Steve's Corner - Pickup Maintenance & Replacement
Over the years the Rhodes was produced, the pickups changed physically, but the differences were not electrically significant. Usually the changes were related to improving production, though some were related to improved sound. The major changes were to the bobbin, magnet and mounting bracket. The early pickups had 1-inch long magnets, and the bobbin size and shape was related to this length. They also had coils that used green or red insulated coil wire. These had no protective tape over the coil wire: later versions had clear or white protective tape.
The early models (73-key) were also wired in a different series-parallel grouping. The first 7 in parallel were then wired in series to 6 in parallel, then 6 more, etc. until the last note (7,6,6,6,6,6,...). They had 1"-long magnets that would influence the decay properties of the vibrating tines, so the magnets were changed to 1/2" in length to minimize the decay frequency changes. Around the same time (early 1970's) and as a result of the magnet change, the pickup wiring was changed to the series-parallel grouping of 4,3,3,3,... (first 4 in parallel, then parallel groups of 3 until the last note). This was the configuration for 73-key pianos until production ended in 1985.
The 88-key pianos also had this grouping, but the last notes past #73 were separated into their own section with a capacitor. In other words, the harp was divided starting at the C below the high C (#88). The high-end section of an 88 is series-parallel grouped as 3,2,2,2,1,1,1,1. Some people comment that the 88's sounded different then the 73's: this is true due to the slightly lower output signal of the 88 harp, caused by the different wiring.
The pickups normally don't go bad, but when one is not operational, it is easy to replace (see the list of Parts Suppliers. Sometimes the pickup sounds low or quiet, but in reality the pickup is dead and the adjacent pickups are producing a faint signal. The best way to isolate the bad one is to take a small screwdriver and tap (while the piano is on) the rivet portion of the pickups in the area where the suspected dead one is located. Each good pickup will produce a loud "clank", while the bad one will produce nothing.
The next step is to unsolder the connecting wire. Be careful: too much heat will cause the terminal to melt the nylon bobbin. The connecting wire wraps around the terminal. Heat quickly and gently unwrap. Removing the bracket mounting screw first will help in giving the wire more slack. Inspect the pickup, and if possible, measure it with an ohmmeter. A good pickup, depending on its vintage, will measure somewhere between 170 and 190 ohms. If the pickup measures outside this range, inspect the coil wire where it is attached to the terminals. If it is broken at the rear or coil start location, you will need to obtain a new pickup. If it is broken at the front or coil end location, you can carefully unwrap one turn, rewind the coil wire around the terminal and re-solder. Re-measure the pickup with the ohmmeter: re-install if you get the appropriate reading, otherwise replace it with a new one. When you re-attach the connecting wire, use the simplified version of hooking it up, due to the short amount of wire slack (see top view, below).
Sometimes a pickup can produce what appears to be noise or distortion: this is caused by the magnet being loose inside the bobbin. During manufacturing, the magnet was inserted into the bobbin, then an adhesive was poured into the bobbin to seal any gaps. Sometimes this seal was not successful and allowed the magnet to vibrate along with the note, causing distortion. The best way to find the culprit pickup is to gently tap the pickup coil (while the piano is on) with the eraser end of a pencil and listen to the sound. A noise or "microphonic" kind of sound indicates a loose magnet. The coils are better positioned for this test if the harp is hinged up (vertical). To fix this problem, reverse-hinge the harp or place the harp in a vertical position such that the pickup rivets are pointing down (as best as possible) and the back or bobbin cup is up and accessible. Pour a small amount of thin or viscous glue into the bobbin cup (DUCO cement is perfect and is found in hardware and even grocery stores). Allow the glue to dry and then retest the pickup with the eraser. It should sound the same as a good pickup.
More Info
- Chapter 4: Dimensional Standards and Adjustments
- Chapter 10: Early Design RHODES Pianos - Dimensional Standards and Adjustments