[Table of Contents]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [ARSCLIST] Odd Speed

Well, there is another partial explanation.

Use a machine set for 3.75 in/s at 50Hz and use it on 60Hz, you'll make a recording at about 4.5 in/s made with 3.75 in/s EQ.

I saw one of these on paper tape in the Provincial Archives of Saskatchewan. I didn't realize it at that time, but it seems like the most logical explanation.  Fortunately, that tape had low-harmonic 60Hz hum on it, so I line-locked my oscilloscope and tuned the speed for a stable 60Hz. I got 4.4 in/s as the "proper" speed with that method, and that's within 2.2% of theoretical which is pretty good, all things considered.

I did a quickie table

If you used a 60Hz machine on 50Hz mains, then the tape recorded at the following speeds will play back at the second speed in the pair:

Nominal   Actual
  1.88        1.57
  3.75        3.13
  7.50        6.25
15           12.50
30           25.00

This requires a machine that can shift downward by 16.7%

Repeating the same exercise, but with a 50Hz record machine run on 60Hz mains, you get
Nominal   Actual
  1.88       2.26
  3.75       4.50
  7.5         9.00
15          18.00
30          36.00

This requires a machine that can shift upwards by 20%

Now, none of these sequences explains the 5 in/s in Don Chichester's email and 5.63 in Marie's original post, although this does explain the 4.4/4.5 in/s of the Saskatchewan tapes.

Also another point to ponder. I believe some early portable tape recorders used spring-wound motors and mechanical governors for the speed control.

This is distinct from the horrid "rim drive" machines from the 1960s -- which make all 3-inch reels suspect. No capstan at all, just a motor on the takeup reel and a rheostat in series between the battery and the motor.



At 04:33 PM 3/4/2004 -0500, you wrote:
About 15 years ago a friend sent me his reel tape collection of interviews he had made while doing a religious news show on the BBC.  He asked only that I might convert one or two tapes to cassettes for him.  Upon playing the tapeS! I found they were, in fact, recorded at about 5 ips!
I did the best I could at the time by increasing the size of the capstan until it came close to c. 5 ips.  
Evidently some recorders (for radio use???) recorded at 5 ips, or nearly so.  Else, why were there several such tapes?
Don Chichester

[Subject index] [Index for current month] [Table of Contents]