[R-390] Sources for meter movements?

[Roy Morgan]

At 06:33 PM 6/8/2005, mikea wrote:
>You may find that the "Ideal VU Meter" isn't ideal for use as an S-meter or
>what-have-you in an R-390 or R-390A[1], because the damping on a VU meter
>is specified rather carefully and isn't the damping you'll see on most
>anything else.

Mike and others,

The characteristics of a "correct" VU meter are tightly specified in an 
official specification.  Basically:

1) the meter must indicate within one percent of "100 or 0 VU" within 0.3 
seconds of application of the signal
2) The overshoot must be more than 1% and less than 1.5 %.
3) The impedance of the meter may also be specified but I am not sure.

Ah yes, I have an RDH4 at hand (Radiotron Designer's Handbook Volume 
4).  In Chapter 19, Section 2, page 823, I find:

  " The Volume Indicator is a root-mean-square type instrument with a 
copper oxide type of rectifier.  The rectifier law is intermediate between 
linear and square-law, having an exponential of 1.2 +/- 0.2.  It's dynamic 
characteristics are such that if a sinusoidal voltage of frequency between 
35 and 10,000 c/s and of such amplitude as to give reference deflection 
under steady state conditions is suddenly applied, the pointer will reach 
99% of reference deflection in 0.3 seconds (+/- 10%) and then should over 
swing reference deflection by 1% but not more than 1.5%.  ... It will give 
a reading of 80% on an impulse of sine wave form as short as 0.025 second. .. "

The reference given for most of this is:
"American recommended practice for volume measurements of electrical speech 
and program waves" C16.5 - 1942 American Standards Association

I think it's unlikely that a small meter such as in the R-390 type 
receivers could meet these specs. The 0 VU calibration would, but none of 
the rest.  I have a genuine Weston VU meter about 4" across. It is VERY 
heavy. I suspect that the large magnet is needed to meet the ballistic 
specs above.

at:
http://yarchive.net/phone/decibels.html
I find the author (Al Varney)varney at ihgp2.ih.lucent.com
  tells his sources for VU meter information:
"   much of my VU information was from the Bell System Technical Journal, 
Vol 19, 1940, p. 94-137, "A New Standard Volume Indicator and Reference 
Level", by D. K. Gannett (Bell Labs), H. A. Chinn (CBS) and R. M. Morris 
(NBC).  This was also presented at a joint AIEE/IRE meeting in San 
Francisco (June 1939)
and at the IRE Convention in New York (September 1939).  Additional
material was from the June 1940 Bell Labs Record and several prior
documents relating to the Bell System's "program transmission networks"
and work of loudspeaker/public-address systems."

  At:
http://www.sfu.ca/sonic-studio/handbook/Zero_Level_VU.html
I find:

"0 VU is +4 dbm and represents a voltage level of 1.228 volts."

Note that 0 DBM in 600 ohms is one milliwatt or 0.733 volts, and no doubt 
these definitions can be found in many EE texts or engineering handbooks.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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