Thordarson T-32W00 P1 u g - i n - P r e - Amp 1 i f i e r and Equalizer Stage for Magnetic Pick-up Cartridges
This small self-contained plug-in pre-amplifier is an accessory unit designed for use with Thordarson T-32W10 10 watt Phono-Tuner amplifier or any other audio amplifier or radio set where magnetic operation is desired. ! This unit, employing a minature 12AT7 twin triode tube, provides the additional voltage amplification and bass equalization necessary when employing a magnetic reluctance phono pickup cartridge.
The T-32W10 amplifier chassis socket which receives the plug-in pre-amp has been pre-wired at the factory. No additional wiring operations are required to employ a magnetic pickup with this amplifier. To add the pre-amp to other equipment it is necessary to mount an octal socket on the chassis and wire to it the supply voltage loads and signal connections.
The bass equalization provided by this pre-amp is adequate for all popular magnetic reluctance phono pickups. A maximum bass boost of 15 db occurs at 100 cycles; The frequency response from 1000 cycles out to 20,000 cycles is flat within ± 2 db.
The maximum signal that can be applied to the pre-amp at 1000 cycles is approximately 100 millivolts. To employ a magnetic pickup having a greater rated output will require the use of a voltage divided network to attenuate the signal. This can be readily accomplished by connecting a l/z watt resistor of the proper value in series with the input load. For example, if the output of the pickup is rated at .5 volts, connect a 4 megohm resistor in series with the input load. Since the input resistance of the pre-amp is 1 megohm, this will apply one fifth the voltage, or 100 millivolts to the preamplifier.
The plug-in pre-amplifier also finds application as a microphone pre-amp stage for use with T-32W10 phono amplifier or other medium gain amplifiers to provide the necessary gain when high impedance crystal or dynamic microphone operation is desired. For this service the pre-amp base pins #4 and #5 are joined together this removes the bass equalization making the response essentially flat from 50 to 20,000 cycles. The voltage gain under this condition of operation is 38 db at 1000 cycles.
To employ the pre-amplifier with the Thordarson T-32W10 Tuner-Phono amplifier, refer to the instruction sheet which accompanies this unit.
T-32W10 10 Watt Tuner
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