Before aligning a Hallicrafters S-40, I used Caig Deoxit R5 to clean the very touchy bandswitch. No more intermittent contact - but "crackling static" immediately increased (I hadn't noticed much static before the cleaning) - but probably due to B+ beginning to find a path across the phenolic bandswitch wafer which switches transformer primaries on the RF amplifier plate, because within a few minutes, it started arcing on that wafer, and now arcs and starts a tiny fire every time you power it up. This wafer carries nearly 300 V. Has anyone had the direct experience of a bandswitch phenolic wafer failing this way (leaking high voltage / arcing a track into the phenolic) right after applying Caig, or any other contact cleaner? I don't recall any warnings - so I was hesitant to believe it was related, but sure is a coincidence the phenolic would track and arc and burn after 50 years as soon as I applied a cleaner.

By the way, among my repair options: 1) With a lot of work, I could reverse this RF output wafer with the identical RF input wafer, which is not loaded with B+; 2) or I could put a couple of .1 uF ceramic capacitors to the wipers on the other side of the affected wafer to DC isolate it (unless the arc-track grows so far that it reaches the grounded shaft!), this side goes to the mixer input and will slightly skew the tracking; 3) or I could capacitively couple the finicky 6SG7 RF amp output to the bad bandswitch and alter it to get B+ through a new resistor; or 4) wait around till a replacement wafer turns up somehow, or a junk S-40.
The bad wafer has a burned black spot on the center-disc portion, and 7 M ohms resistance between the 2 wipers on the opposite sides, but no visible black on the outer phenolic ring that carries the stationary contacts. The arc-track seems established now so that it will arc as soon as you power it up. Other suggestions? And is there a rule anywhere that you have to let contact cleaner dry before powering up the set? Did the cleaner just "activate" some grime and let an arc-track develope?

The only time I remember repairing a wafer switch I had to use a Dremel tool and a small bit to get in a etch away some of the phenolic wafer that had become conductive because of arcing. You may have to dig a hole clear thru. As far as I know, De-oxit is not conductive; you had this problem before cleaning. The switch I repaired was on a Hammarlund. Before aligning a Hallicrafters S-40, I used Caig Deoxit R5 to clean the very touchy bandswitch. No more intermittent contact - but "crackling static" immediately increased (I hadn't noticed much static before the cleaning) - but probably due to B+ beginning to find a path across the phenolic bandswitch wafer which switches transformer primaries on the RF amplifier plate, because within a few minutes, it started arcing on that wafer, and now arcs and starts a tiny fire every time you power it up. This wafer carries nearly 300 V. Has anyone had the direct experience of a bandswitch phenolic wafer failing this way (leaking high voltage / arcing a track into the phenolic) right after applying Caig, or any other contact cleaner? I don't recall any warnings - so I was hesitant to believe it was related, but sure is a coincidence the phenolic would track and arc and burn after 50 years as soon as I applied a cleaner.
:
:By the way, among my repair options: 1) With a lot of work, I could reverse this RF output wafer with the identical RF input wafer, which is not loaded with B+; 2) or I could put a couple of .1 uF ceramic capacitors to the wipers on the other side of the affected wafer to DC isolate it (unless the arc-track grows so far that it reaches the grounded shaft!), this side goes to the mixer input and will slightly skew the tracking; 3) or I could capacitively couple the finicky 6SG7 RF amp output to the bad bandswitch and alter it to get B+ through a new resistor; or 4) wait around till a replacement wafer turns up somehow, or a junk S-40.
:The bad wafer has a burned black spot on the center-disc portion, and 7 M ohms resistance between the 2 wipers on the opposite sides, but no visible black on the outer phenolic ring that carries the stationary contacts. The arc-track seems established now so that it will arc as soon as you power it up. Other suggestions? And is there a rule anywhere that you have to let contact cleaner dry before powering up the set? Did the cleaner just "activate" some grime and let an arc-track develope?

