This transmitter is in service at WSBS, Great Barrington, MA as a standby. It was new in January 1975.
This was running into the dummy load for testing, which we try to do periodically.
The audio section is a pair of 8008’s 810s running in parallel. This goes through a modulation transformer to the RF section.
The RF section consists of another pair of 8008’s 810’s running parallel. The plate voltage for these tubes is 1,250 VDC which is fairly tame, all things considered. The transmitter is dirt simple 250-watt carrier power, 125% positive peak capable. It is not the most efficient unit under the sun but it can still be repaired with off-the-shelf parts.
This is a somewhat faded schematic. The schematic shows a single 833A as the final, however, this particular transmitter has a pair of 810’s for the final, as shown in the above picture. Ham radio operators love these things as they are easy to convert to 160 or 80 meters for AM phone use. The bigger brother to this unit is the Gates BC1G, which is also a pretty simple unit using 833A tubes in parallel with 3,500 VDC plate voltage.