Lyrita Audio GM70 SET User manual

Lyrita Audio
L - 458, Sarita Vihar
New Delhi 110 076
Tel : [phone]
email:viren.bak[email protected]
www.lyrita-audio.in
GM70 SET
Mono power amplifiers
Manual
Lyrita Audio

Guarantee
This amplifier is guaranteed against any defect in material
and workmanship for a period of two years from the date
of purchase. Tubes are guaranteed for thirty days.
Within this period, Lyrita Audio will repair the amplifier
without charge, provided that failure was not due to
misuse.
A separate guarantee card is not issued with this unit. The
guarantee period begins on the day you take delivery.
Model No. ________________
Specifications
Driver Tube Russian 6E5P (1 nos)
Output Tube Russian GM70 (1 nos)
Rectifier Tube Russian 6C5S (1 nos)
Power Output 35 watts per channel into 8 ohms
Sensitivity 3 V input for full output
Frequency Response 40 Hz to 20 kHz
Distortion (THD) less than 1%
Input Line level
Output Speakers
Mains Power 230 V, 50 Hz, 350 W (max)
Size W x D x H 360 x 520 x 200 mm
Weight 20 kg

Fuses
! Warning : In operation, this amplifier has high voltag-
es. Always switch off, and unplug the amplifier from the
mains supply before working on it. Wait for 5 minutes
for the high voltages to die down, before opening the
amplifier!
The amplifier is protected against overload by fuses at three
points. The mains supply fuse is mounted on the rear panel
and is easily accessed from the outside.
Inside the amplifier are two fuses on the high voltage sup-
ply. These are mounted on the inside panel above the pow-
er supply capacitors. To reach the internal fuses, remove
the back top plate of the amplifier.
Mains supply fuse 2 A, 250V (RQB 4000)
High Voltage supply fuse 200mA, 250V (RQB 200)
100mA, 250V (RQB 100)
On operation of the amplifier, if the fuses do blow, check all
possible causes before replacing the fuses. If any doubt
remains, contact Lyrita Audio for servicing.
Description
The GM70 SET Mono power amplifiers are single channel,
medium power, tube amplifiers, offering superb reproduction
of sound.
These amplifiers have to be operated using a preamplifier,
which controls all signals coming to the amplifiers. Lyrita
recommends using their DHT Line preamplifier.
The design is a single-ended triode tube amplifier, using the
GM70 DHT power tube, running in pure Class A mode. There
are two stages - the driver stage coupled through an
interstage transformer to the output stage. The output stage
uses a custom designed audio output transformer. No global
feedback is used. All wiring is point-to-point.
Fixed bias is used for the output tubes. No user adjustment is
required.
The power supply has an oversized transformer, to provide
good regulation for the supply voltages. Solid state
rectification is used for the output stage, and tube rectification
for the driver stage. Each stage of the high voltage supply is
independently filtered through chokes and special, high
voltage, film capacitors. Individual filament transformers are
used for low noise operation. A DC filament supply is used for
the output tubes.
The GM70 SET is housed in a naturally finished solid
sheesham cabinet. The design elegantly showcases the
beauty of the tubes.

Connections
Power
Mains supply connection is through a detachable power
cable with an IEC-type connector. The mains power
switch is mounted on the front panel of the amplifier.
Signal
The input signal connection is made to the RCA socket on
the back panel of the amplifier.
Speakers
The speaker output sockets accept banana jacks. The
norm here is Red for signal and Black for ground. Maintain
the colour code when connecting to the loudspeaker, so
that the speakers operate in phase.
Installation
The amplifier should be placed as close to the
loudspeakers as possible. This will allow the connections
to be made with short speaker cables. It is advisable to
keep the additional impedance seen by the amplifier as
low as possible. The best way to do this is to keep the
speaker cables short.
Good ventilation should also be provided around the
amplifier. The tubes generate a fair amount of heat, and
natural ventilation is necessary to dissipate this heat to the
surroundings. The amplifier chassis will get warm, but
should still be comfortable to touch.
Always place the amplifier on a firm, smooth surface.
Operation
Tube amplifiers need a load connected to their output.
Always connect the speakers before operating the
amplifier.
To power on:
 Flip the power switch UP to STANDBY.
LED glows ‘Red’.
 Wait 1 minute, for the tubes to heat up.
 Flip the power switch DOWN to OPERATE.
LED glows”Green”.
 Switch centre position is OFF.
When making or breaking any connections, always turn off
the power to the amplifier first, so that no hum or
transients are transferred to the speakers.
When sitting down to a listening session, it is a good idea
to let the system warm up for a half-hour. This stabilizes
the circuitry, and makes it sound better.