# Episode 243 - Williams DC Coils

**Source:** For Amusement Only EM and Bingo Pinball Podcast  
**Type:** podcast_episode  
**Published:** 2015-11-09  
**Duration:** 10m 30s  
**Beat:** Pinball

**URL:** https://foramusementonly.libsyn.com/episode-243-williams-dc-coils

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## Analysis

Nick Baldridge explains Williams' engineering decision to use DC-powered coils for flippers, pops, and slings in EM pinball machines, contrasting them with AC-powered alternatives. He covers both the practical competitive advantage (consistent force output) and engineering rationale (power distribution efficiency), then details the technical implementation using bridge rectifiers and the subjective differences in gameplay feel between DC and AC machines.

### Key Claims

- [HIGH] Williams implemented DC-powered coils for flippers, pops, and slings starting in the 1960s to provide consistent force output and draw players who preferred the responsive feel over AC machines. — _Nick Baldridge, host of For Amusement Only, discussing the practical and competitive reasons for DC adoption_
- [HIGH] DC coils maintain consistent power output across all activations, while AC coils experience power variation due to the AC cycle's negative phase. — _Nick Baldridge explaining the engineering difference between DC and AC systems_
- [HIGH] Williams used a shared 24-volt transformer winding to power both the main circuit and a dedicated bridge rectifier circuit for DC coils, with separate fusing to protect against shorts. — _Nick Baldridge detailing Williams' implementation approach_
- [HIGH] A failed bridge rectifier can cause fuses to blow randomly whenever the game starts, and partial failures may produce erratic behavior without blowing fuses. — _Nick Baldridge explaining potential failure modes of bridge rectifiers_
- [MEDIUM] Gottlieb implemented a similar DC coil system, but much later than Williams (Williams was doing this in the 1960s). — _Nick Baldridge recalling Gottlieb's timeline; uses 'I seem to recall' qualifying language_
- [MEDIUM] Williams EM machines feel more 'industrial or cold' compared to Bally or Gottlieb machines, potentially due to both mechanism construction and DC-driven coil characteristics. — _Nick Baldridge offering subjective comparison and speculation about factors contributing to feel differences_
- [MEDIUM] DC flippers produce noticeably different gameplay feel than AC flippers, though the difference is less pronounced when both are properly rebuilt and adjusted. — _Nick Baldridge from personal experience playing both types of machines_
- [MEDIUM] AC flippers are more forgiving of mechanical slop, while DC flippers reveal inconsistencies more consistently. — _Nick Baldridge comparing mechanical tolerance and player feedback between systems_

### Notable Quotes

> "If you play a game and the pops react the same way every single time and fling the ball with an equivalent amount of force with every hit, if the flippers hit consistently, powerfully, every single time, are you more likely to put a coin in that or a game where everything is AC?"
> — **Nick Baldridge**, early segment
> _Frames the competitive/practical reason for Williams' DC adoption as a player attraction strategy_

> "Williams EM's feel a lot more industrial or cold than their Bally or Gottlieb counterparts. And partially this is due to how the mechanisms are constructed. But perhaps partially it's due to the DC driven coils which the player interacts with most often."
> — **Nick Baldridge**, late segment
> _Connects technical implementation to subjective player experience and perceived machine personality_

> "If these [diodes] go bad, then not only is it possible that you'll blow a fuse, not even necessarily any time those are activated, but any time they can become active, meaning any time the game is actually started, it can blow that fuse."
> — **Nick Baldridge**, mid segment
> _Explains a critical failure mode that affects troubleshooting and machine reliability_

> "The bridge is separately fused, and if it shorts, then the idea is it takes out the fuse before it takes out coils."
> — **Nick Baldridge**, technical section
> _Describes the protective engineering design philosophy of the DC circuit_

> "Playing with the properly rebuilt set of AC flippers and playing with the rebuilt set of DC flippers, you can certainly tell a difference, but the difference is going to be less noticeable if your flippers have been rebuilt properly."
> — **Nick Baldridge**, conclusion
> _Nuances the DC vs AC debate by acknowledging maintenance as a confounding factor_

