Any photos?

http://ipdb.org/machine.cgi?id=3798

Lucky seven isn't a particularly popular game, so having the rare em version doesn't make it worth much. Unless it's in really nice condition you're probably looking at less than $1000, but with rare things like this the price can also vary widely if you happen to find the right buyer, and there's not much of a price history to go off of.

I've always wondered why they bothered producing them once the demand shrunk that much.

I read while researching the late Gottlieb wedgeheads (last EMs to be produced, primarily, Gottliebs) that they kept making them that long to fulfill the orders of operators who wouldn't confidently make the switch yet, and also Gottlieb "T.K.O." (worth thousands upon thousands now) was only shipped to South America supposedly and if I remember correctly they said it was because they were unsure about how the newer generation of games would hold up in shipping or in the climate, I forget, or maybe I'm imagining things and it was all because of the first thing I mentioned.

Most people think it is because they launched their SS pins midway through a production run (which they did, but I don't think something like that went so suddenly to where it was a "surprise" to them), but the above explanation makes sense because all three major companies that released solid-state machines would not necessarily release such a large scale planned thing in the middle of a game run just because "that is when it came to be", it must have been in the works for longer than the game was planned. But maybe it's a factor of both.

It happened all the time during the switch of EM to solid-state. I just realized Gottlieb infact released many titles/versions both at the same time and then even released more EMs after each pair was released so it does stand true to my story of Gottlieb doing both for years, wow, very interesting! So with Gottlieb, it was basically how many they could effectively sell. With Williams (like yours) and Bally, the number likely stopped as soon as the solid-state versions started rolling off the line and they sold whatever was left of the EM games to the little market left still interested in only operating EM games, and I could suspect they were cheaper as well. (2P EM games were made to cater to operators with less money even if you didn't know that, that's why there are two versions of many (but not all) multiplayer EM games, the 4P version was more expensive due to more parts and likely more "deluxe" in terms of the option for more players (and more money))

For instance, Gottlieb made Sinbad (solid-state, 12,000 produced, February of 1978) and Cleopatra (EM, 1,600 produced, March of 1978, then two months LATER in May 1978 they released the two-player EM version Eye Of The Tiger with 730 produced there. So they actually released the solid-state version before not one but BOTH of the EM versions! I didn't know this, really incredible! IF I AM NOT MISTAKEN, Williams and Bally did it more along the lines of what I first described, they did the transistion without looking back (not including a few prototypes made before the end of the EM stage which never had full productions like Aztec solid-state for Williams (10 produced) and Boomerang solid-state for Bally (1 produced)), while Gottlieb ran EMs along solid-state for a while instead of doing such a harsh switch over, frequently even manufacturing and released in the EM version SECOND and possibly designing the game on solid-state technology first! Or perhaps they wanted the solid-states game to have the "first-released spotlight" which is also very possible.

In addition to Cleopatra, Gottlieb ran the following as EM and solid-state with each machine varying in variety, the rarest of a shared title being Charlie's Angels (not including Countdown and Space Walk which had different names), I'm doing this all from memory (then after I will look up and add which of each was made first - that is not from memory):

Gottlieb Dragon 4P SS (October of 78', released FIRST)
Gottlieb Dragon 4P EM (November of 78', released last)

Gottlieb Cleopatra 4P SS (December of '77, released FIRST)
Gottlieb Cleopatra 4P EM (December of '77, released second)
Gottlieb Pyramid 2P EM (February of '78, released third)

Gottlieb Sinbad 4P EM (February of '78, released FIRST)
Gottlieb Sinbad 4P SS (March of '78, released second)
Gottlieb Eye Of The Tiger 2P EM (May of '78, released third)

Gottlieb Solar Ride 4P SS (February of '79, released FIRST)
Gottlieb Solar Ride 4P EM (March of '79, released second)

Gottlieb Charlie's Angels 4P SS (November of '78, released FIRST)
Gottlieb Charlie's Angels 4P EM (February of '79, released second)

