v.2. Transmit Signal Levels
v.2.1. Transmit and VOX Audio Level Troubleshooting Guide
Source: Heathkit Service Bulletin HW-101-6
It is assumed that the basic steps such as making DC voltage measurement, checking
tubes & reviewing the soldering have been completed.
The following information was compiled from the above transceivers in the 80M LSB
position. The mike level control was at the 9:00 o'clock position.
AC signal voltages are listed below. These voltages were measured from the
microphone connector through the VOX circuit. All measurements were made with a
VTVM. A microphone or audio generator for 0.1V @ 1KHZ can be used as the signal
source.
Test Point Expected Level Measured Level
Mike Connector Lug 1 (set input level to) 0.1VAC
Pin 2 of V1 (note **) 0.02VAC
Pin 6 of V1 10-15VAC
Pin 5 Level Control (adjust mike level control for) 0.5VAC
Pin 9 of V1 (note **) 0.2VAC
Pin 8 of V1 (must be in VOX mode and not CW) 0.1 - 0.3VAC
Center Arm of VOX Sensitivity Control 5-15VAC
Pin 7 of V17 5-10VAC
Pin 6 of V17 40-50VAC
Junction of C211-D201 40-50VAC
Pin 9 of V12 (note this is VDC) 9-15VAC
note (*) value depends on setting of VOX sensitivity control
note (**) The expected values appear to be pulled down by loading of the voltmeter. I did not see this drop in my
measurements
Table 4. Transmit Audio & VOX Signal Levels
By tracing the AC signal from stage to stage the point of trouble can be isolated & steps
taken to correct it. The following are some possible trouble areas:
Check each of the shielded cables for a possible open or poorly grounded shield.
Check for continuity through each of the shielded cables.
Check for a proper ground at the mike control level.
If the frequency response of the audio stage is not within specifications check the values & installation of
C1, C2, C3 & C9.
Signal Level Measurements Page 49
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