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Grandad's Gramophones
Grandad told Junior, "The way of making
grooves in a material that
represented the sounds to be recorded was invented by Thomas Edison in
1877, long before even I was born. He used tin foil, but, by
1887, cylinders of hard wax
were used, with a groove around the outside running from one end to the
other. Later on, around 1892, a flat disc of material was used by Emile
Berliner. This was better than
a cylinder if lots of copies were needed. Why do you think it was
better?"Junior quickly picked up on that one. "If it's a cylinder, you must copy it by either making a whole new cylinder in the same way as the first one, or somehow play the groove from the first one onto the copy. With a flat disc you could use a reversed image of the first one and press the groove into the copy."
"Yes," said Grandad. "They did work out a way to copy cylinders in that sort of manner, but it was slow, and easy to break the copy. First, after the original, master cylinder was produced, it was plated with metal to make a reverse mould. Then the outside was built up with something to make it stronger, and the original wax cylinder melted out of the mould, which of course destroyed it. Then a special wax was poured into the mould and sloshed about. The special bit was that this wax shrunk when it cooled, so that the copy of the cylinder could be taken out of the mould. But lots of things could go wrong, and it cost a lot to make copies this way."
"I've thought of another thing," said Junior. "On a disc, you have two sides that can be used, but a cylinder has only one side that can be used." He added cleverly "But it still has two sides - an outside and an inside."
"Hmmm," said Grandad. "Not all flat disks had recording on both sides. Sometimes the 'second' side was just left blank. And that reminds me of another advantage of the flat record. It had a bit of space in the centre of each side where a label could be stuck, saying who made the record and so on."
"Did they always make them the same way?" asked Junior.
"In the early part of the 'twenties, the originals, called 'masters', were made using a great big horn, a bit like the one on my gramophone only bigger, to 'catch' the sound. This was used with a special sound-box to cut the groove in the master recording. This was called 'acoustic recording'. Then, after making a mould from the master, the copies for sale were pressed into a blank record, often made of a mixture of shellac and some sort of filler, usually powdered slate, but even wood dust was used, to make the record that was then sold. This was sometimes called a 'pressing' because of how it was made. Then in the later part of the 'twenties, when valve amplifiers were capable of providing enough output, they made 'electrical recordings', using microphones, that had much better sound than the previous 'acoustic' ones. They used better materials for the record itself, such as a plastic called PVC, to be able to make the grooves smaller and closer together."
"When did they stop making them electrically?" asked Junior.
"They didn't, really," replied Grandad. "They didn't stop making them electrically, they just stopped making them at all. That's because the industry started making other things, using different methods, such as Compact Disks that you will know as CDs."
"Yes, I know them," said Junior. "Do they still use microphones for recording them?"
"They certainly do," Grandad told Junior. "Even now they still use microphones to convert sound waves into electrical signals for recording and broadcasting."
Grandad said "You can see my disk gramophone with a
metal horn, and the
other gramophone in a cabinet, where the horn is hidden inside the
cabinet.
Both of these have clockwork motors, that must be wound up before a
record is played. The speed that the spring runs the turntable at is
regulated by a rather clever thing inside, called a 'centrifugal
governor'. Can you see how it works?"
"Not really," replied Junior. "Will you explain it to
me one day,
please?""Yes, of course I will," said Grandad. "Maybe next time you come?"
"Do all gramophones have clockwork motors and horns?" asked Junior.
"Bless you, no," replied Grandad. "One problem with the old horn gramophones was that all the energy, that was needed to make the sound heard, was taken from the groove in the record by a metal needle, which waggled a thin, flat piece of metal or mica called a diaphragm, so that it moved the air next to it. The thing that all this was in is called a 'soundbox'. The back of the diaphragm had a way of being connected through a hollow moving arm into the thin end of the horn. The horn flared out to the fat end, and from there you hear the sound. The horn acted as an acoustic transformer to match the diaphragm to the open space of the room, but the groove of the record had to transfer all the energy. The groove soon got worn, which resulted in the sound getting worse; more noisy and with fewer high notes."
"I don't think that I understand an 'acoustic transformer'," said Junior.
