Here at Marco Specialties, we get a lot of questions from people asking about coil substitutions. Let’s preface by saying we always recommend replacing a coil with the same part number as the original. Remember, a weak flipper probably won’t be fixed by replacing the coil with a stronger one, and changing to a non-factory recommended coil can cause damage to plastics, drop targets and ramps. Click “Read More” at the top right for more information.
Before jumping to a coil change, be sure you’ve examined the more common causes of a “weak” coil. First, check the integrity of your coil stop and look for loose wires. A plunger that’s been damaged over time or a worn coil sleeve can also cause underperformance. For flaccid flippers, all of these issues can be resolved by installing a flipper rebuild kit. For other mechanisms, consult your game’s manual to determine the necessary replacement part numbers.
With all that being said, there are times when the original part can’t be found. So, how do we find a replacement? There are several things we need to consider to determine the feasibility of using a substitute coil, but the big three are; the wire gauge, the number of windings in the coil, and the bobbin.
The most important thing to match when substituting a coil is resistance. Resistance is determined by the size of the copper wire in the coil (wire gauge), and how many times that wire is wrapped around the coil’s core (number of windings). As a general rule, a smaller wire gauge or more windings means more resistance, and a larger wire gauge or less windings means less resistance. We want to get as close to the resistance of the original coil as we can when selecting a substitute. Keep in mind that less resistance means a stronger coil, but also more wear and tear both electrically and mechanically. We suggest going with a higher resistance when you can’t find an exact match.
Depending on the manufacturer of the game, part numbers can be helpful. When substituting a Wililams or Bally coil, the numbers after the prefix are the wire gauge and number of turns. For example, an AE-23-800 coil is made with 23 AWG (American Wire Gauge) wire, and that wire has been wrapped around the core 800 times.
It gets a little confusing, but a higher numbered AWG is actually a smaller wire. So, a Williams AE-23-800 would contain larger diameter wire than the Williams AE-24-800. For Data East, Sega, and Stern games, AWG and windings are usually listed in the manuals next to the coil part numbers and sometimes on the coils themselves.
If you can’t determine the wire gauge from the available information, you can measure the wire diameter with calipers and determine AWG using a chart.
Once we’ve found a good resistance match, we need to make sure that the substitute coil will fit in the intended mechanism. We can do this by examining the bobbin. The bobbin is the non-conductive core of the coil, it’s what the copper wire is wrapped around. In the old days these were made of cardboard or bakelite, now we use plastic.
Unless you’re dealing with a Williams or Bally (70’s and later) game, you’ll need to measure your bobbin to determine if another coil will fit in that position. For Williams and later Bally games, the letter prefix at the beginning of the part number will give the size and shape of the bobbin. For example, the Williams part number A-21-650 will have the same bobbin as Williams part number A-27-850. We can apply this to 70’s and later Bally coils as well as long as the coils we’re comparing are both Bally coils. This doesn’t mean that those two parts are interchangeable, just that they’ll occupy roughly the same physical space. Be aware that many manufacturer’s part numbers might look similar but the parts themselves won’t be the same size (all Gottlieb coil part numbers begin with “A-” and bobbin sizes run the gamut).
We’ve added many substitute and equivalent coils to the descriptions on our website over the years to help facilitate this process, so you can trust what you find here. There are also some excellent online resources to help you determine whether or not you’ve found a good replacement. For further reading we suggest Pinball Medic’s Electromechanical and Solid State Pinball Solenoid and Coin-Op Game Coil Charts and John Robertson’s Master Cross Reference Chart of Coils for Coin Operated Games.
-Written by Steve Midgette