 400v_______.022 mf, 630v
.020 mf, 400v_______.022 mf, 630v
.010 mf, 400v_______.010 mf, 630v
.020 mf, 200v_______.022 mf, 630v
.1 mf, 200v _________.1 mf, 630v
.05 mf, 200v________.047 mf, 630v
.002 mf, 600v_______.0022mf, 1000v
Dry Electrolytic_______Replaced with
50/30 mf, 150v_______47 & 33mf, 160v
20 mf, 150v__________22 mf, 160
Note 1: You can save some money by purchasing radial leads over axial. Performance is identical.
Note 2: The 50/30 mf, 150v capacitor (big orange cylinder) is not original and was probably added sometime in the 60's/70's. A single 20 mf, 150v is what the unit originally shipped with.
Get it on
[:] Start by clipping off an old capacitor 1-2cm from the solder joint. Do one cap at a time to prevent miswire.
[:] Use a soldering iron to wick away remaining solder so you can remove the 1-2cm wire lead. Check your work to make sure debris hasn't drop into in the chassis or shorted a neighboring component.
[:] Check the value of the new cap against your radio's schematic. You can find most major brand radio diagrams at http://www.nostalgiaair.org/Resources/.
[:] Route the new capacitor and bend the leads to fit, trimming excess. Slip a piece of shrink tube over the new capacitor lead and cut to size leaving 1-2 cm of the cap lead exposed. You can either shrink the tubing now or let the heat from the iron do it when you solder the components together. This step also works for resistors if you came across one that needs to be swapped out.
[:] Line up the new components and solder the joint. If the solder "beads" or doesn't "flow" smoothly, the iron is either not hot enough or the parts are dirty and component ends need to be cleaned. A common trick is to use rubbing alcohol and/or sandpaper.
[:] Once both ends are soldered, double-check your work against the schematic.
[:] Repeat for all paper/wax caps, again, going slow and doing one at a time.
[:] Triple check your work. If everything looks good, turn it on and see if your soldering skills pass. Don't freak out if you don't hear music immediately. Most tube radios need a few seconds to warm up before they generate sound. If after a minute or two you cant tune a station or get nothing but hum and static, troubleshoot tuner issues through the forums at http://www.antiqueradios.com.
Step 5: Get Some Wood
Wooden cabinets for tube radios varied widely--from simple boxes with a knob and a dial to elaborate and ornamental Gothic styling not unlike medieval churches (coincidentally enough, these are known as cathedral radios). Some were made completely out solid hardwoods like walnut, but more often than not they were boxed frames of cheaper wood with exotic veneers (think paper-thin sheets of wood) wrapped and glued to give the same look at a fraction of the price. Veneer is very thin, usually no more than 0.2-0.5mm so care must be taken as to prevent sanding through and creating holes in the finish.
[:] Remove the electrical chassis, faceplate, bezel, knobs, fabric, and glass/plastic dial cover from the cabinet. Tape a piece of cardboard over the speaker cone to protect it while it's put aside and wipe out any dust/debris from the inside of the case. Assuming its intact, you can reuse the fabric grill guard if you're careful removing it. Most of the time the fabric is sandwiched between 2 pieces of cardboard and stabled to the inside.
[:] Prep your work area and sand the surface of the cabinet with 220 grit sandpaper paper only taking enough material off to get through the lacquered finish. Sand with the grain.
[:] Once you start sanding into the veneer, move to a different area and smooth out any high or low spots. Go slowly to protect the veneer. Smooth rough spots with 300-400 grit paper.
[:] Once you're happy with the prep work, it's time to decide how you want to finish it. If you want a color-stained finish, apply per manufacturer's instruction. Minwax is a reliable brand available just about everywhere and very forgiving for those that have never used stain before. Just follow the instructions on the back of the can and remember that it's always easier to add stain, making the finish darker, but harder to lighten it. Go slow and use a little at a time.
[:] Adding a clear coat will protect the finish and give it another half century of life. If you used stain, make sure your clear coat is compatible (i.e. oil vs water based). Apply in several thin layers rather than one or two thick ones. Sand with the grain between coats allowing plenty of time to dry. This is important for two reasons: 1) it will help hide the deeper scratches, and 2) it will prevent the sandpaper from gumming. Use increasingly finer grit paper (400-1000) until you run your finger across the surface and feels glass smooth.
[:] Clean the surface, re-apply paint to pinstriped areas.
[:] Apply reproduction decals (available from multiple vendors on eBay).
[:] Buff with furniture polish.
Step 6: Making the MP3/AM Transmitter
At this stage, your radio should be in good working order and tune in to local AM stations. If not, go back and troubleshoot. Problems can vary widely and no single instructable can cover every possibility. For now, I'm just going to assume you did your homework and got your radio running.
To play MP3s, we need to build a simple AM transmitter. You could go out and buy a tunable model that broadcasts on more that one frequency, but the cheapest I've seen is $92.95 from http://www.sstran.com and it's not very small or nearly as cool as building one from scratch that hides inside a radio. (Even if you did go the "professional" route, it comes as a kit and you still have to solder it together...just a thought)
Now I'd like to think I'm creative enough to build one from scratch, but credit needs to be give where it's due. Sci-toys.com has some really neat electronics projects and this is basically a tweaked copy of what they've already made publicly available. Total cost for the components I used here was around $11.
If you've never soldered before, dont panic. You only need to make 7 connections. This is easily a 1-out-of-10 project; perfect for beginners. This schematic is about as simple as it gets, but if you get stuck, you head over to their site for a complete walk through.
[:] Clip the center leg of the 1k ohm-side on the audio transformer close to the housing and fit it in the PCB, followed by the oscillator. Note the orientation of the oscillator. The lower left or "sharp" corner should be nearest to the 1k ohm side of the transformer.
[:] Flip the PCB over and bend over/solder the component legs to the underside of the board. Make a solder trace from the oscillator to to the 1k ohm lead on the transformer as shown in the diagram (marked 'C').
[:] Cut and strip a few mm of insulation from a ;ength of wire to make the antenna clip. Overall length will vary but you shouldn't need more than 10-15cm. Solder one of the alligator clips to one end and the antenna lead of the oscillator to the other.
[:] Do the same for the ground wire, but solder both the oscillator's ground and the negative (-) 9v battery clip together.
[:] Strip 2 length of wire and make the audio jack leads. If you have an extra pair of cheap headphones, you can take a shortcut here and use a section 10-15cm long. Strip 2-3mm of the end and solder to the 8 ohm side of the audio transformer (marked 'A' and 'B'). It's not necessary, but If you need to, use hot glue to give the joint strength.
[:] Cut a hole into the project housing and mount the SPST slide switch using 2 small screws. Solder the end tab of the switch to the positive (+) 9v lead and the other to the remaining transformer lead (marked 'D') with a small piece of wire.
[:] Now its time to break out the multimeter and check your work. Probe each solder joint for continuity and check for short circuits. If everything looks good, put a small piece of electrical tape over the oscillator to isolate it from the battery's case.
[:] Cut two small notches on the edge of the project box for the antenna, ground, and audio wire exit points. Attach the 9v battery to the battery clip and pack it the plastic enclosure. Tie a knot in the all wires leaving the box so they cant accidentally pull through.
[:] Close the box up and apply one strip of Velcro to the back, and the other to the radio (or wherever you decide to mount the transmitter.
[:] Attach the "Antenna" alligator clip to the radio's antenna, the ground to chassis ground, and plug in the MP3 player.
[:] Tune the radio to AM 1000.
[:] Turn on the MP3 player.
[:] Turn on the transmitter.