Cornell Rambler 15 User manual

Rambler 15 & 40
Owner’s Manual
DC Developments
Musical Equipment Design & Development
Unit 13 Rosshill Industrial Park, Southend-on-Sea, Essex SS2 5PZ England
Tel/Fax [phone]
www.dc-developments.com

© 1995-2007 CORNELL Musical Equipment Design & Development 2
CONTENTS
Introduction 3
Construction and Design 3
Technical Design 4
The Pre-amplifier
The Output Stage
Controls 5
Specifications 6
Valve Replacement 7
Please read all instructions before operating the amp!
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 earthed. Use the correct mains cord.
If you require any further information regarding the Rambler amplifier, or any other
CORNELL products, please do not hesitate in contacting us (details on front page).

Introduction
Thank you for choosing a Cornell Rambler 15 / Rambler 40 amplifier.
Your amplifier employs valve technology, and is hand built to the highest standards.
Only top quality components are used in our amplifiers, so that you can enjoy years
of trouble-free use.
Please take time to read this manual, to ensure that you get the best from your
Rambler 15 / Rambler 40 amplifier.
Construction and Design
Virtually all modern amplifiers are built using printed circuit boards, which helps to
speed up production and keep down costs. There is, however, one major drawback
with printed circuits - conductor tracks that connect components together often run
very close to one another, creating a small capacitance. The result of this in a
guitar amplifier is a substantial loss in both high frequency response and harmonic
richness.
Cornell amplifiers are designed to avoid this by having point-to-point wiring
throughout. Components are mounted onto a specially designed component board
which is then sealed, using a conformal coating to prevent noise and the reduction
of component life caused by moisture penetration.
The hand wiring, carried out by our highly-trained staff, takes time but ensures that
each of our amplifiers performs to the highest standards of reliability and sound.
The stainless steel chassis holds our specially-designed transformers, and chassis-
mounted (rather than circuit-board mounted) valves (tubes).
Such attention to detail ensures a very close reproduction of the full harmonic
spectrum of your guitar’s pick-ups, resulting in a pure, natural sound that will turn
heads at any venue and/or that records superbly.

© 1995-2007 CORNELL Musical Equipment Design & Development 4
Technical Design
The Pre-amplifier
The Cornell Rambler is designed to be simple in use and yet produce the wide
range of sounds that the musician expects from a professional amplifier, with the
superb tones that you can only get with valves.
Channel 1: The Bass and Treble controls work over the entire frequency range of
your guitar, allowing increased amounts of low and high frequency adjustment.
Channel 2: Has a core tone set to the mid-frequency range of the guitar. Gain and
Volume controls adjust the amount of overdrive; the Tone controls adjust the upper
and lower frequency range of the overdrive setting.
Reverb: Adjusts the amount of reverb signal. The reverb design on the Cornell
Rambler is such that it is independent of the dry signal. The two signals are mixed
together at the output stage, thus the reverb control is also the reverb volume. This
enables you to blend the amount of reverb you require; 100% can be achieved by
simply reducing the dry signal, i.e. the Master Volume.
The Output Stage
The Cornell Rambler 15 has a Class A output design achieved by means of fixed
bias resistors. The resistance values are selected to complement exactly the
characteristics of the output valve. Cathode bias resistors help to stabilise current
flow throughout the lifetime of the valve. The voltage across each bias resistor will
vary with the valve’s characteristics. When these voltages are equal, each valve is
drawing the same amount of current and the valve set is “matched” resulting in
maximum output and long life.
Our Class A design has less cross-over distortion, resulting in a smoother output
sound when the output stage is driven beyond its output level.
Cornell ‘Cream Box’
Part of the Cornell Rambler 15 sound is due to our little ‘cream box’. We can’t tell
you what’s inside - it’s our little secret. We think it makes our Rambler 15 sound
rather special. But take a listen and judge for yourself.
The Cornell Rambler 40 uses a Class AB output design. This configuration allows
greater output to be achieved without increasing the temperature of the output
valves unduly.
The sound of the Rambler 40 ranges from crystal clean to singing lead tones.

