Re: [ARSCLIST] Odd Speed

["Richard L. Hess" <ArcLists@xxxxxxxxxxxxxxx>]

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.

Cheers,

Richard


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