78 Recording Speeds.

[zooterman]

Hi All.
It is my understanding that different record companies did not all record at 78 rpm, if this is so how do I find out at what speed they did record, has anyone published a list.
Wal

[Coffee Phil]

You are correct that in the early days of recording (acoustic) speeds were all over the place. You are probably best to run your machine where the pitch sounds correct.

With the advent of electrical recording synchronous AC motors were used. The angular speed of 60 Hz is 3600 RPM and for 50 Hz is 3000 RPM. The speed of the lathe would be either of those numbers divided by an integer. In the United States the speed would be 3600 RPM / 46 = 78.2609 RPM. On your side of the pond I believe that they used 3000 RPM / 38 = 78.9474 RPM.

As an aside 33 1/3 can pe had precisely from 60 Hz or 50 Hz.

I have provided a link which as well as this subject talks about the multitude of EQs used untill the RIAA curve was agreed upon.

Phil

Hi All.
It is my understanding that different record companies did not all record at 78 rpm, if this is so how do I find out at what speed they did record, has anyone published a list.
Wal

[/url] http://www.videointerchange.com/vintage_78s.htm

[Terry Robinson]

It's not really possible to know, or find out what speeds recording companies used in the days of 78s. In the very early "accoustic" days, speeds ranging form 60 - 90+ r.p.m. were encountered however, even when electrical recording came along, speeds were "all over the place".

British Columbia, for example, used 80 r.p.m. until about 1930 and Victor used to make their "pop" records at about 76 r.p.m. so that they would "brighter" when played at 78 (I may be wrong about that exact 76 speed, but I do know they were designed to sound brighter).

The primitive cutting lathes used back then had no speed control and speeds often varied both within a side, and between sides. Unfortunately, transfer engineers often assume a 78 should be played at 78. And that's why we have both a varible speed gramophone, and a variable-speed C.D. player here.

Cheers,

Terry.

[Whitneyville]

Terry, you are "more" correct. Until at least 1935, German recording companies used 66 2/3 RPM as their "standard". I have classical recordings from that era, and they almost sound like a 33 1/3 RPM record being played at 45 RPM. Pathe stayed with 88.3 RPM until 1933, again, I have recordings of "The Trio of The Hot Club of France" t h a t s o u n d s o o o s l l o o o w w w and the timing marking on the labels aren't correct at 78.1 (US "Spec"). Spainish, Italian, Mexican, South American records in the electrical era were often cut at 90 RPM, which is why older record players (like my sister's) 1950 Zenith Cobra-Matic used a big variable rheostat on the drive motor so you could adjust for Edison (90 RPM) discs and all the other "odd speeds". There are dots marking the most common faster and slower speeds on now "my" Cobra-Matic. BTW: Most US early "Jass" records were cut at 70 or 72 RPM so they played back "faster" at 78 or on Victrolas. The timbre of the trumpet and clarinet (not to mention saxophones) give it away to this old horn-blower in a split-second.

[Coffee Phil]

I guess that I must have not read what I linked and other stuff with sufficient care. It appears that even after electrical recording started the recording companies had their own speed "standards" as well as EQ standards for some time.

Edisons were 80 RPM. Tom did not put it on the records but he did put it on some record jackets.

Phil

Terry, you are "more" correct. Until at least 1935, German recording companies used 66 2/3 RPM as their "standard". I have classical recordings from that era, and they almost sound like a 33 1/3 RPM record being played at 45 RPM. Pathe stayed with 88.3 RPM until 1933, again, I have recordings of "The Trio of The Hot Club of France" t h a t s o u n d s o o o s l l o o o w w w and the timing marking on the labels aren't correct at 78.1 (US "Spec"). Spainish, Italian, Mexican, South American records in the electrical era were often cut at 90 RPM, which is why older record players (like my sister's) 1950 Zenith Cobra-Matic used a big variable rheostat on the drive motor so you could adjust for Edison (90 RPM) discs and all the other "odd speeds". There are dots marking the most common faster and slower speeds on now "my" Cobra-Matic. BTW: Most US early "Jass" records were cut at 70 or 72 RPM so they played back "faster" at 78 or on Victrolas. The timbre of the trumpet and clarinet (not to mention saxophones) give it away to this old horn-blower in a split-second.

