PF-20T and PF-50T
Bass Guitar Amplifiers
Owner’s Manual
IMPORTANT SAFETY INSTRUCTIONS
PF-20T / PF-50T Bass Guitar Amplifier
1. Read these instructions.
2. Keep these instructions.
3. Heed all warnings.
4. Follow all instructions.
5. Do not use this apparatus near water.
6. Clean only with a dry cloth.
7. Do not block any ventilation openings.
Install in accordance with the manufacturer’s
instructions.
8. Do not install near any heat sources such
as radiators, heat registers, stoves, or other
apparatus (including amplifiers) that produce
heat.
9. Do not defeat the safety purpose of the
polarized or grounding-type plug. A polarized
plug has two blades with one wider than the
other. A grounding-type plug has two blades
and a third grounding prong. The wide blade
or the third prong are provided for your safety. If the provided plug does not fit into your
outlet, consult an electrician for replacement
of the obsolete outlet.
10. Protect the power cord from being
walked on or pinched particularly at plugs,
convenience receptacles, and the point
where they exit from the apparatus.
11. Only use attachments/accessories
specified by the manufacturer.
12. Use only with a cart,
stand, tripod, bracket, or table
PORTABLE CART
WARNING
specified by the manufacturer,
or sold with the apparatus.
When a cart is used, use
caution when moving the
cart/apparatus combination
to avoid injury from tip-over.
13. Unplug this apparatus during lightning
storms or when unused for long periods
of time.
14. Refer all servicing to qualified service
personnel. Servicing is required when the
apparatus has been damaged in any way,
such as power-supply cord or plug is
damaged, liquid has been spilled or objects
have fallen into the apparatus, the apparatus
has been exposed to rain or moisture, does
not operate normally, or has been dropped.
15. This apparatus shall not be exposed to
dripping or splashing, and no object filled
with liquids, such as vases or beer glasses,
shall be placed on the apparatus.
16. Do not overload wall outlets and
extension cords as this can result in a risk
of fire or electric shock.
17. This apparatus has been designed with
Class-I construction and must be connected
to a mains socket outlet with a protective
earthing connection (the third grounding
prong).
18. The MAINS plug or an appliance
coupler is used as the disconnect device,
so the disconnect device shall remain readily
operable.
19. For the terminals marked with symbol
of “ ” may be of sufficient magnitude
to constitute a risk of electric shock. The
external wiring connected to the terminals
requires installation by an instructed person
or the used of ready-made leads or cords.
WARNING — To reduce the risk of fire or electric shock, do not
expose this apparatus to rain or moisture.
Laite on liitettävä suojakoskettimilla varustettuun pistorasiaan.
Apparatet må tilkoples jordet stikkontakt.
Apparaten skall anslutas till jordat uttag.
2
RISK OF ELECTRIC SHOCK! DO NOT OPEN!
CAUTION: TO REDUCE THE RISK OF ELECTRIC SHOCK DO NOT
REMOVE COVER (OR BACK). NO USER-SERVICEABLE PARTS INSIDE.
REFER SERVICING TO QUALIFIED PERSONNEL.
The lightning flash with arrowhead symbol within an equilateral
triangle means “electric shock hazard”. It is intended to alert
the user to the presence of uninsulated “dangerous” voltage
within the product enclosure, that may be of significant
magnitude to constitute a risk of electric shock to persons.
The exclamation point within an equilateral triangle means
“Warning/Caution!”. It is intended to alert the user of the
presence of important operating and maintaining (servicing)
instructions in the literature accompanying the appliance.
CAUTION
PF-20T / PF-50T Bass Guitar Amplifier
NOTE: This equipment has been tested
and found to comply with the limits for a
Class B digital device, pursuant to part 15
of the FCC Rules. These limits are designed
to provide reasonable protection against
harmful interference in a residential
installation. This equipment generates,
uses, and can radiate radio frequency
energy and, if not installed and used in
accordance with the instructions, may
cause harmful interference to radio
communications. However, there is no
guarantee that interference will not occur
in a particular installation. If this equipment
does cause harmful interference to radio or
television reception, which can be determined
by turning the equipment off and on,
the user is encouraged to try to correct
the interference by one or more of the
following measures:
• Reorient or relocate the receiving
antenna.
