P&H Electronics LA-400B User Manual

P&H Electronics Model LA-400B Linear Amplifier
Manual Update by NA5RC Page 1 of 6
INTRODUCTION
This manual has been reproduced by James Lawrence, NA5RC, a LA-400B owner. There
are some notes on page 6 not associated with the manual. Where liberties are taken, they
are so noted.
GENERAL DESCRIPTION
The Model LA-400B Linear Amplifier is a grounded grid amplifier employing pentodes
connected as high mu triodes. This circuit design makes possible a compact, medium power
amplifier.
When used with a suitable exciter, this amplifier will deliver a high quality signal whether used
for single sideband, amplitude modulation, frequency modulation, or CW.
A variety of output impedances may be matched by the pi network output circuit; however, a
low impedance load is recommended. The low impedance input circuit is untuned. This
feature simplifies multiband operation. A well-filtered power supply incorporating full wave
mercury vapor rectifiers is employed. The cabinet housing this amplifier matches many
popular exciters. High quality components are used throughout.
SPECIFICATIONS
Power Rating 400 Watts P.E.P. Input
Drive Requirement 20 Watts for maximum output
Driver Impedance 52-72 Ω (The driver should employ link coupling or other
means for DC return.)
Frequency Range 75 thru 10 Meters
Output Impedance 50-75 Ω on all bands
Metering Circuit Indicates RF Voltage Input, Plate Current, and RF Amperes
Output
Tubes 2 ea Type 816 Rectifiers
4 ea Type 1625 (modified)
OPERATING INSTRUCTIONS
Preliminary
1. Connect the driver to the coax fitting at the rear of the unit marked RF Input using a
short length of coax.
WARNING: Do not apply plate power without a suitable driver connection.
2. Connect a 52-72 Ω antenna or load to the coax connector marked RF Output located
near the center of the rear deck.
3. Provision for blocking bias from exciter on Rear Deck if desired (See Figure 1).
4. Plug the line cord into any 105-125 volt 50/60 cycle A.C. source.
5. Apply filament voltage and wait at least 60 seconds before any attempt is made to
apply plate voltage.

P&H Electronics LA-400B Specifications

General

Frequency Range	20Hz - 20kHz
Frequency Response	20Hz - 20kHz ±0.5dB
THD	<0.1%
Output Power	400W @ 4 Ohms (200W per channel)
Damping Factor	>200
Dimensions	483mm x 88mm x 380mm (W x H x D)

Summary

Introduction

General Description

Specifications

Power Rating

Specifies the maximum power output capability of the amplifier.

Drive Requirement

Details the input power needed for maximum output.

Driver Impedance

Specifies the required impedance for the driving exciter.

Frequency Range

Defines the operational frequency bands of the amplifier.

Output Impedance

Specifies the impedance of the amplifier's output.

Metering Circuit

Describes the functions of the amplifier's built-in meters.

Tubes

Lists the types and quantities of vacuum tubes used.

Operating Instructions

Preliminary Setup

Initial setup and connection steps before powering on the amplifier.

Tuning Controls and Settings

Details on setting tuning, loading, coupling, and meter switches.

Inductance Settings by Band

Provides specific inductance settings for different frequency bands.

Tuning Procedure Steps

Step-by-step guide for resonating and optimizing amplifier output.

Chassis Rear View and Connections

Blocking Bias Connection

Instructions for connecting external bias or leaving it bypassed.

Meter Calibration Procedure

Steps to check and recalibrate RF voltage and current meters.

Parts List