AM Transmitters – Page 5 – Engineering Radio

The Continental D323C medium wave transmitter

I found a 1981 Continental Electronics equipment catalog at an old transmitter site. These finds are great if one is interested in history and looking at the way things used to be done. This particular transmitter is a 2,000 KW (2,000,000 watt) medium wave unit:

Continental Electronics D323C, Circa 1981

I believe most units like this were destined for use by government broadcasters in either the middle east or Western Europe. I know there were several 1,000 KW medium wave stations in West Germany at one time. The Continental transmitter is basically two 1,000 KW units (323C) combined. They used a modified version of Doherty modulation, that is called “Screen and Impedance,” which accurately describes how it works. More information from the Continental Catalog can be found here: Continental D323C. The tubes (or valves depending on where you are located) used in the D323C were 4CW25000A tetrodes as modulators and IPA the final was a pair of X2159, which is an impressive tube.

EIMAC X-2159 water cooled power tetrode — EIMAC X-2159 water-cooled power tetrode

The tube sat anode up. The filament, grid, and screen connections are underneath. Cooling water was pumped through the two connections on the top at about 130 gallons per minute depending on the plate dissipation. With a 30° C rise, that equals about 96,000 BTU per minute. The D323C had a dissipation of 400,000 watts for the carrier tube and 240,000 watts for the peak tube (640 KW total) under 100% modulation. That equals about 2 million BTU per hour. Notice the lifting hook, this tube weight in at 175 pounds. Tube date sheet here.

Continental no longer makes medium wave transmitters, their closest high powered broadcast product now is the 418/419 and 420 HF (shortwave) transmitters. The 420D does a wimpy 500 KW using a solid-state modulator section.

I remember in the early 1990’s when I was at the Harris plant in Quincy, they were working on a 1,000 KW solid state DX series AM transmitter for Saudi Arabia. It had to be liquid cooled, which added another layer of complexity to an already complex system.

I don’t know if there is much call for 2 MW medium wave transmitters anymore as there are more efficient ways to reach remote populations and I can’t even imagine what the electric bill would be like.

The Gates BC1H

In my never-ending fascination with broadcast transmitters, I bring you the Harris/Gates BC1H. This is an updated model of the BC1G, the main difference being the solid-state audio and oscillator sections in the later H model. This design uses the simple 833 parallel final and 833 push-pull modulator

Sales brochure, click to download the four-page .pdf

Schematic:

Harris/Gates BC1H Transmitter running at 1,000 watts into the antenna. Like many old tube transmitters, this sounds great on the air. The transmitter was made in 1975 and is in backup service. For a 37 year old transmitter, it runs like a champ and comes on consistently. Like the preceding Gates BC-1 models, this transmitter is rugged and reliable. My only comment is the transistors in the solid-state driver section are no longer available. If that were to become an issue, one can always look up the tube audio driver from previous versions (T and H models). It would be a shame to throw away a good transmitter for lack of a couple of transistors, but I know some who have done just that.

Australian Made Broadcast Equipment

Somebody working to preserve a record of past work:

Some of these have familiar looking cabinets and tube arrangements. They all look like classics to me and it is good that they are being saved. I noticed at the end of the video there is a Harris MW10A. As for the RCA Ampliphase transmitters; I maintained a BTA5J in Harrisburg PA on 580 KHz. It was reliable enough, but I could never keep it sounding good for more than a couple of days.

In any case, a worthwhile effort. More information at: AWA Transmitters.

Harris exits the broadcast industry

When they sold their Broadcast Equipment supply division to SCMS a few years ago, the handwriting was on the wall. Even so, it is a little surprising that they would exit broadcasting altogether.

The decision to divest in no way reflects the quality of the work Broadcast Communications performed in support of our customers and our company. Harris simply determined that Broadcast Communications could provide higher value and operate more effectively under a different ownership model.

They are spinning the broadcast division off to a new owner rather than completely shutting down the operation. In an e-mail received from Harris Morris, President of, Broadcast Communications Division, clients and customers will still receive support for existing products:

In the interim, Broadcast Communications will continue to be a part of Harris Corporation and operate business as usual. Our valued relationships, both longstanding and new, remain our top priority. The global Broadcast Communications team will continue to work diligently to ensure our commitment to our customers and partners remains steadfast, our execution to fulfill commitments is flawless, and our progress against strategic objectives remains focused.

Well, there you have it. This affects such things as Harris transmitters (AM, FM, TV, HF) and support, Harris consoles and studio furniture (previously Pacific Recorders and Engineering or Pacific Research and Engineering, AKA PR&E), and Intraplex STL systems, among others.

What does all this say about the future of terrestrial broadcasting?

We live in interesting times.