PRS Guitars HDRX 50 User manual

Service Notes
Service should only be made by a qualified technician.
Tubes
Tubes are consumables, as they have a given usable lifespan. They are part of the heart of
the tone, so keeping correctly operating tubes is essential. Tubes can fail catastrophically
or gradually, and it’s good to know what to look for if they start to go bad. Periodically
inspect them and look to see if anything inside the tube is glowing cherry red other than
the normal orange glow of the filament. This would indicate a situation where the tube
is conducting more current than it is capable of handling and most likely about to fail.
Two other conditions to observe are: 1) filaments not glowing or 2) a miniature fireworks
display inside the tube. Any of the above conditions indicate serious problems with the
tube and should be taken care of immediately. Tubes quite oen are the cause of spurious
noise in the amp. Microphonic tubes will squeal or rattle with the vibrations induced by the
speaker cabinet. If suspected, tap each tube lightly with a pencil with the amp powered
up—the suspect tube will many times let you know. Note that there is a normal metallic
clinking when doing this, but a microphonic tube will be obviously louder.
Replacing preamp tubes will not require any adjustment, but the power tubes will need
rebiasing to assure proper operation. Aer power tube replacement, initially inspect the
tubes oen to assure there are no “cherry red” components within the tube. Tubes today
can have a wide variety of tolerances and a re-bias is highly recommended with new ones.
Power tube bias should be adjusted from a preferred setting with the HDRX amps of 29 mV
max., +/- 5 mV. If power tubes are mismatched by less than 5 mV, average the two around
29 mV. Mis-matched tubes beyond 5 mV can induce noise and may cause a degradation of
tone. It is always recommended to purchase and install “matched” power tube sets.
NOTE! Never power up the amplifier without power tubes installed, as voltages can
rise to levels that may damage internal components.
NOTE! Capacitors may retain an electric charge and can be dangerous even when the
unit is o, unplugged, and has not been played for an extended period of time. USE
CAUTION!!!!
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Product Number: 100497:::004 Rev. B
HDRX  AND 
USER’S MANUAL

Using your PRS Amplifier
IMPORTANT: Before using your amplifier, refer to the IMPORTANT SAFETY INSTRUCTIONS
insert supplied with the product.
Powering Up:
1. Make sure your speaker cabinet is connected to the correct speaker output impedance jack
with a high quality speaker cable. Do not use guitar cords.
2. Make sure the power cord is connected to the correct earthed (grounded) outlet.
3. Make sure there is at least 6 inches (150mm) of clearance around the amplifier to allow for
proper cooling. Never place the amplifier against a wall or other equipment, and keep it clear
of other heat sources, such as other amplifiers or stoves. Make sure there are no flammable
items, such as curtains, behind the amp. Do not drape items over the amps that can prevent
proper cooling. Do not set drinks or other liquids on top of the amp that can spill into the amp.
4. The amplifier is designed to be able to power up without the use of a Standby Switch. Just
turn the Power Switch to the On position and let the amplifier naturally warm up. Pull the
guitar cable out one click to mute the amplifier when necessary.
5. Turn the volume controls down to mute the amp, plug in the guitar cable or output of eects,
bring the volumes up slowly to the desired loudness and play some tunes. This amplifier can
produce very loud volumes so take care with this procedure to avoid volume surprises.
This equipment is capable of very high sound pressure levels. Prolonged exposure
may cause hearing damage.
This equipment contains no user-serviceable parts. Refer all repairs to qualified service
personnel.
This equipment is heavy and there is a risk of back injury. Li using correct safe liing
techniques.
Ensure that the mains plug is easily accessible to allow the unit to be powered o by
unplugging the power cable.
Only connect this unit to an earthed (grounded) supply socket.
THIS UNIT IS CLASS 1 CONSTRUCTION AND MUST BE EARTHED!
HDRX 50 and 100 Amplifier Front Panel Controls
Input: ¼” Standard Mono Guitar Cable. The input feeds two internally “jumpered” channels.
Bass Volume: Controls the “Bass”-voiced channel loudness and gain. Overall low frequency
tightness or looseness can be adjusted using this control.
Bright Switch: Three positions allow for subtle or bolder bright settings aecting the Treble
channel.
