Cornell Custom 80 User manual

CORNELL AMPLIFICATION
OWNERS MANUAL
Custom 80
MUSICAL EQUIPMENT DESIGN & DEVELOPMENT
Unit 13 Rosshill Industrial Park,Southend-on-sea, Essex. SS2 5PZ
England
Telephone/Fax :[phone]

INDEX
1. INTRODUCTION
CONSTRUCTION & DESIGN
2. TECHNICAL DESIGN
Pre-amp and outputstage
4. CONTROLS
5. THE SPECIFICATIONS
6. BLOCK DIAGRAM
Please read all instructions before operating unit!
if you require any further information regarding the Custom 80 amplifier or
other CORNELL products , please do not hesitate in contacting us.
D.C. Developments
CORNELL EQUIPMENT DESIGN & DEVELOPMENT
Unit 13 Rosshill Industrial Park, Southend-on-sea, Essex. SS2 5PZ England
Telephone:[phone]

INTRODUCTION
Thank you for choosing a Cornell custom 80 amplifier.
Your amplifier employs valve technology. It is hand built to Ministry Of Defence
(MOD) standards. Only top quality components are used so that you enjoy years of
trouble free use.
Please take time to read this manual, to ensure that you get the best from
your custom 80 amplifier.
CONSTRUCTION & DESIGN
Virtually all modern amplifiers are built, using printed circuit boards, which
means conductor tracks that connect components together, often run very close
to one another. When this happens, a small capacitance is produced. The result
of which is a substantial loss in both high frequency response and harmonic
richness.
The Cornell custom 80, is designed to avoid this by having specific point to
point wiring.
Components in the custom 80 are mounted onto a specially designed panel,
and then connected, using heat resistant wire and finally sealed using a
conformal coating to prevent noise and reduction of component life, caused by
moisture penetration.
The chrome-plated steel chassis hold specially designed, interleaved,
transformers, wound on impregnated paper bobbins to minimize the gap
between iron core and windings. The design ensures a very close reproduction
of the full harmonic spectrum of your guitar’s pick-ups.

TECHNICAL DESIGN
The Pre-amplifier
The custom 80 is designed to be simple in use, and yet produce the wide range of sounds that
the musician of today expects from a professional amplifier.
The ‘BASS’ and ‘TREBLE’controls work over the entire frequency range of your guitar,
allowing for increased amounts of low and high frequency adjustment.
The Output Stage.
Part of the output transformer of the custom 80 is a small independent winding that picks up
the signal being produced in the final stage of the amplification process. As the winding is in
the output transformer itself, it will exactly reproduce, the speakers signal. This output is
used to feed the line output , reproducing the sound of your guitar as accurately as possible.
These output are ‘off-ground’ ensuring that no earth loop can be produced, when they are
connected to a mixer or power amp.
The custom 80 amplifier output stage is Class AB1, This means that the
grids of the output valves are controlled by a negative voltage. This is
known as the bias voltage.
The method used in biasing greatly affects the tone of the amplifier. Should the bias be set to
high - cross-over distortion occurs and is constantly present in the sound of the amplifier,
creating a ‘fuzzy’ tone. If set to low, then the valves might start to ‘glow red’. This will
considerably reduce their life and result in expensive replacement. It is recommended that a
Qualified engineer re-bias the output valves when changed.
Tube Replacement
Tube life varies depending upon playing style and application. Power tubes have a
much shorter life than pre-amp tubes which can last for years.
To maintain the optimum performance of your amplifier, the tubes should only be
replaced with the same type tubes as specified below.
Your Custom 80 amplifier has 7 valves three pre-amp valves 12AX7 or ECC83, and
four power valves 6L6.
Warning
When changing tubes, ALWAYS unplug the amplifier and remember that the
TUBES ARE HOT! wait for the tubes to cool or replace tubes when amplifier has not
been used for several hours.