Controls
1. Input - Hi & Lo
Both inputs offer high impedance connections for instruments.
The Hi input 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. Gain - Adjusts the gain/overdrive of channel 2.
6. Reverb - Adjusts the amount of reverb (works on both channels)
7. Master - Adjusts the overall volume of the amplifier.
8. Mains Indicator
When illuminated, this shows that the valve heaters are on, and that there is
power to the amplifier.
9. Standby
Connects power to the valves for operation, use Standby mode for breaks in
usage (eg, between performance sets).
10. Valve/Diode Switch - Selects the rectifier type.
11. Output Switch
The three-position output switch selects full power (position ‘A’), 1/5 power
(position ‘B’), and 1/15 power (position ‘C’) [these figures are approximate]
12. Impedance Switch
The switch at the rear of the chassis next to the external speaker jack is an
impedance switch. This switch should be pointing downward for normal use
(with 8 Ohms internal speakers only, or 8 Ohms external speakers with the
internal speakers disconnected); and should be switched to point upwards for
use when an 8 Ohms extension cabinet is used in parallel with the internal
speakers (or some other combination totalling 4 Ohms). Using the correct
impedance selection enables the amp to deliver maximum power to the
speakers.
13. Mains Fuse
The fuse holder, next to the mains switch on the back panel, contains the
mains fuse for the amplifier. The mains fuse 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. This
protects the amp and helps to ensure a long life for the components. The
thermistor works by introducing a resistance in the circuit when the power is
switched on. Within a few seconds the thermistor heats up and its resistance
reduces, allowing the full current to flow into the mains transformer. After
switching off the amp, it takes a few seconds for the thermistor to cool down
and to return to its initial, protective resistance value.

© 1995-2007 CORNELL Musical Equipment Design & Development 6
Specifications
POWER Rambler 15 ....................... 230 Volt AC, 50Hz, 120 Watts
Rambler 40 ....................... 230 Volt AC, 50Hz, 280 Watts
FUSES Rambler 15 ........................ 500mA, 240v Slo-blow
250mA Slo-blow HT Fuse
Rambler 40 ........................ 1Amp, 240v Slo-blow
500mA Slo-blow HT Fuse
INPUT IMPEDANCE ....................... Hi - 2.2 MegOhm: Lo - 47 kOhm
CONTROLS ..................................... Volume, Bass, Treble [Channel 1]
Gain, Volume, Bass, Treble [Channel 2]
Reverb, Master
OUTPUT Rambler 15 ..................... 15/3/1 Watts
Rambler 40 ..................... 40/8/2 Watts
SPEAKERS .................................... 1 x 12” (Celestion/Jensen/Tone Tubby)
2 x 10” (Celestion/Jensen)
with 8 / 4 Ohms impedance selector switch
CABINET ......................................... Pine shell & plywood baffle.
Leather handle. Rubber feet.
SIZE ............................................... Height: 19in (490mm)
Width: 24in (600mm);
Depth: 9in (230mm)
WEIGHT .......................................... 51 lbs / 23 Kg
OPTIONS (on request) .................. Choice of speakers, covering material and
colours, grille cloth material/colours

Valve Replacement
Valve life varies, depending upon playing style and application. Power valves have
a much shorter life than pre-amp valves, which can last for years. In order to
maintain the optimum performance of your amplifier, the valves should only be
replaced with the same types of valve, as specified below.
Your Cornell Rambler amplifier has eight valves: three pre-amp valves (12AX7/
ECC83), two 12AT7/ECC81 valves for the reverb, two power valves (EL84for the
Rambler 15, and EL34 or 6L6 for the Rambler 40), and a rectifier valve (GZ34).
Warning
When changing valves, ALWAYS unplug the amplifier, and remember that the
VALVES ARE HOT! Wait for the valves to cool, or replace the valves when the
amplifier has not been used for several hours.
Valve Line-up
Mains
Transformer Output
Transformer
EL84 EL84 ECC83
Front panel
GZ 34 ECC81ECC81 ECC83 ECC83
6L6 or
EL34
6L6 or
EL34
Rambler 15
Rambler 40