[/img][img][album]18446[/album]

[Whitneyville]

Phil, I certainly don't have "perfect pitch" anymore (if ever!), but listening to "78's" from different companies and countries (all electronic recordings) and listening to the timbre of the instruments, I know I can get with-in +/- 5% of the actual speed, usually better than that. I'm fairly confident some Eastern European records and some Soviet Records were cut perhaps as fast as 105 RPM. That's the only thing that makes the recording time even close to right, and the only thing that makes Jingo Rhinehardt sound "right" on some Romanian discs. NHK of Japan used 72 RPM until the end of WWII. The recording of His Imperial Majesty's Surrender Speech (one copy is in the Library of Congress) is recorded at 72 RPM. Telefunken record players on WWII German U-Boats have a setting for 66 2/3rds RPM. They are 36 volt DC motors BTW, and I have seen and heard a working one, right next to an "Enigma" code Machine, at the old Museum of Science and Industry in Chicago ca. 1984.

[Coffee Phil]

I just have relative pitch so the speed would have to be off a lot before I would notice it without a reference. I guess that is why I accepted that record speeds got standardized after electrical recording started.

The German 66 2/3 RPM is a sweet spot like 33 1/3 RPM in that it can be derived from both 50 and 60 Hz synchronious machines.

I am facinated with your Zenith record player. Is the speed control electrical? I am trying to imagine an affordable 1950s technology to do that. I have heard of Zenith machines of that vintage which used light, mirrors, and a photocell for the pickup. Is yours one of those?

Phil

Phil, I certainly don't have "perfect pitch" anymore (if ever!), but listening to "78's" from different companies and countries (all electronic recordings) and listening to the timbre of the instruments, I know I can get with-in +/- 5% of the actual speed, usually better than that. I'm fairly confident some Eastern European records and some Soviet Records were cut perhaps as fast as 105 RPM. That's the only thing that makes the recording time even close to right, and the only thing that makes Jingo Rhinehardt sound "right" on some Romanian discs. NHK of Japan used 72 RPM until the end of WWII. The recording of His Imperial Majesty's Surrender Speech (one copy is in the Library of Congress) is recorded at 72 RPM. Telefunken record players on WWII German U-Boats have a setting for 66 2/3rds RPM. They are 36 volt DC motors BTW, and I have seen and heard a working one, right next to an "Enigma" code Machine, at the old Museum of Science and Industry in Chicago ca. 1984.

[Whitneyville]

The Cobra-Matic uses an RF oscillator at about 485Khz modulated by a coil-type pick-up. This is then fed to the 455KHz IF of the radio section, then direct converted from 30Khz to audio frequencies as I understand the system. A 30Khz oscillator is very simple to build stable, and so is the 455KHz IF oscillator. I'm not 100% clear if the 30Khz signal is run thru the tiny coil in the cartridge and modulated that way or not. My "service manual" is just a "block diagram" type, and I haven't had the spare $100 +/- for a "real service manual". Zenith did do the photo-electric cell thing a few years later, as well as a "dynamic stress cartridge" which was a transistor with the stylus connected to the emitter I think. Zenith and Bell Labs had some smoozing going on until the early '60's. Zenith sold the first fully transistorized radio in the US, built around Motarola/Fairchild trannies. The fact that the radio/record player still works after 60 1/2+ years is a tribute to when we used to build things to LAST.

[Coffee Phil]

I did an internet search for this Zenith RF type phono pick-up and the best I was able to find was a mention of its existance. I would like to know how it works. Is there any chance you can scan the block diagram and post it. With that I may be able to figure it out.

Also the speed control especially if it is electrical has got to be interesting.

Thanks,

Phil

The Cobra-Matic uses an RF oscillator at about 485Khz modulated by a coil-type pick-up. This is then fed to the 455KHz IF of the radio section, then direct converted from 30Khz to audio frequencies as I understand the system. A 30Khz oscillator is very simple to build stable, and so is the 455KHz IF oscillator. I'm not 100% clear if the 30Khz signal is run thru the tiny coil in the cartridge and modulated that way or not. My "service manual" is just a "block diagram" type, and I haven't had the spare $100 +/- for a "real service manual". Zenith did do the photo-electric cell thing a few years later, as well as a "dynamic stress cartridge" which was a transistor with the stylus connected to the emitter I think. Zenith and Bell Labs had some smoozing going on until the early '60's. Zenith sold the first fully transistorized radio in the US, built around Motarola/Fairchild trannies. The fact that the radio/record player still works after 60 1/2+ years is a tribute to when we used to build things to LAST.

[Whitneyville]

I'll give it a shot Phil. The speed control is a big 1/3 arc of about a 15" diameter rheostat controlling the rim-drive motor. It's continuously variable, but as long as you come from the "Off/top speeds downwards" with the adjustment knob, it's surprisingly accurate. I'm going to have to break-down and buy a copy-of-a-copy of the real service manual, to get the adjustments on the record-player right and the "tweeks" after I've replaced the tubes right. The tube that's for the phonograph pick-up is still microphonic as heck, and I've replaced some of the old paper caps on the tube socket. I'm wondering about some of those oooold micas on there now.

