AMI Model "K" Amp Page
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Our model "K" has a mono amp system. There is another phono cable provided for connection to the cartridge to expand to stereo. Here is the amp in "as found" condition:
Pre-amp Stage: 4, 12AX7/7025
Driver/Phase Inverter Stage: 2, 12AU7
Power Output: 2, 6973
Power Output: Approximately 16 Watts RMS
The amp was working, but we were getting feedback due to the pre-amp tubes vibrating with the sound, and the sound quality was not as good as we knew it could be. We removed the amp to replace old paper caps, clean tube sockets, and re-mount the pre-amp. The pre-amp is the smaller chassis to the right above, and is mounted with grommets to the main chassis to isolate the tubes from picking up noise transmitted through the chassis (tubes run at high gain can pick up audio or vibrations if they are not mechanically shock-isolated).
Here, we are beginning the re-cap job on the amp. The black caps with the colored bands are very prone to leakage (a decrease in resistance, which can change tube bias values and increase distortion). These caps are also prone to shorts.
Here is the amp, finished. We re-did the connections to the power cord...the cord had been replaced by a previous owner but the connections to the chassis were not soldered! We checked the electrolytic cans with the ESR meter and they looked OK, so we left them in. We sprayed the tube sockets with Dexoit DN5 and replaced the 1st stage pre-amp tube with a brand new 12AX7/7025.
Finally, the amp cleaned and re-installed in the jukebox.
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