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Title: Johnson Valiant correct PA bias voltage Post by: G4OJY on March 05, 2024, 06:01:51 AM So I've just finished restoring a Johnson Valiant transmitter but I've seen 2 figures quoted for the PA bias voltage of -52V and -69V. Which is the correct one to use? I'm only interested in transmitting on AM.
Andy G4OJY Title: Re: Johnson Valiant correct PA bias voltage Post by: ae7db on March 05, 2024, 01:29:08 PM Assuming you have an original Valiant, with bias adjustments being made with the sliders on the resistor, the attached clip from the manual calls for grid voltages of -70V for the rf finals and -55V for the modulators.
Dean Title: Re: Johnson Valiant correct PA bias voltage Post by: G4OJY on March 05, 2024, 01:36:17 PM Assuming you have an original Valiant, with bias adjustments being made with the sliders on the resistor, the attached clip from the manual calls for grid voltages of -70V for the rf finals and -55V for the modulators. Dean Hello Dean, its a MK1 Valiant which has had the mods to change it to the MK2, so there are 2 bias potentiometers on the side. Title: Re: Johnson Valiant correct PA bias voltage Post by: ae7db on March 05, 2024, 04:21:32 PM Andy, AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
OK. The manual for the Valiant II, as shown in the attached clip, calls for setting the rf final grid bias to -69V. It calls for adjusting the bias pot for the modulator finals to achieve a static current of 60mA rather than specifying a bias voltage. Dean |