Pride Amp Series User manual

PRIDE DX-300
Service Manual
Amp Series
Copyright © 2004 CBTricks.com
Version. 1.0

Be sure to stop by the CBTricks web site and check it out.
http://www.cbtricks.com/
A WORD OF THANKS TO THE FOLLOWING PEOPLE FOR HELPING WITH THIS MANUAL.
Chris Reifsteck (Nomad Radio) , Joe Piatt, and N-Channel.
Safety Instructions
READ FIRST BEFORE
SERVICING THIS
AMPLIFIER
Lethally high voltages are present inside the amplifier unit. Never remove either top or bottom cover when power
line is connected. DO NOT attempt to operate unit when covers are removed:
1) Lethal voltages would be open to contact.
2) Protective interlock on top cover will short circuit the high voltage power supply; attempting to operate under
these conditions can cause damage to power supply, amplifier tube, or both.
3) Attempting to operate the unit with bottom cover removed causes loss of air pressure to the tube, and can cause
rapid failure of the tube.
4) Attempting to operate the unit with top cover removed (with the interlock blocked) may make the amplifier erratic
in tuning and performance due to the high level of R.F. on the top chassis coupling to the coaxial input cable at the
rear of the chassis. If repairs should be necessary, contact the factory, or a repair facility with proper equipment and
technical experience for the servicing of high power amplifiers.
If covers need be removed, allow two minutes after turning the unit off and unplugging the line cord before removing
covers.
Disclaimer: Although the greatest care has been taken while compiling these documents, we cannot guarantee that the
information is 100% correct with that said we do feel that this is the most accurate information out there. The publisher assumes
no liability for damages resulting from errors or omissions, or the violation of any law from use of this information. This also
covers unsuccessful attempts to repair the equipment covered in this manual.
The service and modification information shown here are provided for properly licensed operators only!
The user is solely responsible for making sure that any modifications made to the unit must meet all Federal and State
Regulations for the Country of use! Liability of damages to any equipment is the sole responsibility of the user!
Modifications are provided for information / educational purposes only!
Copyright © 2004 CBTricks.com / Bennie Bolin
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means,
electronic, mechanical, photocopying, or otherwise, without the prior written permission of the copyright holder (CBTricks.com).
All logos and Brand Names are the property of their respective owners.
http://www.cbtricks.com/

I
Pride DX-300 INDEX
PAGE
CHAPTER 1 Introduction
1.0 Introduction: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Specifications: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
CHAPTER 2 Operation
2.0 Installation: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . .
2
2.1
Operation: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.
3
CHAPTER 3 Circuit Description:
3.0 Introduction: . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
3.1 High Voltage Supply: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . .
5
3.2 Screen and Bias Supplies: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3 Low Voltage Supply: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4 R.F. Input and Control: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
3.5 Safety Interlock: . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.6 Wattmeter: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . .
9
CHAPTER 4 Maintenance
4.0 Plate Current Measurement: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1 Bias Voltage Adjustment: . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
4.2 Wattmeter Calibration: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.3 Input SWR Adjustment: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.4 Voltage Checks: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.5 Preventive Maintenance: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.6 Tube Replacement: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
CHAPTER 5 PCB Layouts
5.0 Low Voltage Supply PCB: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
5.1 High Voltage Supply PCB (Board #1): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
5.2
High Voltage Supply PCB (Board #2): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
5.3 Wattmeter PCB: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
5.4 RF Input and Control PCB: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
5.5 Safety Interlock PCB: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
5.6 PCB Trace Layouts: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
PCB Trace Layouts (Cont.): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.7 Chassis Layouts Front and Rear: . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
5.8
Chassis Layouts Top and Bottom: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
CHAPTER 6 Parts Lists
6.1 High Voltage Power Supply PCB #1: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
6.2 High Voltage Power Supply PCB #2: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.3 Safety Interlock PCB: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.4 Low Voltage Power Supply PCB: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.5 RF Input and Control PCB: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
6.6 Wattmeter PCB: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
6.7 Chassis: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
Chassis (cont.): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

