http://www.engineeringradio.us/blog/2009/08/my-friend-the-mw-50b/ When I was 10, I caught the radio bug, it appears to be terminal Mon, 06 Feb 2012 20:11:15 +0000 hourly 1 http://wordpress.org/?v=3.3.1 http://www.engineeringradio.us/blog/2009/08/my-friend-the-mw-50b/comment-page-1/#comment-192 J. Aegerter Sat, 12 Dec 2009 19:33:35 +0000 http://www.engineeringradio.us/blog/?p=3928#comment-192 The PDM Class D power amplifier is very efficient, but with the very high voltages involved with this circuitry, flashover is a major problem. I think many of these problems were corrected in the MW50C, but at these voltages, cleanliness and weekly inspections are paramount. The GE BT-25 had better (larger) high-voltage insulators, the layout was not as compact, and the transmitter (with tubes) was designed to take large faults, whereas, the MW50 was more of a paper design than a field proven design. The original MW50 design used a Federal F-1099 vacuum tube damper diode. I actually think this may have been more reliable with the voltages involved. But, pressure to get "solid state" and trash those old antique energy wasting vacuum tubes, made the MW50B more sell-able. The PDM Class D power amplifier is very efficient, but with the very high voltages involved with this circuitry, flashover is a major problem. I think many of these problems were corrected in the MW50C, but at these voltages, cleanliness and weekly inspections are paramount. The GE BT-25 had better (larger) high-voltage insulators, the layout was not as compact, and the transmitter (with tubes) was designed to take large faults, whereas, the MW50 was more of a paper design than a field proven design. The original MW50 design used a Federal F-1099 vacuum tube damper diode. I actually think this may have been more reliable with the voltages involved. But, pressure to get “solid state” and trash those old antique energy wasting vacuum tubes, made the MW50B more sell-able.

]]> http://www.engineeringradio.us/blog/2009/08/my-friend-the-mw-50b/comment-page-1/#comment-27 Dave Thu, 20 Aug 2009 01:37:26 +0000 http://www.engineeringradio.us/blog/?p=3928#comment-27 please don't forget the little signal diodes located behind the power output meter panel. You can buy 10 of them for $1.49 at Radio Shack (I think 1N914), but god forbid one of them shorts following a lightning storm. They were meant to rectify the carrier and provide NEGATIVE feedback to the audio driver to stabilize the system and reduce distortion. Care to guess what happens when one of them shorts? Signal feedback to the audio stage, and it's not a pretty sight. Suffice to say when the transmitter is turned on the lights would dim in the rest of the building, but not in the transmitter room! It would be very bright in there. please don’t forget the little signal diodes located behind the power output meter panel. You can buy 10 of them for $1.49 at Radio Shack (I think 1N914), but god forbid one of them shorts following a lightning storm. They were meant to rectify the carrier and provide NEGATIVE feedback to the audio driver to stabilize the system and reduce distortion.
Care to guess what happens when one of them shorts? Signal feedback to the audio stage, and it’s not a pretty sight. Suffice to say when the transmitter is turned on the lights would dim in the rest of the building, but not in the transmitter room! It would be very bright in there.

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