info wanted test equipment

[Crenshaw, Jack]

I don't know about those particular items specifically, but I've recently
bought several vintage old tube-type versions of the same units.  They're
pretty slick.  Both units, however, require inputs from external sine-wave
oscillators to function.  The sine wave oscillator must itself have a clean
output.

The harmonic distortion meter is basically a tunable, active notch filter.
The unit that I have uses a Wien-bridge filter, with negative feedback to
sharpen up the notch.  Following the filter is what amounts to a wideband,
AC voltmeter.

What you do is to hook up a sine-wave oscillator, pass that through the amp
under test, and from there, drive the inputs of the meter.  Set the
oscillator to whatever frequency you want to test at, and use the
"calibration" switch setting (I've probably got that name wrong) to set the
meter sensitivity.  Then you tune the bridge to get a minimum reading on the
meter, changing scales as necessary.  The lowest reading is the residual
harmonics.  If you want to see what those residuals look like (i.e., 2nd,
3rd, etc) there's an output to a scope.

The Audio Analyzer is really three separate instruments:  A(nother) AC
voltmeter, a wattmeter, and an IM distortion meter.  This one requires _TWO_
clean sine-wave sources. The circuitry basically consists of two filters,
one high-pass, one low.  The frequencies are fixed.  The IM meter is
designed to work according to some standardized test procedure, which is to
combine two signals, I _BELIEVE_ 100Hz and 7000Hz, with specific ratios of
amplitudes.  The mixing should produce sum-and-difference frequencies of
6900 Hz and 7100 Hz. Anything else is distortion, usually caused by the LF
signal modulating the power supply, and therefore the gain of the HF one.
This produces extra combination frequencies that get past the filters.

The wattmeter is simply a resistive load you can hook up, which provides 4,
8, and 16 Ohm resistors.  The resistors are capable of measuring 50 watts
continuous, 75 watt in bursts.

Hope this helps.

Jack





> ----------
> From:         Paul Settle[SMTP:paulsettle at SOFTCOM.NET]
> Reply To:     paulsettle at softcom.net
> Sent:         Tuesday, August 29, 2000 4:35 AM
> To:   HEATH at LISTSERV.TEMPE.GOV
> Subject:      info wanted test equipment
>
>     Greetings
>         Just picked up two pieces of Heath test equipment and would like
> to get some information about them.
>         IM-48 Audio analyzer
>         IM-58 Harmonic distortion meter
>         Any info would be appreciated. Thank you.
>
> Paul
>
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