• Increase the separation between
the equipment and the receiver.
• Connect the equipment into an outlet
on a circuit different from that to which
the receiver is connected.
• Consult the dealer or an experienced
radio/TV technician for help.
CAUTION: Changes or modifications to this
device not expressly approved by LOUD
Technologies Inc. could void the user’s
authority to operate the equipment under
FCC rules.
This apparatus does not exceed the
Class A/Class B (whichever is applicable)
limits for radio noise emissions from digital
apparatus as
regulations of the Canadian Department
set out in the radio interference
of
Communications.
Exposure to extremely high noise levels may
cause permanent hearing loss. Individuals
vary considerably in susceptibility to
noise-induced hearing loss, but nearly
everyone will lose some hearing if exposed
to sufficiently intense noise for a period of
time. The U.S. Government’s Occupational
Safety and Health Administration (OSHA)
has specified the permissible noise level
exposures shown in the following chart.
According to OSHA, any exposure in excess
of these permissible limits could result
in some hearing loss. To ensure against
potentially dangerous exposure to high
sound pressure levels, it is recommended
that all persons exposed to equipment
capable of producing high sound pressure
levels use hearing protectors while the
equipment is in operation. Ear plugs or
protectors in the ear canals or over the
ears must be worn when operating the
equipment in order to prevent permanent
hearing loss if exposure is in excess of
the limits set forth here:
Duration, per
day in hours
8 90
6 92
4 95
3 97
2 100
1.5 102
1 105
0.5 110
0.25 or less 115
Sound
Level dBA, Slow
Response
Typical Example
Duo in small club
Subway Train
Very loud classical music
The boss screaming at his minions about manual deadlines
Loudest parts at a rock concert
Correct disposal of this product: This symbol indicates that this product should not be disposed of with your household waste,
according to the WEEE directive (2012/19/EU) and your national law. This product should be handed over to an authorized
collection site for recycling waste electrical and electronic equipment (EEE). Improper handling of this type of waste could have
a possible negative impact on the environment and human health due to potentially hazardous substances that are generally
associated with EEE. At the same time, your cooperation in the correct disposal of this product will contribute to the effective
usage of natural resources. For more information about where you can drop off your waste equipment for recycling, please
contact your local city office, waste authority, or your household waste disposal service.
3
TABLE OF CONTENTS
Important Safety Instructions .............................................. 2-3
Table Of Contents .................................................................4
Introduction ..........................................................................4
PortaFlex Series Features ......................................................5
PortaFlex Series Front Panel Features ....................................6
PortaFlex Series Rear Panel Features .................................. 7-8
Some Suggested Settings .....................................................9
Favorite Settings .................................................................10
Changing the Tubes ............................................................11
Setting Tube Bias ................................................................12
PF-20T Technical Specifications and Block Diagram ..............13
PF-50T Technical Specifications and Block Diagram ..............14
Service Information .............................................................15
Introduction
PF-20T / PF-50T Bass Guitar Amplifier
The Portaflex series bass amplifiers brought legendary Ampeg tone in powerful
lightweight design that bass players around the world, from beginners to professionals,
have made the most popular bass amplifiers in history. The PF-20T and PF-50T deliver
legendary Ampeg all-tube tone and warmth in the same portable, powerful and affordable
design.
Designed to be compact and match perfectly with existing Portaflex cabinets,
the PF-20T and PF-50T are perfect for small to medium sized shows, studio recording
or even a rehearsal studio. Combined with the PF-112HLF compact cabinet, you have
the ultimate portable tone powerhouse.
Like all Ampeg products, your Portaflex series bass amplifier is designed by musicians
and built using only the best of components. Each amp is tested to confirm that it meets
our specifications, and we believe that this amp is the absolute best that it can be.
In order to get the most out of your new amp, please read this manual before
you begin playing. Best of luck in all of your musical endeavors!
And thank you for choosing Ampeg.