"Never mind," said Grandad, "I don't think I can explain it to you very easily, either."
"Here's another way that the soundbox was
matched to the air, but this time using a reflector rather than a
horn," said Grandad. "It looks very odd, but it is extremely
successful. The tone-arm ends at roughly the focal point of a
hemispherical dish, which then reflects the sound. It's a bit like the
dishes that I've seen on houses for receiving satellite television, but
for sound, and for producing the sound instead of receiving it."This is a DECCA portable gramophone, made by Barnett Samuel & Sons Ltd around 1915. The name was patented in 1914. In 1928, largely because of the success of the Decca, they changed their name to The Decca Gramophone Company Ltd, and eventually became the Decca that you might have heard of even today.
"You can see that this one has a mica
diaphragm in the soundbox. The diaphragm looks a bit different to the
steel ones, doesn't it?""Yes, it is sort of see-through," replied Junior. "Does it sound the same as the steel ones?"
"It has a more brittle, sharp sound than the others," replied Grandad. "And in this Decca gramophone, with it's rather small reflector, it sounds quite harsh."
"What about the clockwork motors?" asked Junior. "Why weren't they electric?"
"Later they were," said Grandad. "Some were made a bit like the clockwork motors, but other designers took advantage of the a.c. mains to make the turntable itself into part of the motor. Look at that turntable; it has two parts. The 'stator' would be fixed to the board of the gramophone, and is powered by the mains. In this case it is designed for mains volts at 50 cycles per second, and still suits the 240 volt mains we have now. In the centre is a ball bearing for the turntable to run in. Around the edge you can see lots of little bent-over 'fingers', which are the pole-pieces. The make a magnetic field that drives the turntable. It is called the 'stator' because it doesn't move; it remains static.
"The turntable is called the 'rotor' because
it is the part that
rotates. It sits over the stator, and can rotate in the bearing. When
it is connected to the mains, it turns at about 79 revolutions a
minute, roughly the
standard speed for old records. Originally there was no
standard speed; every company had their own, but 80 revolutions a
minute was quite common. I suppose it sounded a nice round number.
Later on , 78 revolutions a
minute became standard. With
a mains frequency of 50 cycles a second, that is 3,600 cycles a minute
of course, they get 79 revolutions per
minute, bang in the middle of the normal speeds. How many fingers can
you
count on this motor?"Junior tried counting them. After a while, and after starting several times, he said "There are 76 on the stator and the same on the rotor, Grandad. How does that get the right speed? I expected 78 for a 78 speed record."
Grandad explained "This is called a 'synchronous motor'. Every finger on the stator is a pole-piece, alternating between one end and the other of a flat coil connected to the mains. When it's connected, one pole and it's neighbours will have opposite polarities of magnetism, North or South, depending on the mains, and changing 100 times a second between North and South polarity. In the rotor, the same number of permanent magnets, alternating North and South polarity, get attracted to the opposites and repelled from the same polarities on the stator. To keep in this arrangement, the rotor has to turn around. In this motor, there are 76 pole-pieces being fed with a 100-times-a-second flux changes for a 50 cycles per second mains frequency. If the rotor keeps up with the stator flux changes, how fast will it go?"
Junior took a piece of paper and a pencil.
"Gosh, Grandad, I didn't expect to be doing this sort of thing!" he complained.
Grandad looked at Junior's sums on the paper.
"Well done," he said. "Because we have 50 cyles per second mains, the rotor has to turn at a speed determined by 100 flux changes a second, that's 6000 a minute, and the 76 pole-pieces rotate so that 76 flux-changes will turn the rotor one complete turn. That gives a revolving speed of 6000 changes a minute divided by 76 pole-pieces, just as you have written. Now, let's try to use this twenty-first century calculator - Mmmmm - Aaaaaaah."
"Oh, let me use the calculator," said Junior impatiently.
"O.K." said Grandad. "My fingers are too clumsy for it."
"If you say so," replied Junior, cheekily. "Look, it's easy. The answer is 78.947368 revolutions a minute."
"Shall we call it seventy-nine?" laughed Grandad. "That's close enough!"
Grandad then asked "So how many pole-pairs would be needed to get 78 revolutions per minute?"
