From Rain City Audio:
A customer recently brought me the guts from his Magnavox 1ST611R mid-century stereo console for an overhaul. He’d had the console for a while, working but with some trouble, but wanted to finally get it back to top shape for some more daily use. These are dual-chassis consoles, with the power amplifier and power supply on one chassis and the tuner/pre-amp on the second one, with a total of 13 tubes, including stereo push-pull 6V6s for the outputs. When properly adjusted, this amp produces about 10W per channel.
This one had been serviced a couple of times in the past, including the amplifier section where someone had replaced a pair of the coupling capacitors with new Orange Drops. Other than that, though, the repairs were still 40+ years old and were due for re-work.
Testing the resistors in the power supply and amplifier sections, they were drastically out of their tolerance, and one of the resistors in the feedback network on the voltage amp was damaged which would have prevented that side from demonstration proper gain. All but 4 resistors ended up being replaced in the amp section. The can cap was replaced with new under-chassis capacitors on a terminal strip as well.
A few of the tubes needed to be replaced; a 6AL5 had one diode giving no emissions, a 6V6 was very weak, and the 6CA4 rectifier tube was shorted. Instead of replacing it with another tube, though, the socket got covered up and the tube replaced with a pair of 1N4007 underneath. This also reduces the total power consumption of the unit by 6.3W, the tube’s heater. The additional B+ voltage due to the missing voltage drop inherent in the 6CA4 isn’t significant, either, as the 6CA4 already has the lowest forward voltage drop of all tube rectifiers and this system is by no means pushing the limits of any of its tubes.
Up in the tuner, there were two electrolytic capacitors in the chassis can, a pair of electrolytic capacitors in a common lead package for cathode bypass, and a small handful of paper caps which were replaced with film caps. Most of the resistors in this section tested in spec or close, but a few were replaced as well.
Testing everything out:
Time for an alignment!
Both AM and FM peaked up nicely to accurate dial tracking, and received FM distortion around 0.5% THD from starting off over 1.1%. Not too bad! Now for final listening tests, after replacing all 3 burnt out dial lamps:
Quite a few replaced parts! Three tubes, 5 paper caps replaced with film caps, 8 electrolytic capacitors, 3 dial lamps, and 20 resistors to get this console back to nearly-new condition.
The owner reported that he got it home, installed back in the cabinet, and it sounds fantastic streaming audio from his Chromecast. All done!
What a timely project! I have had one of these 88-02-00 Magnavox amps for years. I have recently purchased another one on E-bay and recently purchased the tuner section. This article makes my day for sure. Thanks, Robert P
Thanks J.W. ! I really enjoyed this post. You put in so much effort. It shows.