4
PF-20T / PF-50T Bass Guitar Amplifier
PortaFlex PF-20T / PF-50T Features:
• RMS power output:
20W @ 4 or 8 ohms [PF-20T]
50W @ 4 or 8 ohms [PF-50T]
• Preamp: All-tube 2 x 12AX7
• Power amp:
All-tube 2 x 6V6 [PF-20T]
All-tube 1 x 12AU7, 2 x 6L6 [PF-50T]
• 0 dB and -15 dB inputs [PF-50T]
• Tone controls: Bass, Mid, Treble
• Mid-tone control: 5-position [PF-50T]
• Ultra Hi/Lo boosts [PF-50T]
• Input gain control
• Preamp balanced line out
• Pre/Post EQ
• Ground lift
• Transformer balanced line out
• Ground lift
• No speaker load required
• User-adjustable bias control
• Dimensions:
7.3 x 13.0 x 10.4 in / 185 x 330 x 264 mm [PF-20T]
7.3 x 13.9 x 10.4 in / 185 x 353 x 264 mm [PF-50T]
• Weight:
15.2 lb / 6.9 kg [PF-20T]
19.4 lb / 8.8 kg [PF-50T]
5
PF-20T / PF-50T Bass Guitar Amplifier
PortaFlex Series Front Panel Features
5
3 4
1. PF-20T INPUT: The signal output from
an instrument (active or passive) may
be connected to this 1/4" input by
means of a shielded instrument cable.
PF-50T INPUT: The signal output from
a passive instrument may be connected
to this 1/4" input by means of a shielded
instrument cable.
2. –15 dB INPUT: The signal output from
an active instrument may be connected
to this 1/4" input by means of a shielded
instrument cable. [PF-50T]
3. GAIN: This control adjusts the input level
of signal reaching the preamp.
4. ULTRA LO: This switch, when engaged,
emphasizes the lows by +2 dB at 50 Hz
and –10 dB at 500Hz. [PF-50T]
5. ULTRA HI: This switch, when engaged,
enhances the amount of high frequency
output by +5 dB @ 8 kHz. [PF-50T]
6. BASS: Use this to adjust the low
frequency level of the amplifier.
The low frequency output is flat
at the center position. See pages
13-14 for technical specifications.
86 7 9 101 2
7. MID: Use this to adjust the midrange
frequency level of the amplifier.
The midrange frequency output is flat
at the center position. Rotate the control
counter clockwise for a “contoured”
sound (more distant, less midrange
output) or clockwise for a sound which
really cuts through. See pages
13-14 for technical specifications.
8. FREQUENCY: This control allows you
to select the center frequency for the
midrange control, giving you a choice
of five “voices” for the midrange.
The numbers correspond to the
following center frequencies:
1=200 Hz, 2=400 Hz, 3=800 Hz,
4=1.6 kHz, 5=3 kHz. [PF-50T]
9. TREBLE: Use this to adjust the high
frequency level of the amplifier.
The high frequency output is flat
at the center position. See pages
13-14 for technical specifications.
10. VOLUME: Use this to control the
overall output level. It affects the
speaker outputs and the preamp
output. Use it wisely, and turn it down
when making connections or trying
something new.
6
PF-20T / PF-50T Bass Guitar Amplifier
PortaFlex Series Rear Panel Features
/
13 14 1511 12 1716 1918 20
11. POWER SWITCH: Use this switch to
turn the overall system power on or off.
Press the top of the switch to turn on
the power. The power switch should be
engaged prior to the standby switch (as
mentioned below, #12).
12. STANDBY SWITCH: Use this switch
to turn the standby power on or off.
Press the top of the switch to disengage
the standby circuit [ON position]. The
Standby mode allows the tubes to warm
or remain warm without high voltage
being applied to them. This extends tube
life. This switch should be OFF when first
turning the amplifier on. Allow the unit
to warm up for at least 20 seconds
before switching to the ON position.
During short periods of non-use, the
amp should be put into Standby mode.
13. FUSE: This protects the unit from
damage due to overload conditions
or power line surges. If the fuse blows,
replace it only with the same size and
type.
