Tandberg 1200X click and pop fix

The Tandberg 1200X reel-to-reel recorder record-playback-amp switches exhibit loud pops and clicks in the audio channel when the switches get old and worn. This video discusses the cause for this and a solution (apart from giving the contacts a good clean with a good contact cleaner). There are a couple of inaccuracies in the audio commentary (it was a while since I did the modification so I'd forgotten some of the details when I made the video), but the end result is the same. The modification is described as modifications to the schematics and PCB layout in http://butoba.net/downloads/TB1200X-s... and http://butoba.net/downloads/TB1200X-p... . (However, please note that the schematics modification includes a 3k9 resistor across the left volume control which was necessary on my particular machine to equalize the playback levels between the left and right channels, but should not be necessary on other machines).