APH-1050 Power Amplifier

If 40 watts RMS from 20Hz to 30KHz +/-1. 5 db sounds good to you, then you might enjoy this experiment. The most significant problem with public address gear is the use of audio output transformers which do not have enough iron in them to handle the lower frequency content at the amplifier`s full rated power. Look for amplifiers in which the output
APH-1050 Power Amplifier - schematic

transformer is as large as the power transformer. The bigger the better! Another problem with the output transformers is that the laminations are often fairly thick. Many thin laminations are preferrable to fewer thick ones. The laminations should be much thinner than those of the power transformer. If the transformer has a 25V balanced line output winding, then it can then be used to provide power feedback to the cathodes of the output tubes, which will abate a multitude of evils. Don`t be too picky, remember, these are PA amplifiers! Just try to find a pair if you want stereo. The output transformer is actually larger than the power transformer, and the output transformer also has a 70&25V. C. T. "line" winding as well as the 4/8/16 ohm "speaker" winding. Changes to be made can include different tube types, power supply voltages, and biasing/balancing arrangements. Since the Stromberg-Carlson APH-1050 can use most of these changes, It will be specifically discussed. In case you may have doubts, see what one very discerning music lover had to say about the four of these amps I modified specially for him, according to this exact Article. "The amps are the best electonics purchase I`ve ever made. They are absolutely reliable, do not get too hot, are low maintenance, have cheap replacement tubes (which I haven`t needed yet), and sound clean and quiet, with good bottom to the sound. They are a very good match for ar3a...

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