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A New Design For The Drake L4B Amplifier

Written by: Ronald Baker / WB4HFN

>Contents<   Page 1   Page 2   Page 3   Page 4

Page 5   Page 6   Page 7   Page 8



In The Beginning

The Drake L4B Amplifier was designed and built in the middle 1960's as a two piece unit.   This included the (L4B) amplifier section and the (L4PS) high voltage power supply.   The amplifier was a very rugged amplifier and designed as a two final tube amplifier using the 3-500 or similar tube.  Over the last 40 plus years the amplifier section has survived well but the power supply is a different story.   The power supply by design produced over 2500 volts at almost 1 AMP.   Over time component failures in many cases has deemed the power supply as being non-repairable.    Typical problems include dried out filter capacitors, load resistors opening and high voltage arcing.   In most cases it is the lack of replacement parts or a bad transformer as reasons for being non-repairable.   Today you can find a surplus of the L4B amplifiers without the mating high voltage power supply.   The theme of this article presents one possibility in giving the old girl a new life.

    Shown in the pictures below is the original Drake L4-B amplifier and the mating L4PS high voltage power supply which Drake Manufacturing sold between 1965 to around 1979.     The earlier version of the L4B the front panel had the silver edging around the outside edge of the front panel all around, this matched with the Drake B-Line series.   The later version of the L4B the front panel was painted edge to edge to match with the newer Drake C-Line.


Table of Contents

Page 1

The L4B Amplifier Chassis Redesign

Page 2

High Voltage Transformer Installation

Page 3

The Input Circuit Redesign

Page 4

Chassis Reassembly

Page 5

The New High Voltage Circuit Board

Page 6

Amplifier Metering And Cooling Functions

Page 7

The New Low Voltage Power Supply

Page 8

The Completed Redesigned Drake L4B Amplifier


 Related Article Links

Drake L4/L4B Blower Fan Repair/Upgrade

High Speed Switching (QSK) For the Drake L4B Amplifier

L-4B Power Switch Refurbishing Project

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