johnanthony888 wrote:So, when should I use a strobe disc? There is the danger like the turntable, after servicing the motor, to have a wrong speed (for example 85 rpm instead of 78 rpm?
The strobe discs can be used any time you want to check the speed of the turntable, but of course, this is normally done after the motor has been serviced, because it will run more smoothly.
The only "danger" would be if the turntable spun so fast that the rotating governor balls started hitting the housing, but if the motor's been properly rebuilt, that shouldn't be an issue. Since most "78s" were recorded at 78 rpm--rotations per minute, that would be the correct speed for them. If the turntable runs at 85 rpm, then the singers might sound like cartoon chipmunks. If it's much slower than 78 rpm, then they may sound like lumbering goons.
Now, not to complicate matters, but I should point out that standard disc records made BEFORE the 1925-1930 period, when turntable speeds were standardized, were NOT always recorded at 78 rpm. In some cases the speed was as high as 90 rpm, or as low as about 70 rpm. Finding out the correct speed can be a real challenge, but there are comprehensive discographies available, mostly from the used book market, and some are very expensive. There are also some online guides, such as --
http://www.normanfield.com/pitch.htm -- which is helpful if you have a sensitive ear for pitch. Some companies, such as Victor, told customers that 78 rpm was the recommended speed, even though they seldom recorded exactly at that speed prior to 1925.
I'd guess that most of the 78s you're likely to come across probably date from after the early 1930s, so this shouldn't be too much of an issue for you. I'm not very nitpickey about the "correct" speed, so I normally keep my Victrola turntables set right at 78 rpm. I've made it a habit to double check the speed, using a strobe disc, about once every month or two.
JDS
