But designers did figure out sometime in the 1930s that the LTA could be minimized by the judicious use of a canted angle where the plane of the reproducer diaphragm does not lie in the line of the tonearm pivot. Only one proper reproducer cant angle is optimum for a given length of tonearm (distance from the needle point to the arm pivot). You will notice that all modern record players with pivoted arms have the pickup canted at such an angle. If you've ever wondered why, this is why.
What difference does LTA error make? Several things are caused by LTA error. The first effect is a lessening of loudness with increasing LTA error. This is most noticeable in acoustic players where the record is doing considerable work in transmitting power up the needle to the diaphragm. This is caused by the axis of maximum modulation sensitivity of the diaphragm not coinciding with the radius of the record along which the needle is moving with the modulation. But of more concern is the increased record wear which is caused by the nominal position of the needle actually twisting with respect to the tangent of the record groove. Increased LTA error causes more twisting of the needle from one radius to another. This can cause the sharp edges of the worn needle to come into contact with the groove walls which will gouge the record and cause more wear. This is particularly a bad situation when using hard jewel-tipped styli. Of lesser importance is the creation of intermodulation distortion caused by increased LTA error.
With specific regard to the original posting here concerning the Capehart G-line phonograph, these later upgraded 16-E changers used the brown pickup head (F-line and later). This changer was the first phonograph design that I am aware of to use the "pantograph" style tonearm which had a unique pivot system that allowed the CANT angle of the pickup head to CHANGE with the record radius. This allowed the LTA error variation to be lowered considerably from that provided by any finite length fixed, pivoted tonearm design. It was a very clever and unique design for its day and it was designed explicitly by Capehart to address the LTA error variation problem. This design was also seen in a few hifi tonearms of the 1950s and was later resurrected in the Garrard Zero-100 stereo turntable in the 1970s. The "zero" in the model designation implied that the LTA error variation was zero degrees. It worked very well.
Another phenomenon which arises from the use of the canted pickup head is the creation of skating force. Having the reproducer or pickup canted on the tonearm results in the drag force imparted to the tonearm thru the frictional drag of the needle in the groove to be NOT along the line to the tonearm pivot. This causes a torque on the tonearm forcing the arm to skate inward toward the center of the record. This is not too much of a problem relative to the high tracking forces used in acoustic players. But it became a significant problem in the early days of stereo LP playback. This skating force causes the stylus to bear with more force on the inner groove wall compared to the force imparted on the outer groove wall. In stereo records, the outer groove wall represents the right channel of the audio, so record listeners noticed more distortion from mistracking in the right channel than in the left. The solution was the introduction of the "anti-skating compensation" which was fitted to all modern high-end stereo record players, starting around 1966 or so (the Dual 1019 and the Garrard Lab 80 were among the first turntables to have this compensation). This compensaton is a mechanism (with weights, magnets, or springs) which imparts a slight outward torque on the tonearm designed to balance out the skating force. As you would expect, the anti-skate force needs to be adjusted to different values to properly compensate for whatever the tracking force is, so you will see these adjustments marked with tracking force numbers on turntables so equipped. It also matters what stylus shape is being used, so anti-skate adjustments are often calibrated for more than one stylus shape.
Doug, I think you are probably concerned with LTA error in old phonos more than I am. As I've mentioned, the most significant problem with LTA in old phonos is the damage to records that can be caused by LTA error. But this isn't so much of a problem when using steel needles since the needle is relatively soft. But, as you say, some early designs have so much LTA error that the players can actually mistrack or skip grooves due to the large skating force that this causes. The wear problem becomes more significant when you are using harder needles such as Tungstones or any of the jewelled styli. Like you, I reserve a special stack of lesser quality records to be played in my old players so that I'm not going to worry too much about record wear from the use of tungsten needles. But as I've said earlier, I don't recommend the use of jewelled needles EVER in these old players, regardless of their LTA error.