II
Pride DX-300 INDEX
CHAPTER 7 Circuit Modifications
7.0 Introduction: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
7.1 Screen LED Modification: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
7.2 Screen Supply Modification: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
7.3 Tube Oscillation: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
7.4 Wattmeter PCB Modification: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.5 Bias Circuit Modification Version 1: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
7.6
Bias Circuit Modification Version 2: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
CHAPTER 8 Component Information
8.0 Introduction: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.1 Antenna Change Over and Preamp Relay Information: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
8.2 Band Switch: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
8.3 Input Coil Detail: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 33
8.4 Z1 Detail: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.5 Z2 Detail: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.6 Blower Detail: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.7 Part Suppliers: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Nomad Radio Replacement HV Power Supply Kit Information 35
CHAPTER 9 Schematics
9.0 Introduction: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Main Schematic: . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
Power Supplies: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
RF Section: . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
Inter-Connection Diagram: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
40

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Copyright © 2004 CBTricks.com
Pride DX-300 CHAPTER 1
1.0 INTRODUCTION:
In putting together this manual I started with the Pride DX300 factory manual added information that was missing
and in error, put together new updated schematics and PCB layouts.
The Pride DX-300 is a high frequency linear amplifier covering the Amateur bands from 3.5 to 30 MHz.
Pride Electronics in San Diego CA was a manufacturer of RF amplifiers and VFO's, as well as
frequency counters. The products that Pride built where assembled by handicap people hence the slogan printed
on the back of the amplifier “Manufactured with Pride by the Handicap”. I think that most of the DX300’s
where built between 1977 and 1978. Some people say that Pride was in the business of selling CB amplifiers
under the guise of amateur radio amps.
The Pride DX300 has no screen regulation, no feedback, and no screen or grid metering it was designed to
provide a medium power amplifier with high power gain at LOW COST.
It does have a receiver preamplifier, and automatic RF actuated switching. The amp has no mistuning protection
but with care anyone should have not problems with tuning it using the TUNE mode.
1.1 SPECIFICATIONS:
Power Ratings:
Mode Drive Power
SSB 15 watts peak. 1000 watts PEP input 650 watts nominal peak output any band.
CW 10-12 watts. 750 watts input, 50% duty cycle, 500 watts nominal output any band
AM 4-6 watts. 500 watts input, 5-minute cycle, 300 watts nominal output any band.
Frequency Coverage:
3.5 to 4.0 MHz
7.0 to 7.3 MHz
14.0 to 14.35 MHz
21.0 to 21.45 MHz
28.0 to 29.70 MHz
Device Complement:
1 4CX250B ceramic/metal tetrode
1 2N2905 receiver preamp transistor
1 2N2905 RF switching transistor
24 1N4007 rectifier diodes
5 1N4001 rectifier diodes
3 1N914 small signal diodes
Metering Functions:
Meter reads RF power output.
Amplifier tube screen current is monitored by an LED indicator.
Receive amplifier and power amplifier status are also monitored by LED indicators.
Front Panel Functions:
Power On/Off switch
Receive preamp on/off switch
SSB delay on/off switch
Tune/Standby/Operate switch
Plate tuning control
Band selector switch
Plate Loading control
Rear panel Functions:
Bias adjustment pot, Metering Jack and Input / Output RF connections.
AC Power Requirements:
120VAC 60 Hz, 500watts average 1000watts absolute peak.
Dimensions:
12" wide x 9" high x 12" deep.
Weight:
29lbs.

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Copyright © 2004 CBTricks.com
Pride DX-300 CHAPTER 2
2.0 INSTALLATION:
1) Select a location for your amplifier. RF amplifiers need ventilation, so choose a location that will not restrict the
air flow around the amp and where it won’t get water, coffee, or soft drinks spilled on or in it.
2) Connect a short length of coaxial cable from the exciter to the amplifier input connector. RG58/U or RG8/U
may be used and a PL 259 connector is required at the amplifier end of the cable. This cable should be as short
as is practical, preferable less than five feet.
3) Connect antenna or suitable high power dummy load to the output connector of the amplifier using RG8/U
coax. The smaller RG58/U coax may be used with matched antenna systems (better than 1.5 to 1 SWR) but will
have somewhat higher loss. The amplifier will match most loads from 25 to 100ohm.
4) Exciter power levels above 12 watts PEP or 5 watts carrier level should be avoided as over drive of the
amplifier will occur.
5) The unit should be grounded for R.F. by attaching a ground strap of coaxial shield or 10-12 gauge wire to the
ground post on the amplifier. This should be connected by a short run to a ground rod or cold water pipe. The
idea is to have a short direct earth ground to keep the chassis at radio frequency ground. In many cases normal
operation can be had without such a ground, but a good ground can help prevent television interference, and
make tuning straightforward.
6) The A.C. line cord should be plugged into a three-wire outlet. The electrical circuit should be capable of
handling a 10-ampere load.
Figure 2-0 Rear Panel