Gottlieb Joker Poker 4P SS
Gottlieb Joker Poker 4P EM

Gottlieb Countdown 4P SS
Gottlieb Space Walk 2P EM (Name change, slight backglass-art design change and most of the backglass art itself was "changed" - Last EM Gottlieb produced, possibly only for export out of the country as well)

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Meanwhile, as you can see Williams did the switch and went on with life immediately (no longer going off of memory):

Williams Lucky Seven 2P EM (Released FIRST, makes sense)
Williams Lucky Seven 4P EM (Released second, newer technology, makes sense)

And that is it.

Does not include:

1976 Williams Aztec 4P solid-state prototype (10 produced), released AFTER the EM version as you'd expect
1977 Williams "Jai Alai" (Unknown amount of players, assumably 4 but who knows) was a working solid-state-only prototype (1 produced), Tom Cahill, former service manager for Williams, gave this prototype away to his nephew and college and when they all graduated nobody took it, nobody knows where it is and it probably was destroyed
1977 Williams Grand Prix 4P solid-state prototype (5 produced), released AFTER the EM version as you'd expect

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As for Bally, I remember that they had taken a similar route to Williams and ditched the EM technology nearly as soon as they could (but slower than Williams) and never looked back:

1976 Bally Freedom 4P EM (Released FIRST as you'd expect)
1976 Bally Freedom 4P SS (Released second, newer technology, makes sense)

1976 Bally Night Rider 4P EM (Released FIRST as you'd expect)
1977 Bally Night Rider 4P SS (Released second, newer technology, makes sense)

1976 Bally Black Jack 4P EM (Released FIRST as you'd expect - 11 months before the SS version too, big gap and the distance went in between some of the other titles (all of them were released before the SS version except one, while NONE of them were released before the EM version)
1977 Bally Black Jack 4P SS

1977 Bally Evil Knievel 4P EM (Released FIRST as you'd expect)
1977 Bally Evil Knievel 4P EM (Release second, newer technology, makes sense)

Other prototypes:

Somebody recently found a Bally Quarterback 4P EM converted to 4P solid-state using one-off circuit boards, even under the playfield, the EM backglass has squares cut right down in a straight line (compared to the equally spaced out across the glass EM digit display holes/sections) for the tube displays - this was basically determined to be a Bally prototype by the community rather than an operated conversion which was also fairly frequent to EM games especially in Italy

4P Boomerang EM
2P Flicker EM
4P Boomerang SS Prototype

Doesn't really count but nice to throw in even though it's irrelevant, no prototype solid-state in this equation!:

1976 Bally Star Trip 2P EM (1 produced, never released)
1979 Bally Supersonic 4P SS (different name and all art was redone)

Phew, that's a lot of brain (and IPDB after) to pick at 4 AM. Time for bed! If you have any more questions, tech OR history, feel free to ask and I will try to answer or have fun speculating and discovering new stuff with you at least.

The interesting thing to me about Black Jack is that they made 120 EMs of them in 05/1976. Then they made 4000 Aladdin's Castles 16,000 Capt Fantastic. And 5000 EM Freedoms. And then 1000 EM Quarterbacks. Then 10000 Fireball home editions, 4000 EM Night riders. After that, the finally released their first SS, 1500 Freedoms. Then 7000 SS versions Night Riders. *then* they made 5000 SS versions of Black Jack. So EM Black Jack was cut off well before any SS of any game went into production. Then they went and did a ton of other stuff, multiple EM+SS pairs close together, and a while later thought "hey maybe we should make more Black Jacks". Most other EM/SS pairs you can be pretty sure they planned to do both. I think the EM Black Jack is the earliest version of any commercial SS game?

Ivan, where are you located?
Europe?
Seems likely that most of the EMs produced after Solid State pins were introduced
went to overseas markets and distributors
where they were a little slower to embrace the new technology.