Junior thought about it for a while and asked "Is it 6000 divided by 78, Grandad?"
"What does that come to?" asked Grandad.
"It's a funny number, I think," said Junior, "Not a nice round number like 76. It's 76.923077."
"That's nearest to 77, We must have whole numbers of poles!" said Grandad, "We can't have an odd number of poles, or there would be two poles of the same polarity next to one another, and that won't work. So we must choose a close even number, like 76, which is what they made it with. If they had chosen the next higher number, 78, what speed would it have made?"
Junior bashed away at the calculator and came up with the answer.
"It doesn't really matter about the exact speed," said Grandad. "Not many people can distinguish a slight error, and often records weren't even made at the exact correct speed. These days it's all done much more accurately, but most people wouldn't notice if it was a bit wrong, as long as it was constant and didn't vary. That could sound horrible - it even has a name, 'wow' for slow changes and 'flutter' for fast changes."
"Of course, there are other ways of driving the turntable," said Grandad. "Almost all electric turntables use a motor that runs at some handy speed, then use pulleys or friction drives to get exactly the right ratio. Then the number of poles on the motor doesn't matter at all, and you can get any speed just by changing the pulley sizes.
"It's
even possible to have a tapered pulley, like this Goldring-Lenco one,
that
let's you choose any speed in a range, not just from a set of three or
four, by moving the friction wheel to the place you want."Junior had been thinking about other things.
"Why didn't they use a sort of reverse of the electric recording method to make an electric playback?" asked Junior.
"They did," answered Grandad. "It wasn't long before
electric pickups
were available to replace the sounbox and horn. The movement of the
needle waggled a coil of wire within a powerful magnet, or something
similar. This made an
electric signal appear at the ends of the coil of wire, and this could
be fed to a valve amplifier and used to work a loudspeaker.""That must have been much easier on the record, because the amplifier made the sound stronger and the groove of the record didn't have to make all the noise," guessed Junior.
"Eventually it was like that," said Grandad, "But the first sort of electric pickup was rather a monster; very heavy because of the big magnet in it. Even with a balancing spring, lots of this weight pressed down on the record and could damage the groove.
"They used needles made out of thorns for a while -
these were softer than steel needles, and didn't damage the record
quite so much, but worn-away bits of fibre could clog up the groove and
needed cleaning out. These fibre needles could be sharpened and re-used
several times before they got so short that they wouldn't fit any more.
There were even special machines made for sharpening these needles,
that ensured a sharp central point! Later on, they used smaller and
lighter magnets and coils, as
well as other ways of making the movement of the needle generate
electricity."
Grandad showed Junior another old pickup."This one is more modern," he said. "It doesn't have a screw to hold the needle in place, but uses the magnet in the pickup to hold the needle. The head is much lighter, because the magnet is quite small."
"But that won't work with thorn needles, only steel ones," said Junior.
"You're right," Grandad replied, "But most people used steel needles anyway.
"In fact, some needles were made already
magnetised! The makers claimed that these were the only sort of needle
to be used with 'electrically recorded' records.""Were they better than non-magnetic needles, then?" asked Junior.
"Just a clever bit of marketing," replied Grandad. "There's no reason at all why they would be better. They might collect up some of the worn-off metal from out of the record groove, but the chances are that the bits clinging to the needle would do more damage to the groove anyway. Just because a record is made by an electrical process, using a microphone, does not suddenly make magnetised needles the right thing to use! I bet they sold a lot, though. Awful things - they all stuck together in a clump in the packet, all held together by their own magnetism!"
"Did you use them?" asked Junior.
"Well, maybe I did," mumbled Grandad.
Grandad wanted to show Junior another gramophone part.
"This was Grandma's pride and joy," he said.
"It looked pleasant in it's polished case. It's an electric turntable,
just like you asked me about. This one is made by Columbia, who had
also made clockwork gramophones and gramophone needles. It plugs into
the pickup sockets on the wireless."Junior opened the lid to get a better look at the insides.