Treble Volume: Adjusts the higher-frequency “Treble”-voiced channel loudness and gain,
historically associated with “Lead” circuits. Balance the Treble and Bass Volume controls to set
the overall brightness or darkness and associated gain of the amp.
Treble Control: Tone stack control adjusting the high frequencies of the amp, aecting both
channels.
Gain Switch: Activates circuitry to boost the gain of upper-mid and above frequencies to add
clarity and cut when on, and smoothness when o. This switch aects both channels.
Middle Control: Tone stack control adjusting the midrange frequencies of the amp, aecting
both channels. This adjustment allows the user to add cut-through-the-mix fullness or body to
the sound, or create a “scooped”, crisp tone.
Bass Control: Tone stack control adjusting the low frequencies aecting both channels. Lower
settings will sound tighter, especially with more gain and higher settings will add deep fullness
and thump.
Presence Control: Adjusts power amp brightness by manipulating negative feedback aecting
both channels globally.
Power On/O Switch: The HDRX 50 and 100 amps were designed to not need Standby Switches
as part of properly powering the amp on. If necessary, a simple way to mute the signal is to pull
the input cable plug out one click.
Rear Panel Controls
Mains Socket: Always use the mains lead supplied. Your sales outlet can provide a lead suitable
for your country. Always disconnect the equipment from the mains and ancillary units before
moving the amplifier.
Fuses: This amplifier is equipped with multiple accessible and inaccessible fuses. Replacement
fuses must be of the same type and rating as indicated. Failure to comply may result in
permanent damage to the product, and/or create a safety hazard. Always disconnect the
equipment from the mains supply before replacing a fuse.
Mains Fuses: These are located in the mains socket. There is one active and one spare in the
socket tray. Fuse types and specifications required for your country/region are silkscreened and
marked below the Mains Socket.
B+ Fuse: The B+/H.T. fuse holder is accessible from the rear panel next to the Mains Socket.
B+/H.T. fuses should only be evaluated and replaced by a qualified technician.
Filament Fuses: These are located internally on the circuit board and should only be evaluated
and replace by a qualified technician.
Bias Jacks and Pot: These jacks measure the power tube current draw in milliVolts. There
will be one jack associated with one power tube. When metering, 1 measured mV = 1 mA of
current flowing through the associated power tube. The center jack in the bias array is ground,
and receives the Common probe on your meter. Review the information on the back of this
manual for guidance on replacing tubes. Biasing and tube replacement should be performed
only by a qualified technician. Bias adjustments can be made with a jewelers (small, 00 size
recommended) Phillips head screwdriver. The bias adjustment aects all of the tubes at the
same time. The bias jacks can allow you to determine if any tubes are dead and not functioning
(zero bias), or if they have dried up or down out of specification from the other tubes. In these
instances, individual tubes may be replaced with the same test rating numbers as the original
tubes and conveniently verified using the bias jacks and a meter when installed.
Speaker Jacks: These are the main outputs for your speaker cabinet(s). There are 5 total jacks
to use and include two 4 ohm jacks wired in parallel, two 8 ohm jacks wired in parallel, and
a single 16 ohm jack. Determine beforehand what your total speaker loading will be and use
the appropriate jacks. Never “mix” impedance jacks such as using the 16 ohm jack with the 8
Ohm jack at the same time. It is also not suggested to use two speaker cabinets with dierent
impedances as these combine to create odd impedance values and performance. For two 16
ohm cabinets in parallel (creating an 8 ohm load), plug each cabinet into one of the two parallel
8 ohm jacks. Similarly, for two 8 ohm cabinets in parallel (creating a 4 ohm load), plug each
cabinet into one of the two parallel 4 ohm jacks. Failure to correctly match the speaker load to
the appropriate output jacks can cause tube socket arcs, blown power tubes, or failure of the
amp.
High Voltage Warning! Do not touch bare loudspeaker connectors due to an electric
shock hazard. Power o when handling connectors.
Safety Symbols: The following symbols mean:
Warning: read instructions to understand possible hazard
Danger: electrical shock hazard
Warning: This equipment is capable of very high sound pressure levels. Prolonged
exposure may cause hearing damage.