ROMANCE 50u-220 stereo Hi-Fi

Improving the sound of the 90U-2 LOMO cinema tube amplifier

At the moment, you can still buy inexpensive, tube mono amplifiers 90U-2, from the “Ukraine” film installation. This amplifier is not difficult to upgrade and obtain a very decent sound, high technical characteristics, which allows it to easily outperform many transistor amplifiers, both Russian and imported.

Note: I personally think that old equipment needs to be groomed and cherished, because there is less and less of it left. Therefore, it is better to create an amplifier from scratch than to break a factory receiver or amplifier for the sake of experiment; break it - don’t build it!

Konstantin

Factory diagram without modification

Specification

Transformer winding diagram

Modernization of the 90U-2 (push-pull) PP tube amplifier consists of reworking its circuit diagram (see the diagram below, click on it to get an enlarged size), transferring it to class A, removing general feedback, remaking the power supply, powering the filament of the input lamp constant stabilized voltage, manufacturing of the outer casing. The output transformer remains without modification.

Design: A closed-type push-pull two-stage tube amplifier (in a new housing) without negative feedback circuits is manufactured as a monoblock, with separate volume controls in each monoblock (channel). The input stage is implemented on 6N9S double triodes, the output stage on 6P3S pentodes, kenotron power supply. To obtain greater output power, it is recommended to install 6P3S-E output lamps (increasing Ia, decreasing the cathode resistor). It is preferable to use 6P3S lamps manufactured before 1985. Early tubes of the 6P3S octal series had gold-plated grids, which had a beneficial effect on the sound of the entire amplifier. New 6P3S-E lamps can dissipate more power, but the increase in power due to changes in the design of the anode in the direction of shortening it, winding a non-gold-plated mesh with a large pitch, worsened the sound properties of this beautiful lamp.

Features: The converted PP amplifier is designed for high-quality amplification of music programs from CD players. For high-quality sound reproduction, the PP amplifier requires speakers with a sensitivity of 90 dB/W. Very good results were obtained with highly sensitive acoustic systems based on modified cinema speakers.

Main technical characteristics of the upgraded push-pull tube amplifier 90U-2 LOMO, without feedback:
Nominal input voltage

Appearance of the converted amplifier 90U-2.

For questions regarding modernization, please contact us by email: [email protected]

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