The Homebrew AM Transmitter Project

Transmitter OverviewThe Homebrew AM Transmitter project is unlike anything I have ever attempted to do. It basically consist of a modulator running a pair of 813s in class "AB2" with a RF deck using a single 4-400A running class "C" high level plate modulation. The exciter is 1940's era Millen 90800 using a 6L6 and a 807. The muscle behind the transmitter comes from a set of iron in the plate supply from Merit Transformer Corp. The transmitter will occupy an entire 63 inch high rack cabinet.

The overall design is based on a homebrew transmitter that was first built by Andy Howard (WA4KCY) using a pair of 4-125s modulated by a pair of 4-125s. A later design, using all 813s, was done by Dr Ron Johnson (WB4GWA). The drawing to the right is my attempt to show (using computer drawings), my version of how the transmitter will look once completed.

The progress of the transmitter will be documented on this web site as I complete the various sections. I will attempt to post as many photos as possible showing the details of the construction of the transmitter. This is also a way to keep pressure on myself to keep moving forward on the construction of the various sections. Check back to this web site from time to time and I will post the most resent photos first along with a posting date.

June 13, 2001

Merit A-P-7199This is the heart of the transmitter which is the plate transformer. It is made by Merit Transformer Corporation, model number A-P-7199. It has a 115 VAC primary with a 5600 VCT secondary at 750 mA. I'm not 100% sure but my guess is that this transformer weighs around 200 lbs, and is right at a cubic foot in size. The metal beams under it are the start of the metal frame that I built around the transformer in order to carry the transformer better.

This is view of the plate supply from the rear of the transmitter. The only component missing in this photo of the plate supply is the bleeder resistor network assembly, which has yet to be mounted. At the bottom is the plate transformer and the plexyglass assembly which holds the two solid state rectifiers. In the upper right is the 10 henry plate supply reactor made by Merit also. In the upper left is the 8 uF plate capacitor. Plate Supply

Semtech SA 7477This is a close up view of the two SemTech SA 7477 solid state rectifiers. Notice that they are mounted on a plexyglass assembly to avoid shorting out the plate supply to anything. The rectifiers came from an old VLF military transmitter.

This is a front view of the transmitter (with panels removed) showing the plate supply along with the control circuit relay assembly mounted on the front for easy access. Front View

Control RelaysThis is a close up view of the control circuit assembly. All the wiring is 14 awg wire except for the plate circuit which uses 10 awg wire. The large relay on the left is the plate relay.

This is the RF deck for the transmitter which uses a single 4-400A in the final. Another nice feature is the B & W 850A in the tank circuit. This RF deck was part of a homebrew amp that I got in an estate sale. The same homebrew amp used the same Merit plate supply. The RF deck, for the most part, is complete and ready to use. I will, however, replace the front panel and install new meters. RF Deck

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This page last updated 13 June 2001