[/url] http://www.videointerchange.com/vintage_78s.htmzooterman wrote: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.
[/img][img][album]18446[/album]Whitneyville wrote: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.
Whitneyville wrote: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 wrote: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 wrote: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 wrote: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?