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Copyright © 2004 CBTricks.com
Pride DX-300 CHAPTER 2
Figure 2-1 Front Panel
2.1 OPERATION:
1) Check to see that the TUNE/STANDBY/OPERATE switch is in the center or STANDBY position. Apply power
to the unit by switching the POWER switch to the ON position. You will hear the cooling blower come up to
speed. Wait 60 seconds for the tube to come up to operating temperature.
2) During the time that the amplifier is warming up or at any time that the TUNE/STANDBY/OPERATE switch is
in the STANDBY position, the exciter may be operated normally "straight through" the amplifier.
3) Set the band switch to the same band as that the exciter is tuned to.
4) After warm up, place the TUNE/STANDBY/OPERATE switch into the TUNE position. The OPERATE
indicator will light up, indicating that the unit is ready for operation. If the RECEIVE switch is on, the RECEIVE
indicator will light also, indicating operation of the receive preamplifier.
5) Rotate the PLATE LOADING control to the nine o'clock (counter clockwise) position.
6) Apply several watts of drive from the exciter and quickly peak the PLATE TUNE control for maximum output
as indicated on the front panel wattmeter. The SCREEN overload indicator may glow at this time, and will peak
in brilliance at approximately the same place of tuning that maximum output occurs.
7) The PLATE LOADING control is then turned clockwise 1/2 division or so, and the PLATE TUNING control is
peaked again for maximum output. The brilliance of the SCREEN indicator will peak again, but not quite as
brightly as before. This process is continued until a further increase in the PLATE LOADING control will give no
further increase in power output. This will normally result in approximately 100watts output for three to four watts
of driving power.
8) Un-key the exciter, and place the TUNE/STANDBY/OPERATE switch in the OPERATE position. When the
exciter is keyed again, the power output will be somewhat higher, and the SCREEN indicator may glow brightly
again. Repeat the procedure as before, tuning the PLATE LOADING and PLATE TUNING controls alternately
for maximum output. The PLATE TUNING control should always be the last control that is adjusted. Power
output should be about 250watts for five watts drive at this point in the tune up procedure. When proper loading
is accomplished, the SCREEN indicator should glow only dimly. The plate current, as read on an external meter,
should be in the neighborhood of 200-250ma.

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Copyright © 2004 CBTricks.com
Pride DX-300 CHAPTER 2
9) For SSB operation, drive power should now be gradually increased to 10 or 12 watts, and the unit peaked for
maximum output. This can be done using the carrier insertion control on some exciters, or if this is not available,
a steady tone may be applied to the microphone input. When maximum power has been achieved, operation
consists of simply keying the microphone and speaking. The SSB delay switch should be in the on position,
which will give the R.F. actuated relays a time delay, so that they won't chatter during transmission. During the
SSB transmission, power output peaks will occur so rapidly that the output meter will not be able to follow the
signal. If a monitor scope is available, it can be seen that the peak power is considerably better than the 400
watts or so that was obtained during tune up. The SCREEN indicator will flicker with the transmission level, and
will reach full brilliance at high peak power levels. This is a faster indicator of peak drive conditions than is the
power output meter.
10) For CW operation, tune up as in step nine above. Power output will be nominal 250 watts for 5 watts of
driving power. The SSB delay switch may be left in the on position to prevent relay chatter during keying.
11) The 4CX-250B transmitting tube has been proven is commercial and military uses where long life and
reliability are major factors. Although it is designed to work a little harder in amateur service, it will still be
extremely reliable if a few common sense rules are applied.
a) Make sure that the tube always receives a good airflow. Remember that a lot of watts are being packed into
that rather small package, and that the only way to keep it cool is to get air through the tube fins. Do not block
the top of the cabinet, or stack other equipment on the amplifier. Make sure that the rear of the chassis (where
the blower gets its air) is open to cool room air. If the bottom cover of the unit has to be removed for service, see
that it is replaced properly prior to plugging in the unit (for safety also). The bottom chassis must be pressurized
in order to force air through the tube fins.
b) Wait 60 seconds before applying drive to the tube. Allowing the tube to properly warm up will help you get the
longest service from it.
c) After a long period on the air, let the amplifier run in the STANDBY mode for a minute or so before turning off
the power switch. This allows the blower to bring the tube down to a cooler temperature fairly rapidly.
d) Avoid excessive R. F. drive to the amplifier.
e) Use care in tuning most tube failures are the result of operator error, not equipment failure. These transmitting
tubes are used for thousands of hours in commercial service, and similar results should be yours with
reasonable precautions.