Part of your problem was in using De-oxit D5 which contains a slow evaporating flammable solvent which can be absorbed by the phenolic wafer material. This is a bad thing, and the solvent cannot fully evaporate. Hence it is NOT recommended for any energized circuits. Instead use their DeoxIT 100% spray or the DN5 which do not contain any flammable solvents. See the link: http://store.caig.com/s.nl/sc.12/category.9/ctype.KB/it.I/id.703/KB.215/.f for more information.
Steve

:Before aligning a Hallicrafters S-40, I used Caig Deoxit R5 to clean the very touchy bandswitch. No more intermittent contact - but "crackling static" immediately increased (I hadn't noticed much static before the cleaning) - but probably due to B+ beginning to find a path across the phenolic bandswitch wafer which switches transformer primaries on the RF amplifier plate, because within a few minutes, it started arcing on that wafer, and now arcs and starts a tiny fire every time you power it up. This wafer carries nearly 300 V. Has anyone had the direct experience of a bandswitch phenolic wafer failing this way (leaking high voltage / arcing a track into the phenolic) right after applying Caig, or any other contact cleaner? I don't recall any warnings - so I was hesitant to believe it was related, but sure is a coincidence the phenolic would track and arc and burn after 50 years as soon as I applied a cleaner.
:
:By the way, among my repair options: 1) With a lot of work, I could reverse this RF output wafer with the identical RF input wafer, which is not loaded with B+; 2) or I could put a couple of .1 uF ceramic capacitors to the wipers on the other side of the affected wafer to DC isolate it (unless the arc-track grows so far that it reaches the grounded shaft!), this side goes to the mixer input and will slightly skew the tracking; 3) or I could capacitively couple the finicky 6SG7 RF amp output to the bad bandswitch and alter it to get B+ through a new resistor; or 4) wait around till a replacement wafer turns up somehow, or a junk S-40.
:The bad wafer has a burned black spot on the center-disc portion, and 7 M ohms resistance between the 2 wipers on the opposite sides, but no visible black on the outer phenolic ring that carries the stationary contacts. The arc-track seems established now so that it will arc as soon as you power it up. Other suggestions? And is there a rule anywhere that you have to let contact cleaner dry before powering up the set? Did the cleaner just "activate" some grime and let an arc-track develope?

Once you start a carbon trail, though, you either have to scrape it away very well, or you have to replace the switch. You say that another wafer on the switch is interchangable, so switch them if you can. If they have different contact patterns, though, you cannot. I had this arcing problem with my EICO 625 tube tester. I replaced the selector switch with a porcelain one. Much better.

If I all-out clean a switch, I unwire it from the set. Then I take a toothbrush and some mineral spirits and clean away all of the gunk. Then I take the same toothbrush and some dish or laundry detergent and scrub in hot water. Then I let it dry for a day or so....you can dry in sunlight if you wish. If you wish to have bright contacts, you can polish them with brasso before washing in soap and water.

Thomas

Eddie,I f you find that you need to replace the wafer switch,get in contact with Gary Brown here:
http://tubes_tubes_tubes.tripod.com/index.html
He has a lot of Hallicrafters parts.I would know for I have an s-40a that has been a royal pain in the ass for the past six months.I think I have spent enough money on his parts to put braces on 3 of his kids if he has any.He is a nice guy and his prices are very reasonable.He will not sell you just the wafer switch however,you have to purchase tranformer coils,bracket,wafer and all,but the last unit I just purchased was only 12 bucks.I would say that was fair considering another joker I contacted wanted $100 dollars for the same pieces!!!!If all else fails,I may consider parting with one of mine.I needed the transformers not the wafer.But I will have to see this project through to completion before I will sell spare parts,and brother from what I've seen so far,radio broadcasting will be all digital before this rig ever gets straightened out.Please let us know how you make out.Good luck!

Eddie, get a good light on the subject and carefully scrape away all the carbonization. Clean all with alcohol and Q-tips. Then apply gentle heat to the switch by placing a lamp several inches away from it and keep it warm for a couple of days to drive out any of the solvent. Then you could carefully build up the scraped area with clear silicone using a toothpick, and again let dry with heat for a day. I stopped a TV high-voltage tripler from arcing over by cleaning up and then siliconing. Keep the silicone off metal parts since it contains acetic acid and can cause corrosion. There is a special silicone made for the purpose but I did not have any so used widely available consumer-grade product.