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Old 31-12-18, 23:30
David Dunlop David Dunlop is offline
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Join Date: Feb 2006
Location: Winnipeg, MB
Posts: 3,384
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Over the past few days, I have been able to remove the damaged BAND and FREQUENCY ADJUST Switch panel from my Main Set Receiver and replace it with the undamaged one from the backup receiver. In the process, I also took the time to examine all the Valve Shields and Caps in the two units and apply the best of the lot to the Main Set receiver.

All this was not done without incident, however. The issue in this situation turned out to be the Band Selector Switch knob on the backup receiver. It simply did not want to come off the switch shaft and there was nothing at all to leverage against, other than the panel behind it that I needed…undamaged. I tried everything I could think of for the better part of an hour and a half and could only gain half the distance needed to get the knob off the shaft.

This turned out to be a VERY interesting little switch. It is actually mounted on a sub chassis on the right hand side on the main chassis assembly. The knob shaft passes through a small support collar on the switch panel and straight back about 3 inches to a support sleeve about an inch and a half long. Immediately behind this rear support, the shaft ends in a brass gear, part of a two gear right angle drive that feeds the selector action to the actual switch on the right hand side.

After studying this arrangement for a while, I realized I could loosen the grub screws on the rear support sleeve and brass gear on the end of the knob shaft and slide the entire shaft straight out the front of the panel. I could then remove the offending knob and reinstall the knob shaft. Almost.

Things proceeded well until I arrived at the last item: the brass gear on the end of the shaft. Seems the last dear soul who worked on this particular item did not feel the grub screw had been secured safely until the Bristo Key had been turned a sufficient number of times to completely round out the inside of the grub screw. And then the daft twit probably continued to turn the key further, while consuming a large pot of coffee! Sigh!

I really hated having to resort to it, but out came the hack saw and off came the front 1.5 inches of shaft with the offending knob still attached. Even in this new free state, I had to lock a pair of vice grips onto the shaft stub and gently lever the knob with a hammer claw to finally pop it from the shaft undamaged. Interestingly enough, after careful cleaning and inspection, this knob slipped quite happily onto any other shaft available, but did not want to go back on the piece of the one it had just been pried from.

I was feeling pretty bummed about having to trash an otherwise good shaft assembly, but when talking to a friend last evening, he advised he has a box full of NOS switch shafts and can easily enough find one I can use to replace the one I had to cut. I will just have to drill out the damaged grub screw from the brass gear, carefully, install a new grub screw and it should be good to go.

One other small discovery was that when I removed the outer most 12SC7 valve from the Crystal Calibrator, I discovered the central alignment pin was missing and the inner glass envelop stub was cracked. So that valve was clearly not working anymore. I found the pin stub still sitting inside the valve socket, fished it out and installed a new 12SC7.

David
Attached Thumbnails
WS No. 52 Receiver SN 6691 C.JPG   WS No. 52 Receiver SN 6691 D.JPG  
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