Greg Bogantz----- Original Message ----- From: "Douglas Houston" <[email protected]>
To: "Antique Phonograph List" <[email protected]> Sent: Tuesday, July 14, 2009 5:12 PM Subject: Re: [Phono-L] Capehart
Greg: I was waiting for you to address tracking angle. I can't put my finger on it just now, but I recall seeing some mighty goofy tracking angles on some record players. There can be little doubt that the designers of a lot of phonographs had little or no idea what tracking angle is, or if so, what to do about it. A couple of years ago, someone got hold of some Victor field service bulletins, and they told of a product campaign to correct tracking angles, and they gave serial numbers of the Electrolas that needed correction. My Victor 9-18 was in one of those groups. I looked at it, and it appears to be OK now, so possibly, it was retrofitted. One can just imagine what those 5 pound magnetic pickup heads would do to a record!Oh, now one comes up. The RCA Ejector changer. As far as I know, they were all the same, and the tracking error on my RCA 381 is pretty crumby. Unless they changed the pickup arm length, they were bad from beginning to end.[Original Message] From: Greg Bogantz <[email protected]> To: Antique Phonograph List <[email protected]> Date: 7/14/2009 3:25:29 PM Subject: Re: [Phono-L] CapehartJim, you might get more response on your Capehart questions by posting to the Electrola list. Electrola is dedicated to owners of just the kind ofearly electric phonographs that you own: http://groups.yahoo.com/group/electrola/ But I can answer some of your questions. Yes, the early magneticpickups do exhibit considerable "needle talk" compared with modern pickups. But if your pickup has not been rebuilt, it CERTAINLY needs to be. If it isnot rebuilt, the rubber suspension parts have hardened and the lack of compliance with ruin your records in just one play!Yes, you need to find something other than common steel needles for usewith record changers. The Victor Tungstone needles (and similar tungstenwire needles from other manufacturers) were the best choice for changers of this vintage. The electric record players of the mid 1930s up to WWII werenotorious for inducing massive record wear, mostly due to the poorcharacteristics of the electric pickups and the improper needles used with them. In spite of the preponderance of the sapphire so-called "permanent" needles often found with these machines, these needles are the WRONG choice.These early pickups are much too low compliance and track at too high a force to use a hard jewel-tipped needle correctly. I recommend usingtunsten wire needles for ALL of these record players if you want to preserve your records. Unfortunately, nobody makes these needles any longer, so you are faced with the choice of using steel needles and changing them with ever one or two plays (which negates the advantages of owning a record changer),buying tungsten wire needles when you can find them, or making your ownneedles. Since I am a record changer collector and have a number of these old electric players, I make my own tungsten needles. I'm not geared up tomake them in quantity, so it's a tedious process. But they are worth the effort if you really want to use these players.The circuit diagrams for nearly every early consumer electronic productand quite a lot of mechanical repair information concerning the Capehart (and other early) record changers can be found in the Rider's Perpetual Troubleshooting (PPT) Manuals. These manuals were the mainstay of radio repair shops during this period up to WWII when that information business was taken over by Howard W. Sams. (Sams is the place to look for info on most postwar electronics, but they didn't publish anything on prewar models.) You can find the individual PPT manuals offered on eBay (therewere 23 HUGE volumes in total), but the simplest and cheapest source of thisinformation is to buy the scanned and digitized PPT manual collections complete on CD or DVD. These are also offered by several sellers on eBayand can usually be had for $10 or less for the ENTIRE collection. Anothergood source of early record changer info is the Rider's book titled "Automatic Record Changers and Recorders". This was a single volume published in 1941. These also appear often on eBay. Greg Bogantz----- Original Message ----- From: <[email protected]>To: <[email protected]> Sent: Tuesday, July 14, 2009 1:11 PM Subject: [Phono-L] Capehart > After many years, my 1937 Capehart 404G (serial number 10627E) is now > functioning & sounds great & is fun to watch as it changes > records. I have noticed quite a bit of "needle noise" in the magnetic > pickup when the volume is turned down even though the pickup> has been restored. Is this endemic to a properly performing Capehart > as> I suspect because all the doors to the record playing > compartment are sealed with rubber gaskets, presumable to contain > mechanical noise or does the pickup need further work? Also, > where can one obtain needles for playing large numbers of 78s without > being changed in the Capehart or Orthophonic Victrola 1050? > I have Mr. Baumbach's excellent book on the Capeharts without which the > repairman who usually works on 1950s & 1960s hifi gear> would have been completely at sea in working on the Capehart changer > but> would like to obtain copies of the owner's manual & > schematics of the tuner & amplifiers. > > Jim Cartwright > > Immortal Performances > > > [email protected] > _______________________________________________ > Phono-L mailing list > http://phono-l.oldcrank.org _______________________________________________ Phono-L mailing list http://phono-l.oldcrank.org_______________________________________________ Phono-L mailing listhttp://phono-l.oldcrank.org
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