There wasn't a lot to see, but Junior
noticed that there was an odd metal shape near the turntable.Grandad explained that, with this deck, you started the motor by pulling the pickup outwards, away from the turntable, and stopped it by moving the pickup in towards the spindle. That way, it stopped automatically at the end of a record.
"It has a whopping big pickup head to it!" he exclaimed. "When I lift it, it seems to weigh a ton!"
"Maybe not quite that much," replied
Grandad, "But it is pretty heavy. This is the sort of pickup that
chewed up records in no time. They seem even heavier than the old
acoustic pickups, because of the big magnet inside, I suppose."Junior noticed something else.
"Grandad, the mains plug is strange. It hasn't got any pins, and it's round," he remarked.
"That's a light-bulb adapter," said Grandad,
"It is like the bayonet base of a light bulb. Many people didn't have
any wall sockets in their rooms, just light bulbs hanging from the
ceiling. You could get a two- or three-way adapter that plugged into
the bulb socket; the bulb went into the straight part of it and one of
these adapter plugs into the side socket. I've got one somewhere.
Then power came through if the light was turned on. The cable hanging
down from the ceiling was not very good, but we managed to tie it to
the picture rail so that it wasn't too bad.""They're a good idea!" said Junior, "I could use one in my bedroom."
"No," replied Grandad. "They're too dangerous and are illegal now."
Junior, of course, wanted to see the works of the deck, and Grandad seemed eager as well. He turned the whole case upside down and unscrewed the bottom cover. Then he remembered that they hadn't seen the top without the turntable on and turned it back the right way. He lifted off the turntable and they looked at the stuff under it.
"I can see a motor that looks very like the
one on the modern Lenco deck," said Junior."You certainly can," said Grandad, "This motor is not like the synchronous one that we saw earlier, but is rather like the Lenco one. It is a shaded pole induction motor, that runs at just about the right speed, not exactly constant, but no worse than a clockwork motor. It drives the turntable spindle through a gearbox, to get the right speed. Of course, unlike the Lenco deck it can only manage one speed, which is 78 RPM. That was the only speed you needed in those years, because lower speed plastic records were not yet invented. Modern plastics like PVC were a thing of the future!"
"Anyway," said Junior, "It looks as if that humungous pickup would make mincemeat of a 45."
"What does 'humungous' mean?" asked Grandad. Junior explained.
They turned the case over then. Grandad had already removed the baseplate.
"There's the motor and gearbox," said
Grandad. "You can see the mains wiring and on-off switch quite clearly.
The links to the left of the switch are to connect the motor windings
for either series operation for 250 volt mains, or for parallel
operation on 120 volt mains.""Who has 120 volt mains?" asked Junior.
"It's close to the American voltage," replied Grandad.
"But isn't their mains 60 cycles?" asked Junior. "Wouldn't that make the motor run too fast?"
"Sixty cycles a second," corrected Grandad. He was pleased that Junior had realised that the motor would run too fast, but didn't want to admit that he hadn't though of it himself.
"In later years things changed a bit more," Grandad said. "People wanted the players to be self-contained, with their own amplifier and speaker. This way they could play records in places where there was no radio to amplify the signal. Some used batteries, but most needed a mains supply."
Junior was interested. He had a complicated setup in his bedroom at home, and he could easily think of why younger people might want a more portable record player!
"Why didn't they do that earlier?" he asked.
"The cost of the amplifier and speaker was too high for most people," said Grandad. "Some people bought radios that had gramophone decks built into them, so that they didn't need two items. These were known as 'radiograms'. We never used to have one of these; we always used the separate turntable plugged into the wireless, until more recently."
Junior was a bit surprised. Grandad always seemed to have everything. Junior had even seen Grandad's radiogram, which Grandma and Grandad still used!
When your Dad was younger, I made him a self-contained gramophone," he said. "They were called 'record players' for some reason. I suppose they did only play records, but there was already a good name. Just as bad as calling the wireless a 'radio'."
Junior didn't rise to the bait, but waited patiently. Grandad seemed a bit disappointed.
Grandad pointed to an odd-looking box nearby, covered with red covering except on the front part, where the covering was green. Right at the front two cream-coloured knobs stood out from a silvery grille.
