[Collins] Interpretation of 30L-1 manual, sec. 4.7

[Robert Jefferis]

Greetings all.

This afternoon I was reading 30L-1 manuals to clear memory cobwebs before adjusting a unit. I happen to have the 5th and 8th editions on hand. When I got to the "TUNE METER ADJUSTMENT", section 4.7.g., I noted what I feel is a confusion factor. Once you have increased exciter drive to the point of distortion onset, you should see a minimum of 450 V p-p on the scope (if you use this method). The 450 V p-p minimum output voltage requirement is clearly associated with the peaks of the 2-tone RF waveform envelope. This would correspond to a minimum output requirement of 506 Watts into 50 Ohms.

Since this check is done with 2-tone excitation, why would the RMS voltage, 160 VRMS (actually 159 if you run the numbers corresponding to 450 V p-p ) be stated in the manual ? Since my scope can only handle 400 V p-p without an external calibrated attenuator, I don't use the measurement method called for. Instead, I place directional couplers in the input and output lines of the amplifier to create an X-Y display on the scope. I can get much more reliable detection of distortion onset. I also place a wattmeter in the amp output line. My interpretation of all this is that the minimum power output with 2-tone excitation at distortion onset, as indicated by a wattmeter should be 506/2=206 Watts.

Have I missed something?

Yes, I know that the Tuning Indicator can be problematic, but IMO, it needs to be set up correctly, regardless of how you tune the amp when in service.

Bob, KF6BC