[Phono-L] Capehart

Tue Jul 14 20:13:32 PDT 2009

    Doug, you are right that the early disc phonograph designers didn't have 
much of a clue about lateral tracking angle (LTA).  This is the angle formed 
between the axis of modulation in the pickup (the perpendicular to the plane 
of the diaphragm in an acoustic reproducer) and the radius of the record at 
the point where the needle contacts the record.  Ideally, this angle should 
be 0 degrees at all music radii of the record.  (Sometimes you will see this 
angle described as 90 degrees in which case the reference is to the plane of 
the diaphragm instead of to the normal to that plane.  "LTA error" is still 
the deviation from the optimum, regardless of the definition of the 
reference.)  One of the inherent problems of designing a pivoted tonearm (a 
single lateral pivot point located at a finite distance from the center of 
the record) is that the lateral tracking angle will NEVER be constant at all 
record diameters.  The variation in LTA at different radii is often 
described as the LTA error variation.  Note that if you change the distance 
of the pivot of any given tonearm from the center of the record, the LTA 
changes.  What is much less obvious without careful inspection is that there 
is one or at most two places along the music radii where the LTA error can 
be made to be exactly zero degrees with proper design of the tonearm.  The 
use of a longer tonearm reduces the amount of LTA error variation along the 
range of radii, and in the limiting condition of an infinitely long arm, the 
LTA error variation goes to zero at all radii. Consequently, the LTA error 
problem can be eliminated by the use of a linear-tracking tonearm 
arrangement (which simulates an infinitely long pivoted arm) such as is used 
on most cylinder players and in some modern stereo LP players.  (Note that 
even with an infinitely long tonearm or a linear-tracking arm, if the stylus 
position is not correct, the LTA can still be non-zero.  In this case, both 
the ERROR and the ERROR VARIATION will be non-zero at all music radii.)

    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" <cdh041 at earthlink.net>
To: "Antique Phonograph List" <phono-l at oldcrank.org>
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 <gbogantz1 at charter.net>
>> To: Antique Phonograph List <phono-l at oldcrank.org>
>> Date: 7/14/2009 3:25:29 PM
>> Subject: Re: [Phono-L] Capehart
>>
>>     Jim,  you might get more response on your Capehart questions by 
>> posting
>> to the Electrola list.  Electrola is dedicated to owners of just the kind 
>> of
>> early electric phonographs that you own:
>>
>> http://groups.yahoo.com/group/electrola/
>>
>>     But I can answer some of your questions.  Yes, the early magnetic
>> pickups do exhibit considerable "needle talk" compared with modern 
>> pickups.
>> But if your pickup has not been rebuilt, it CERTAINLY needs to be.  If it 
>> is
>> not 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 
>> use
>> with record changers.  The Victor Tungstone needles (and similar tungsten
>> wire needles from other manufacturers) were the best choice for changers 
>> of
>> this vintage.  The electric record players of the mid 1930s up to WWII 
>> were
>> notorious for inducing massive record wear, mostly due to the poor
>> characteristics 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 using
>> tunsten 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 own
>> needles.  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 
>> to
>> make 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 
>> product
>> and 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 (there
>> were 23 HUGE volumes in total), but the simplest and cheapest source of 
>> this
>> information is to buy the scanned and digitized PPT manual collections
>> complete on CD or DVD.  These are also offered by several sellers on eBay
>> and can usually be had for $10 or less for the ENTIRE collection. 
>> Another
>> good 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: <jimcip at earthlink.net>
>> To: <Phono-L at oldcrank.org>
>> 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
>> >
>> >
>> > jimcip at earthlink.net
>> > _______________________________________________
>> > Phono-L mailing list
>> > http://phono-l.oldcrank.org
>>
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