"I made this out of bits and pieces," said Grandad. "The covering is called Rexine. Grandma had some odd bits left over; just enough to do it like that, in the two colours."
"It's really rather nice," said Junior, interested in looking inside and not wanting to upset Grandad.
"What's inside?"
Grandad opened up the lid. Inside was a record deck
like some that
Junior had seen somewhere. There was a pick-up arm that could be
moved over the record, which sat on a turntable.Grandad said "This is a really modern record player. It uses a BSR record deck from 1956, with a turnover cartridge to let it play real records and those modern little plastic ones with the tiny grooves."
"Let me see," said Junior, "the front of the pickup has a little knob thing that lets it be turned over. On one side it says '78' and on the other '33-45'. What does it do?"
"With old records that turn at 78 revolutions a minute, called 78 rpm, the grooves are nice and wide, so you need a big stylus", said Grandad. "Those plastic ones that turn at 33 or 45 rpm have fiddly little grooves, so by turning the knob on the pickup you select either the big or little stylus."
"Is a stylus the same as a needle?" asked Junior
"Yes, it does the same job," replied Grandad, "It is really the modern name. Usually a stylus is made of a really hard material, like sapphire or diamond, and it doesn't wear away at all quickly. The longer it keeps the right shape, the less it damages the record."
"Grandad, why is there a d'oily on the turntable instead of a rubber or green cloth mat?" asked Junior.
Grandad laughed. "The old rubber mat went as hard as a board, and curled up along one side," he said.
"Grandma offered to knit me one, so I let her make this one. Good, isn't it!"
Junior didn't like to say anything, just in case he upset Grandad and Grandma. He just nodded.
"Does this one have a pick-up with a big magnet in it?" asked Junior.
"No, this uses one of the other ways," replied Grandad. "This has a 'crystal' pickup. It's the same as a crystal ball; it looks into the future and know what sound is coming", he joked. Junior didn't realise it was a joke at first.
"But really
It is a small bar of a
chemical crystal. Often they use stuff called rochelle salt. When
this bar is bent, it generates electricity, so by joining the stylus to
it,
it will make an electric copy of the sound written into the groove of
the record. This one still works, but doesn't produce as much
electricity as a new one would. We say that it has lost 'sensitivity'.
This can happen for many reasons, but most common is that it gets damp
and partly dissolves, like sugar in tea."That reminds me, where is that cup of tea I've been waiting for?"
After Grandad had drunk his tea, Junior wanted to know more about the record player.
"Show me where the electrical signal from the rochelle salt gets amplified such that we can hear it," he demanded.
Grandad lifted out the board that held the turntable.
"There," he said, "That's the amplifier. It has two
small valves in it.
One of them is called a rectifier; it turns the a.c. from the mains
into the d.c. needed to work the amplifier. The other valve is a
'two-in-one' valve that amplifies the signal from the pick-up and makes
it strong enough to drive the loudspeaker so that we can hear it. This
valve is called a triode-pentode, because one part is a triode and the
other is a pentode. I'll tell you more about that another time.""This thing next door to the amplifier is the loudspeaker. This one is called 'elliptical' because of the shape of the cone, but often round shaped cones are used. The amplified electrical signal feeds a coil of wire that is joined to the paper cone. A powerful magnet around the coil makes it behave like a motor, so when the signal changes the coil moves and, in it's turn, moves the cone. This sucks and blows the air and makes the air movements that we hear as sounds."
"I wanted to show you a record player and radio combined, called a radiogram," said Grandad.
"OK, Grandad," said Junior.
They went into the sitting room and Grandad talked about radiograms and showed Junior one.
Junior said "I think I know enough about gramophones and record players for now, thank-you Grandad."
"Well," said Grandad, "Shall we have a practical test?"
With that he produced an old record and played it on all the gramophones one after the other. They all sounded different. He seemed to be enjoying it.
"What's it called?" asked Junior.
"The Teddy Bears Picnic, sung by Val Rosing with the Henry Hall orchestra," answered Grandad. "Believe it or not, this record was often used by sound engineers for checking their setups, because it has wide amplitude and frequency ranges! But I just like it."
"I like it too," said Junior, "But doesn't the singer sound posh!"