14. IEC POWER INPUT CONNECTOR:
This is where you connect the supplied
AC power cord. Plug the male end of
the cord into a grounded AC outlet.
DO NOT DEFEAT THE GROUND PRONG
OF THE AC PLUG!
15. BIAS SECTION: This control and set
16. POST-EQ/PRE-EQ: The signal at
17. PREAMP OUT: This signal may be used
The lift/gnd switch [18] is available
18. LIFT / GND: When this switch is
19. TRANSFORMER BAL OUT: This signal
The lift/gnd switch [18] is available
21
of LEDs allow the user to properly bias
the power amp. See “Setting Tube Bias”
on page 12 for a complete description
of how to use this section.
the preamp out can be set to either
Pre-EQ or Post-EQ with this switch.
With the switch in the IN position,
the signal at the preamp out is Pre-EQ.
This is a direct output not affected
by any EQ or boost settings. With
the switch in the OUT position, the
signal is Post-EQ and is controlled
and modified by the tone controls.
to feed an external power amplifier,
mixing console, interface or house PA
system.
to reduce any noise that may occur.
engaged, it connects the ground
connection to help reduce residual hum
and buzz sometimes picked up in the
signal cables.
may be used to feed an external power
amplifier, mixing console, interface or
house PA system.
to reduce any noise that may occur.
7
PF-20T / PF-50T Bass Guitar Amplifier
PortaFlex Series Rear Panel Features Continued...
21. SPEAKER OUTPUT: This mono 1/4" TS
21
20
20. IMPEDANCE SELECTOR: Use this
switch to match the output impedance
of the amp to the speaker(s) being
used (4 or 8 ohms).
For help in deciding the total impedance
of your system, consult the chart below.
Cabinet Number of Total
Impedance Cabinets Impedance
2 ohms 1 2 ohms
4 ohms 1 4 ohms
4 ohms 2 2 ohms
8 ohms 2 4 ohms
8 ohms 4 2 ohms
output jack supplies speaker-level power
to the speaker cabinet. The rated power
output is 20 watts rms [PF-20T] or 50
watts rms [PF-50T] into 4 or 8 ohms.
Make sure the total speaker impedance
load is 4 ohms or greater.
For example, you could connect:
2 16 ohm speakers in parallel = 8 ohms
2 8 ohm speakers in parallel = 4 ohms
Use speaker cables with 1/4" TS ends
to make the connections. Do not use
instrument cables as they may overheat.
NOTE: Unlike many tube heads which
require a load (speaker) be attached
for operation, the PF-50T / PF-20T
may be operated with or without
a speaker load attached.
This is extremely useful for direct
recording or bypassing a speaker
entirely in a live setting. This is also
useful should the speaker become
disconnected during performance,
as the amplifier will not be harmed.
8
Some Suggested Settings
JAZZ:
IN
FUNK:
IN
IN
PF-20T / PF-50T Bass Guitar Amplifier
The setting of the Gain
control depends on your
particular instrument.
The Volume should
be set to produce
the appropriate output.
ROCK:
FACE MELTER:
9
Favorite Settings
PF-20T / PF-50T Bass Guitar Amplifier
10
PF-20T / PF-50T Bass Guitar Amplifier
Changing the Tubes
Tubes wear out in direct proportion to how often and how hard you play your amplifier. Power tubes
should be checked at least once a year – more frequently if you use the amplifier nearly every day. When
power tubes wear out, the amplifier will begin to grow weak, lack punch, fade up and down, or lose highs
and lows. Power tubes work together in a push/pull configuration and should be replaced at the same
time with matched or balanced tubes. Your dealer can recommend the best replacement tubes for your
amplifier.
Preamp tubes aren’t worked as hard as power tubes and typically last longer. When a preamp tube wears
out, the amplifier may squeal, get noisy, lose gain and sensitivity, or just quit working. A service center
can determine which tube(s) may need replacing.
To get to the tubes in the PF-20T / PF-50T, the top screen must be removed first.