### Entities

| Name | Type | Context |
|------|------|---------|
| Nick Baldridge | person | Host of For Amusement Only EM and Bingo Pinball Podcast; author of this episode's technical analysis |
| Credit.Pinball | person | Email listener who submitted the question about Williams DC coils that prompted this episode |
| Williams | company | Classic pinball manufacturer that pioneered DC-powered coils for flippers, pops, and slings in the 1960s |
| Gottlieb | company | Competing pinball manufacturer that later implemented a similar DC coil system |
| Bally | company | Pinball manufacturer whose EM machines are contrasted with Williams machines in terms of feel |
| For Amusement Only | organization | EM and Bingo Pinball Podcast; the show on which this episode aired |

### Topics

- **Primary:** Williams DC coil design and implementation, Bridge rectifier technology in EM machines, Competitive differentiation in EM pinball manufacturing, AC vs DC flipper gameplay and feel
- **Secondary:** Troubleshooting and diagnostic procedures for DC circuits, Power distribution and circuit protection in EM machines, Manufacturer differentiation: Williams vs Bally vs Gottlieb
- **Mentioned:** Mechanical restoration and rebuild best practices

### Sentiment

**Neutral** (0)

### Signals

- **[design_innovation]** Williams pioneered dedicated DC power circuits for critical playfield coils (flippers, pops, slings) using bridge rectifier technology in the 1960s, providing consistent force output as a competitive differentiation. (confidence: high) — Nick Baldridge's detailed technical explanation of Williams' implementation and competitive strategy
- **[historical_signal]** Williams implemented DC coils in the 1960s; Gottlieb adopted similar technology later, establishing a timeline of technical innovation adoption across manufacturers. (confidence: medium) — Nick Baldridge: 'Williams was doing this in the sixties. I seem to recall that Gottlieb did something similar but it was much much later.'
- **[design_philosophy]** Williams' DC implementation was strategically motivated by player appeal—the consistent, powerful response of DC coils was marketed as superior to the variable AC experience to draw players and coin. (confidence: high) — Discussion of practical competitive advantage: 'are you more likely to put a coin in that or a game where everything is AC?'
- **[restoration_signal]** Properly rebuilt DC flippers produce different gameplay feel than AC flippers; mechanical slop is more apparent in DC systems. Maintenance quality affects perceived system differences. (confidence: medium) — Nick Baldridge's personal experience: DC flippers reveal inconsistencies more consistently than AC; 'the difference is going to be less noticeable if your flippers have been rebuilt properly'
- **[product_concern]** Failed or partially failed bridge rectifiers in Williams machines can cause unpredictable fuse blowing and erratic behavior; diagnostics require point-to-point testing outside the circuit. (confidence: high) — Nick Baldridge's technical explanation of failure modes and testing procedures
- **[technology_signal]** Williams' full-wave bridge rectifier design (four diodes in series) became a standard model replicated in modern solid-state games, establishing a design legacy. (confidence: high) — Nick Baldridge: 'this is the same type of bridge rectifier that you see in modern solid state games'
- **[restoration_signal]** Bridge rectifier testing requires removal from circuit and point-to-point diode testing; cannot be diagnosed in-circuit, establishing a specific troubleshooting protocol for EM restoration. (confidence: high) — Nick Baldridge's detailed diagnostic procedure explanation
- **[design_philosophy]** Williams' use of dedicated fusing for the DC rectifier circuit demonstrates defensive engineering—isolation prevents coil damage if the rectifier fails. (confidence: high) — Nick Baldridge: 'The bridge is separately fused, and if it shorts, then the idea is it takes out the fuse before it takes out coils'
- **[gameplay_signal]** Williams EM machines are perceived as more 'industrial or cold' compared to Bally and Gottlieb machines; DC coil characteristics may contribute to this distinctive feel alongside mechanical construction. (confidence: medium) — Nick Baldridge's subjective comparison of machine personalities across manufacturers

