W6BN.COM -- Collins Radio KWM-2 and S-Line Repair Service, T-Tubes, 30L-1 Boards

Bill Noonan, W6BN

Collins S-Line and KWM-2
Repair Service T-Tubes 30L-1 Boards

30L-1 Diode/Capacitor Board

This is the latest in a series of after market diode/capacitor boards designed for the popular Collins 30L-1 amplifier. Designed by a professional power supply engineer this one-piece diode/cap board replaces the two piece assembly provided as original equipment some forty plus years ago.

The components include a high temperature 130-degree C FR4 fiberglass circuit board. The 85-degree C capacitors are mounted on the opposite side of the board from the bleeder resistors, which are surrounded by ventilating holes to insure maximum cooling. The rectifier diodes are 1N5408 3-amp units. The high voltage multiplier resistor consists of four separate resistors rated at three watts each.

The original Collins cap board had a total of 16mf of filtering, the new combination board increases this figure to 25mf for improved dynamic voltage regulation.

We have conducted a number of side by side comparisons and tests and present the results for your inspection (preliminary, subject to change).

TEST                         ORIGINAL BOARDS              NEW BOARD            
                                                                               
Input Voltage To Amp.        120 VAC                      120 VAC              
                                                                               
Resting high voltage         1980 Volts DC                1980 Volts DC        
                                                                               
Voltage at 300ma load        1820 Volts DC                1820 Volts DC        
                                                                               
Ripple at no load            6 Volts P.to P.              2 Volts P. to P.     
                                                                               
Ripple at 150 ma load        84 Volts peak to peak        50 Volts peak to peak
                                                                               
Diode string rating          4.8 KV                       6 KV                 
                                                                               
Diode string current rating  600ma                        3 amps