Qualified service persons may follow these steps to change the tubes:
• Turn the amp off, unplug it and let it cool for at least 5 minutes.
• Remove the screws which hold the perforated metal screen to the top of the chassis [Figure A].
• Set the perforated metal screen aside.
• Using a soft cloth, grasp the POWER tube as closely to the base as possible and gently work
it out of its socket by rocking it slightly back and forth as you lift up on it [Figure B].
NOTE: The retainers at the base may be spread apart to help remove the tube.
NOTE: The PF-50T has a 12AU7 Power Tube, but it is removed / attached similarly to the
Preamp Tubes (instructions below).
• Using a soft cloth, carefully replace the POWER tubes by handling them as closely to the base
as possible and firmly pressing down into the tube sockets.
Power Tubes
Preamp Tubes
Figure B [PF-20T]Figure A
• Grasp the PREAMP tube retainer at its top, push down and twist left [counter-clockwise] until the
tabs line up with the notches and lift up on it to remove [Figure B].
• Using a soft cloth, grasp the PREAMP tube as closely to the base as possible and gently work
it out of its socket by rocking it slightly back and forth as you lift up on it.
• Using a soft cloth, carefully replace the PREAMP tube by handling it as closely to the base
as possible. Line up the connector pins with the socket, then press down into the tube socket
to lock the tube into place.
• Replace the perforated metal screen and screws.
• Power up the amplifier and let it sit for at least 20 minutes. Bias the amplifier as directed
on the next page.
Figure B [PF-50T]
11
PF-20T / PF-50T Bass Guitar Amplifier
Setting Tube Bias
Turn the power on and allow the unit to sit in ‘Standby’ for 3-5 minutes (after following all normal setup
requirements). Next, take the unit out of ‘Standby’ and do a quick check of the Bias LEDs. One LED should
be lit green and the other LED off. If not, turn the Bias control until the LED is lit green. If this seems
impossible, please refer to the chart on the next page for possible fault conditions. Now is a good time
to check for any unusual sounds and possible glowing from the Power Tubes (see ‘Changing the Power
Tubes’ section listed above).
At this time, play your bass for at least 20 minutes to allow the unit to warm up at proper AC line voltage.
You may notice that the other Bias LED illuminates red while playing. This is normal.
Next, turn down all controls on your bass and set it aside, leaving all amp controls alone. With no input
signal present, adjust the Bias control so that only the green LED is illuminated.
So where does one set the Bias? If neither LED is lit, the amp is over-biased (counter-clockwise). This will
result in some distortion in the power amp and a generally thin sound. If the green and red LEDs are lit,
the amp is under-biased (clockwise) and too much current is flowing to the power tubes. This will result
in a big, full sound, but will also reduce the life of the power tubes. For the longest tube life, but poorer
tone, set the Bias to JUST AS the green LED illuminates. For shorter tube life, but better tone, set the
Bias to JUST BEFORE the red LED illuminates.
Once set, the controls should not have to be changed except as needed for tube replacement, or to
compensate for tube aging. Note that the AC line voltage may vary from place to place and the LEDs will
vary slightly. This is normal.
By observing the LEDs as the Bias control is slowly rotated clockwise, a number of tube problems may
be diagnosed by the user as seen in the table below.
NOTE: Depending upon the bias setting, the red bias LED may light or flicker when signal is applied
to the amp input; this is a normal condition.
Condition Problem Solution
Green comes on, then red No problem The longer the green LED is on before the red LED
Red comes on, then green Tubes not properly matched Set slightly before green comes on, obtain matched
Red comes on, no green One or more tubes are non-functioning Check to make sure tubes are all seated properly; if so,
None on Possibly no high voltage or bad Bias Have unit checked by a service technician.
Both on all the time Possible bad Bias Control or bad tubes Have unit checked by a service technician.
Control or bad tube(s)
comes on, the better matched the tubes are.
tubes when possible.
find and replace bad tube(s).
