Odd SP-600 modification

Don Stepka dts4 at CORNELL.EDU
Thu Oct 30 02:19:08 EST 1997

Going through my SP-600, I found a modification I'm curious about.  Does
anyone know if it's been published, and what the modifier thought it was

Symptom: RF meter did not indicate upscale -- strong signals read -6 dB.
Audio gain was lower than I'd like (particularly trying to rx SSB signals
without an SSB adapter).  Audio distortion was high.  The noise limiter
turned everything into heavily clipped mush.

Diagnosis: The detector was not to print.  My print shows the detector
cathode (V 14 pin 3) grounded.  The radio had the cathode grounded through
a parallel RC network: 130 pF and 470 K ohms.  This lowered the audio level
and the signal strength meter drive, causing difficulty receiving SSB and
CW signals.

Fix: Return radio to stock -- ground detector cathode.  Audio gain is good,
distortion is lower, meter works, and the limiter is its normal, merely
useless self instead of a guitar effects pedal.

There are other, more straightforward ways to lower the audio gain.  So
what was someone trying to accomplish with this modification?



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