The attached service note is provided by H.H. Bloom, of SoundMaster Ltd., for more than 60 years a highly respected builder of audio equipment based in Ottawa, Canada. Mr. Bloom was recently asked to diagnose an issue with a Stereo 50 and, following analysis of circuits for the Stereo 20, Stereo 50, and Stereo 60, offers the following information for others who may encounter similar issues. SERVICE NOTE RE: LEAK STEREO AMPLIFIERS - 20, 50, 60 MODELS In all the diagrams for the above-noted models, there are two capacitors, one marked "C5R" for the right side, and the other marked "C5L" for the left side. Each capacitor is .02 MFD - 350 WVDC and is located in the phase inverter circuit of the 12AX7 tube. These capacitors are prone to developing a very unusual high resistance leakage, which can be only detected above the range of most ohm meters. The leakage resistance still allows the amplifier to function with noticable distortion on an oscilloscope connected to the speaker terminals because it destroys the equal audio drive going to the input grids of the output tubes. The recommended solution is to replace the said capacitors with ones having a voltage rating of 630 WVDC. The above-noted situation was found in a Stereo 50. H.H. Bloom Soundmaster Ltd.