12
PF-20T / PF-50T Bass Guitar Amplifier
PF-20T
PF-20T TECHNICAL SPECIFICATIONS
Preamp All-tube 2 x 12AX7
Power Amp All-tube 2 x 6V6
Output Power Rating 20 watts @ 8 ohms, 10% THD
20 watts @ 4 ohms, 10% THD
Signal to Noise Ratio 60 dB (20 Hz–20 kHz, unweighted)
Maximum Gain Input: 54 dB
Tone Controls Bass: +8/–12 dB @ 50 Hz
Midrange: +5/–15 dB @ 550 Hz
Treble: +13/–20 dB @ 4 kHz
Power Requirements 120 VAC, 60 Hz, 50W
100 VAC, 50-60 Hz, 50W
220-240 VAC, 50-60 Hz, 50W
Size (H x W x D) 7.3 in x 13.0 in x 10.4 in
185 mm x 330 mm x 264 mm
Weight 15.2 lb / 6.9 kg (approximately)
0dB INPUT
BASS TREBLE
12AX7
GAIN
12AX7
MID
12AX7
6V6
6V6
MASTER
8 OHM
4 OHM
12AX7
PRE/POST
SPEAKER
OUTPUT 20W
TRANSFORMER
LINE OUT
GROUND LIFT
BALANCED
LINE OUT
GROUND LIFT
13
PF-20T / PF-50T Bass Guitar Amplifier
PF-50T
PF-50T TECHNICAL SPECIFICATIONS
Preamp All-tube 2 x 12AX7
Power Amp All-tube 1 x 12AU7, 2 x 6L6
Output Power Rating 50 watts @ 8 ohms, 10% THD
50 watts @ 4 ohms, 10% THD
Signal to Noise Ratio 60 dB (20 Hz–20 kHz, unweighted)
Maximum Gain Input: 66 dB
Tone Controls Bass: +10/–10 dB @ 60 Hz
Midrange: +5/–20 dB @ 200 Hz, 400 Hz, 800 Hz
+5/–15 dB @ 1.6 kHz, 3 kHz
Treble: +13/–23 dB @ 4 kHz
Ultra Lo: +2 dB @ 50 Hz, –10 dB @ 500 Hz
Ultra Hi: +5 dB @ 8 kHz
Power Requirements 120 VAC, 60 Hz, 90W
100 VAC, 50-60 Hz, 90W
220-240 VAC, 50-60 Hz, 90W
Size (H x W x D) 7.3 in x 13.9 in x 10.4 in
185 mm x 353 mm x 264 mm
Weight 19.4 lb / 8.8 kg (approximately)
-15dB INPUT
0dB INPUT
14
12AX7
12AX7
ULTRA
LO
GAIN
12AU7
BASS TREBLE
12AX7
ULTRA
HI
12AX7
6L6GC
6L6GC
MID
MASTER
MID
SELECT
8 OHM
4 OHM
12AU7
SPEAKER
OUTPUT 50W
PRE/POST
TRANSFORMER
LINE OUT
GROUND LIFT
BALANCED
LINE OUT
GROUND LIFT
PF-20T / PF-50T Bass Guitar Amplifier
Service Information
I
f you are having a problem with your PF-series amp, you can go to our website
(www.ampeg.com)
at 1-800-898-3211
assistance. If you are outside of the U.S., contact your local distributor for technical support
and service.
PF-series amps are covered with sheet metal, so be sure to clean it with a dry lint-free cloth. Never
spray cleaning agents on the PF-series amps. Avoid abrasive cleansers which would damage the finish.
Ampeg continually develops new products and improves upon existing ones. For this reason, the specifications
and information in this manual are subject to change without notice.
“Ampeg” is a registered trademark of LOUD Technologies Inc. All other brand names mentioned are trademarks
or registered trademarks of their respective holders and are hereby acknowledged.
and click on Support for service information, or call Technical Support
Monday-Friday during
normal business hours, Pacific Time
, to receive
www.ampeg.com
©2015 LOUD Technologies Inc.
16220 Wood-Red Road NE • Woodinville, WA 98072
Part No. SW1126 Rev. B 10/15
15
PF-20T and PF-50T
Bass Guitar Amplifiers
Owner’s Manual
Loading...