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Copyright © 2004 CBTricks.com
Pride DX300 CHAPTER 3
3.0 Circuit Description:
The DX-300 power amplifier uses a 4CX-250B Tetrode ceramic/metal construction, and utilizes forced air-
cooling. It is in a grounded cathode, driven grid configuration that provides very high power gain, high peak
power output, and excellent linearity and harmonic suppression. The use of tuned input circuits and broadband
matching transformers permits low drive operation combined with additional rejection of exciter harmonics. Class
AB operation of the tube permits high peak powers with low distortion products and harmonics. The amplifier has
a tune function that restricts the power gain of the amplifier for easy, safe tune-ups. The use of a single tube in
the design avoids the problem of matching tubes and it also simplifies repairs. RF actuated switching eliminates
the need for switching contacts on the exciter, which are not found on some of the lower powered rigs on the
market. An internal receiver preamp provides approximately 10db of gain on the higher frequencies.
Power supplies:
3.1 High Voltage Supply PCB:
The high voltage supply consists of the plate supply transformer located on the top of the chassis, and the two
rectifier filter boards below chassis directly under the plate transformer. A bridge rectifier circuit is used, which
allows good utilization of the transformer. Both circuit boards are the same, with the exception of the jumpers
(JP1 and JP2), which determine whether the filter capacitors are on the high side of the series filter string, or on
the low side. The low side board also contains two 6.8ohm, 2W metering resistors (R24, R25).
Each board contains one half of the bridge rectifier circuit, with appropriate jumpers between the boards. The
filter string consists of six 100µf electrolytic capacitors (C11, C12, C13, C22, C23, C24) in series, with voltage
equalizing resistors (R9, R10, R21, R22, R23) across each one. The time constant of the filter when no current is
being drawn is approximately 20 seconds, so that supply will be largely discharged 60 seconds after turn off
(ALWAYS CHECK). The high voltage developed by the supply is approximately 2200 VDC no load, and 1800
VDC at 500mA.
Figure 3-1 High Voltage Power Supply

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Pride DX300 CHAPTER 3
3.2 Screen and Bias Supplies PCB:
The screen and bias supply is also bridge rectified, but with a center tapped transformer and filter string that
allows a split output voltage. Approximately 700 VDC is developed across the two 40µf filter caps (C33, C34),
but due to the circuit configuration this shows up as +350 and -350 VDC. The +350 VDC is fed through a 30ohm
metering resistor (R36) to the screen current. The -350VDC is fed through two power resistors to provide source
current for an 82 volt Zener diode (D25) that provides a stable bias supply voltage.
This -82 volt supply is dropped in a voltage divider consisting of the back panel bias pot and two 3300ohm, 2W
resistors (R40, R41) to provide an adjustable, stable bias source for the tube control grid.
Figure 3-2 Screen and Bias Voltage Power Supply
3.3 Low Voltage Supply PCB:
This supply consists of a full wave voltage doubler, which is supplied from the 6.3volt filament winding on the
smaller transformer. 12 to 15 VDC is developed for use of the receive preamp, relays and indicators.
Figure 3-3 Low Voltage Power Supply