Your Blogmeister’s Desk
Hopefully someone who is both significantly older than me and is or was an electronics engineer can answer my question, because I’ve never been able to get a good answer to it from anyone.
How did record changers know where to land the tonearm?
Here’s what I mean.
Even in today’s vinyl renaissance, turntables are either totally manual or at best semi-automatic, that being, at the end of the vinyl, the tonearm automatically picks itself up and goes home. However, back in the old days, there were these things called automatic record changers. Of course my mother owned one, which was part of a Tonecrest console system, manufactured (I think) in 1968, and she had it and it was still functioning until as late as 1991. You would queue up one or more records of the same size and speed on the spindle between the placeholder arm and an in-out switch on the spindle, (if you were queuing up 45s, you had to put a special large insert over the spindle which mechanically did the same thing), put the thing on automatic, then throw a switch. The first (or only, if you only had one queued) record would fall down onto the turntable, then the tonearm would land at the beginning of the record (hopefully, but I know it was never a perfect proposition), record would play out, and at the end, it would fetch the next record in queue, or if there were no others, the tonearm would go home.
When I was a kid and learning the ins and outs of the thing, I just assumed that the tonearm knew where to land on the record based on whatever speed the turntable was set for. My mother’s Tonecrest had four speeds: 33 1/3 and 45 are the usual, 78 for old records, (she didn’t have any 78s in my lifetime), and 16 2/3, half of the 33 1/3 speed, as there were some audio books on 12 inch LPs that played at half the normal LP speed, as audio fidelity didn’t matter. The advent of the cassette killed that nascent format. Anyway, I just presumed that if you set the machine to 16 or 33, the tonearm would presume it was a 12 inch record and land accordingly; if you set it on 45, it would assume a seven-inch record and land accordingly, and at 78, it would assume it was a 10 inch record and land accordingly.
In 1984, Hardee’s, the burger chain, wonder twin activated with Warner Brothers to advertise the Gremlins movie, by giving you this combination mini story book and record if you paid an extra buck on top of qualifying food purchases. I loved Gremlins, and a Hardee’s was near where we lived at the time, so of course I got my mother to get all five of them. Here was the catch: As you can see, the record was a seven-incher, but it had an LP spindle hole, not a 45 spindle hole, and therefore, it was meant to be played at 33, not 45. When I was playing them on my own toy kiddie record player, that was no big deal, because that was entirely manual. And if I wanted to play it on my mother’s Tonecrest, it had a manual mode. But what if I wanted to do the automatic thing? I had to play it at 33, but it was the size of a 45, and I had just assumed that when set on 33, the tonearm would think a 12 inch record is on the table and land itself there. But if I set it at 45, the tonearm would land in the right place, but it would be playing too fast.
For grins and giggles, I got over myself to give it a try. I queued up one of them, set it to 33, flipped the switch, and bonzai. And I’ll be damned if the thing didn’t land in the right place. Somehow, the sonofabitch knew that only a seven-inch record was on the table, in spite of the speed being set to 33. I repeated it queuing up all five of the Gremlins records, and it nailed it, every time. After doing a little more experimenting queuing up 45s at 33 and 33s at 45, I had no choice but to come to the conclusion that this thing had some sort of uncanny way to know the size of the records that were on its turntable, and landed the tonearm accordingly. Later on, I came to find out that there were some 12 inch records with LP spindle holes cut for 45 rpm, mainly classical recordings, (the outer circumferences of 12 inchers spun at 45 rpm was the best possible audio reproduction mode on vinyl, so of course classical recordings loved that medium), and some long versions and remixes of pop songs.
The only way I was able to trip the Tonecrest up was with a few vanity “vinyl” recordings that were released on paper thin bendable vinyl; for example, I remember getting such a record from Vacation Bible School. It was around nine inches in diameter and 33 rpm. And since they were thin and bendable, they couldn’t be queued up. Didn’t matter anyway, because once I tried to make it play that record automatically, the tonearm went crazy trying to find a place to land, and then returned home. At that point, I presumed that it took regular weight vinyl for the magic to work, and therefore, the way the magic worked had something to do with the way the record pressed down on the turntable; perhaps there were electronics within the table or the rubber mat that talked back to the tonearm telling it how big the record was.
I was able to confirm later that virtually all record changers were able to do this.
Okay, please, someone tell me how it really worked.