[Coffee Phil]

That rheostat must be dealing with some serious power. I'm guessing that the motor is a brush motor although they may have been able to use a high resistance rotor induction motor.

Is the offending tube in the tone arm? What is the type number? If a quieter tube of the same type can't be found it may be possible to change the socket and use a nuvistor tube. They are very small and are constructed of ceramic and metal. As microphonics go they should be as good as you can get in a tube.

Mica capacators are very stable in value and have low loss. I understand that the leads on the old micas were attached with some sort of mechanical crimp which can fail. I don't ever remember replacing a failed mica capacitor but I seem to remember hearing that COG ceramic was developed in WW2 as a more reliable alternative to them. At any rate if they are working and you can tap on them with a pencil and they are not microphonic, I'd let them be.

Phil

I'll give it a shot Phil. The speed control is a big 1/3 arc of about a 15" diameter rheostat controlling the rim-drive motor. It's continuously variable, but as long as you come from the "Off/top speeds downwards" with the adjustment knob, it's surprisingly accurate. I'm going to have to break-down and buy a copy-of-a-copy of the real service manual, to get the adjustments on the record-player right and the "tweeks" after I've replaced the tubes right. The tube that's for the phonograph pick-up is still microphonic as heck, and I've replaced some of the old paper caps on the tube socket. I'm wondering about some of those oooold micas on there now.

[Whitneyville]

It's a shaded pole induction motor, awfully similar to a Dual turret drive motor. You could call it a "C" frame motor, but it has alot more torque at 16 2/3 RPM than you'd expect from the typical cheap "C" frame motor. The motor shaft is about .25" and the idler wheel is no more than 2.5", and the platter is about 10", so the motor turns fairly slow. My weird tube is a metal cased 12J5 which is an octal based tube separated from the rest of the chassis. I know this high-mu tube tends to be microphonic, but even the metal chassis shield several inches away from the tube, now makes the near "feedback" ring. I'm suspecting some bypass caps elsewhere are contributing to this. You know how hard it is to find anyone who knows how to work on these old five tube radios, with the Zenith RF phono circuit?

[Coffee Phil]

It's a shaded pole induction motor, awfully similar to a Dual turret drive motor. You could call it a "C" frame motor, but it has alot more torque at 16 2/3 RPM than you'd expect from the typical cheap "C" frame motor. The motor shaft is about .25" and the idler wheel is no more than 2.5", and the platter is about 10", so the motor turns fairly slow. My weird tube is a metal cased 12J5 which is an octal based tube separated from the rest of the chassis. I know this high-mu tube tends to be microphonic, but even the metal chassis shield several inches away from the tube, now makes the near "feedback" ring. I'm suspecting some bypass caps elsewhere are contributing to this. You know how hard it is to find anyone who knows how to work on these old five tube radios, with the Zenith RF phono circuit?

For the motor I am guessing that they used a very high resistance rotor. They are not great for effiency but they give good torque at high slip speeds. If you control the speed with a rheostat you are deliberately allowing high slip. The synchronus speed is 3600 RPM for a two pole and 1800 for a four pole. If you have a low resistance rotor as the speed drops below the synchronous speed the slip frequency increases so the rotor looks inductive and the resultant rotor current phase angle shifts reducing torque. If the rotor is kept resistive the torque will be more controled by stator current and less a function of speed.

The 12J5 is not all that weird. It is a 12 volt heater version of the 6J5. The 6J5 was at one time common as dirt. It is a medium mu (~20) triode used for amplifiers and local oscillators in AM radios. It is similar to 1/2 of a 6SN7.

Since it has a 12 volt heater tube and 5 tubes I'm guessing that it is similar to the "classic" AC/DC all American 5. I worked on many of those during my high school years so I may be of some use getting your radio / phono up to speed.

I'll bet I could draw a schemo of an all American 5 from memory and not make more than a couple of mistakes.

By the way if it is an AC/DC (no power transformer) radio be very careful working on it as they can give you a nasty shock.

Phil

[Whitneyville]

Phil, I'm on SBC Yahoo! and they want me to pay them to up-load photos and scans, but I think I can "work-around" this using my cousin's cable DSL service. I may take you up on your offer for help. My new 12J5 may be "iffy" or defective too. I know a couple of repair shops with the excellent B&W tube testers/analyzers, but I hate to take their time on free testing.