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Radio Broadcast Technical Consulting and Sales
10032 Island Drive, Brainerd, MN  56401


Technical Tips from Mark W. Persons
Modified McMartin BA-1K


The McMartin BA-1K, 1000 Watt AM Radio Broadcast Transmitter, is factory wired to operate at two power levels.  Many daytime broadcasters received authority to run at night often requiring transmitters to be modified for three power levels. 

The photo shows three power control relays that select the primary (240 VAC) power input to the high voltage power transformer.  This is modified from the original two-relay configuration.  The three new 30-ampere relays fit comfortably on an aluminum plate above the transformer.

Another modification to the transmitter is a variable AC transformer, which has been mounted inside the transmitter cabinet with the control knob on the front near the bottom of the transmitter.  This adjusts tube filament voltage.  New 4-400 tubes can be set as low as 4.4 volts when the normal filament voltage is 5.0 volts.  This will dramatically extend the life of the tubes.


The power control relays are operated by relays added to the front inside panel of the transmitter. 

There are two pushbuttons to set which low power level the transmitter will run at. 

In addition, one of the yellow colored relays selects one of the two blue colored 10-turn pots to set the modulation level for each of the two low power levels. 

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 
Mark W. Persons   Ham WMH

Questions?  Email Mark Persons:  teki@mwpersons.com         

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page last edited 02/22/2016