THE CONTROLS
1. INPUT Hi & Lo.
High impedance input connections for instruments
Input Hi provides 6db more gain than the Lo input.
2. VOLUME.
Adjusts the overall volume of the amplifier.
3. BASS.
Adjusts the amount of low frequency boost.
4. TREBLE.
Adjusts the amount of high frequency boost.
5. MAINS.
When illuminated the valve heaters are on and there is power to the amplifier.
6. STANDBY.
Connects power to the valves for operation, use standby mode for breaks in usage,
7. OUTPUT.
OUTPUT LOW position operates the power of the amplifier to 1/4 of its output.
OUTPUT HIGH position returns the amplifier to its full output.
8. LINE OUTPUT
The 3 pin mail socket on the base of the chassis next to the output valves is a 600 ohm
line output for use with a Mixer or power amplifier.
Pin 2 anc 3 are live and pin 1 is chassis earth.
9 OUTPUT SWITCH
The switch at the base of the chassis next to the line output is a impedance switch, this
switch should be pointing inward for normal use 8 ohms internal speakers and should
be switched to point outward for use with an 8 ohms extension cabinet totaling 4 ohms.
10 Mains Fuse
The fuse holder contains the mains fuse to the amplifier and
protects the amplifier from electrical faults.
Replace a failed fuse only with the same type and rating.
Do not operate the mains switch without a 30 second delay between operations.
There is an internal thermistor to reduce mains surges.
The Thermistor works by introducing a resistance in the circuit when switched on.
Within a few seconds the thermistor is heated and the resistance is reduced.
It then takes a few seconds to cool and retain its initial resistance.

THE SPECIFICATIONS
POWER.............................................. 230 Volt AC 50hz 120 Watts
115 Volt AC 60hz 120 Watts
FUSE .................................................F2 Amp 240v Slo-blow for the 230v Model
F4 Amp 120v Slo-Blow for the 115v Model
INPUT IMPEDANCE.................. HI 2.2 Meg Ohm. LO 136k Ohm.
CONTROLS...................................... Volume, Bass, Treble .
............................................................... (Reverb optional extra).
LINE OUTPUT ...……………… Coil tapped trom output transformer.
............................................................... 600ohms at 0.25 Watt.
OUTPUT........................................... 80/20 Watt R.M.S
SPEAKER......................................... 2X Tone Tubby 16 ohm
............................................................... with 8 to 4 Impedance selector.
CABINET.......................................... Ply wood-shell and baffel. Leather handle.
SIZE.................................................... Height 20in 510mm 21in-535 with foot
Width 26in 660mm
Depth 10in 260mm
WEIGHT........................................... 74 Lbs 34 Kgs.
OPTIONAL ON REQUEST....... Speaker, Colours, Modifications.
WARNING:
To prevent damage, fire or shock hazard, do not expose this unit to
rain or moisture.
No user serviceable parts inside, refer servicing to qualified
personnel only.
This unit must be Earth grounded, use correct mains cord.

Custom 80 BLOCK DIAGRAM
INPUTS
TONE
CONTROLS
Hi
Lo
BASS TREBLE
Output
Switch
8
4
Line Output
VOLUME
2
1
3
Speaker Outputs
Output Transformer
Power Transformer connections Only to be altered by
Qualified personnel
HT
Bias
Heater
A
B
C
D
E
F
Fuse Thermister
1
2
240 Va/c Mains
Connect 1 to A Blue
Connect 2 to F Brown
Join C & D Black/Red
B & E no connection
115 Va/c Mains
Connect 1 to A&D Blue/Red
Connect 2 to C&F Black & Brown
B&E Yellow/Orange no connection
100Va/c Mains
Connect 1 to A&D Blue/Red
Connect 2 to B&E Yellow and
Orange
C&F Black/Brown no connection
BLUE
YELLOW
BLACK
RED
ORANGE
BROWN
BLUE
Mains
Switch