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## Transcript

 What's that sound? It's 4 Amusement Only, the EM and Bingo Pinball Podcast. Welcome back to 4 Amusement Only. This is Nicholas Baldridge. I got an email from Credit.Pinball who asks what my thoughts are on why and how Williams went to the D.C. Pops, flippers and slings. Let's start off with the why. There's an engineering reason potentially and there is a practical reason which go hand in hand really. But the practical reason is to draw players in. If you play a game and the pops react the same way every single time and fling the ball with an equivalent amount of force with every single hit, if the flippers hit consistently, powerfully, every single time, are you more likely to put a coin in that or a game where everything is AC Things do not act consistently because of course there's a negative part of the AC cycle and things have less power because of that fact. So it's a competition thing, that's the practical purpose. Now for the engineering purpose, and this is all guesswork, but if you have a machine which is significantly complex Meshandi, and the game code dedicated circuit to drive these high power incredibly important pieces of the system Most of these games were four games in a four game you have four sets of score Reels you have chimes which are driven with three different solenoids you have playfield activity during the Atomicgines era there was a lot of experimentation with gates and special features which were activated by a particular solenoid. And then you have the normal options on the playfield such as flippers and slings and pops. Now, every single one of those coils has to be driven from the 24 volt system, not to mention the score Motor and any relays which are underneath the playfield. So, basically you've got a line and that line has to go to X number of items.salya's salary hayin universitärs wod azai must love You say bolla in illusti previous j.e 6 bor如此 You got elektroniciisladas Arsaland And see пошå test Tell Rehls干 The reason this is necessary is to support multiple spinning discs or multiple graphics Cards or multiple whatever peripheral you can think of. Well, it's the same kind of idea. You have a separate 24 volt circuit that drives these dedicated coils and ensures that they pop with the same amount of force every second. in black tunas and But if you have all of these coils tied together and you start to see a drop in power that able to be transferred quickly to those coils where you expect power to be transferred quickly this is one way to engineer around it Now, let's talk about the how. This is interesting. Williams used the same 24 volt winding on the transformer in order to power the bridge rectifier that it used. Now, the bridge is separately fused, and if it shorts, then the idea is it takes out the fuse before it takes out coils. It also prevents that circuit from feeding back in to the 24 volt line when it should not. The rectifier is a full wave rectifier, meaning that it makes the current that's fed in as smooth as possible before feeding it to the coils. This is done with four diodes which are arranged back to back to back to back, and this is and the same type of bridge rectifier that you see in modern solid state games. Now, if these go bad, then not only is it possible that you'll blow a fuse, not even necessarily any time those are activated, but any time they can become active, meaning any time the game is actually started, it can blow that fuse. The other thing that can happen is really odd, Zip code Firebase, if the bridge is partially failed things are gonna act really weird and it may not actually blow that fuse in order to test a bridge rectifier you have to take it out the circuit and test point-to-point-to-point-to-point to see if any of the diodes are open Once you done this you should know if the bridge is good or bad Now I think this was a pretty darn good idea on Williams part in order to stay competitive with Gottlieb Now I seem to recall that Gottlieb did something similar but it was much much later. Williams was doing this in the sixties. Playinging a DC versus an AC game is certainly markedly different. However playing a Williams game versus any other game is certainly markedly different. and other game is certainly markedly different in feel. As I've mentioned before, Williams EM's feel a lot more industrial or cold than their Bally or Gottlieb counterparts. And partially this is due to how the mechanisms are constructed. But perhaps partially it's due to the DC driven coils which the player interacts with most often. Playinging with the properly rebuilt set of AC flippers and playing with the rebuilt set of DC flippers, you can certainly tell a difference, but the difference is going to be less noticeable if your flippers have been rebuilt properly. Now if there's slop in the mechanism, you'll notice that too, and fairly consistently with the DC flippers. AC flippers are a little more forgiving. But that's all for tonight. I hope I answered your question, Credit.Pinball. Thank you for your submission. My name again is Nicholas Baldridge. You can reach me at 4amusementonlypodcast Atomicas at gmail dot com, or you can call me on the bingos line that's 724-BINGOS-1-724-246-4671. You can listen to us on iTunes, Stitcher, Pocketcasts, ViaRSS, on Facebook, on Twitter at bingopodcast, you can follow me on Instagram at nbaldridge, or you can listen to us on our website which is foramusementonly.libsyn.com. Thank you very much for listening and I'll talk to you next time.

_(Acquisition: groq_whisper, Enrichment: v3)_

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*Exported from Journalist Tool on 2026-04-13 | Item ID: c17b8e36-e8d2-4692-a67a-02cbaa925fe9*