k7iou
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« on: April 22, 2015, 11:19:24 PM » |
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I thought I would share how not to repair a leaky mod tranny. I was very slight and the rubber seals were degraded. I was advised to trim out the degraded rubber with an exacto knife and clean with carburetor cleaner. Looked good, but the mistake I made was using Permatex The Right Stuff. Let it cure a day and installed it. Tripped the safety relay. Checked it with a Megger and primary's were shorted to case. Started looking for a replacement. Talked to a friend and he asked if I let it cure? Well on the outside it was but when I performed surgery with the knife it wasn't inside. Cleaned it all off, checked again and short to case was gone. So this time I was advised to use Teflon tape and wrap very tight at base of ceramic insulator. I researched silicon sealer and found on a Tesla Reactor website mention of only using clear 100% silicone sealer. If it works for their reactors it must be ok. So I added the clear silicone sealer and tested again. Then used a nitrile
Oring and slid it down to the gap at the base of the ceramic insulator. Baking a couple days in our AZ sun.
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Patrick J. / KD5OEI
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« Reply #1 on: April 22, 2015, 11:38:21 PM » |
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Hope it works. Please let us know the results of the repair. Looks lie it has a nice mount for a spark gap there.
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Radio Candelstein - Flagship Station of the NRK Radio Network.
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k7iou
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« Reply #2 on: April 22, 2015, 11:43:36 PM » |
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Yes, has a nice spark gap. This pic has the Permatex sealer which I removed.
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de k7iou
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ka1bwo
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« Reply #3 on: April 25, 2015, 12:10:23 AM » |
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I had a similar problem with a oil filled capacitor. I flipped the capacitor terminals
up to stop the oil weeping. Cleaned the insulators and case with Lacquer thinner. Applied JB weld neatly around the insulator were it meets the case. Let the epoxy cure for 24 hours. Hasn't leaked since the repair over a year ago.
Joe
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Patrick J. / KD5OEI
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« Reply #4 on: April 25, 2015, 10:10:33 AM » |
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If building, I always try to keep those terminals up. Suspicious of them because they are old.
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Radio Candelstein - Flagship Station of the NRK Radio Network.
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KA0HCP
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« Reply #5 on: April 25, 2015, 01:21:59 PM » |
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Well, it's not a surprise that 'aluminum colored" Permatex has aluminum flakes in it.
Metal reinforced JB Weld has iron particles.
"Caveat Electrician!"
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New callsign KA0HCP, ex-KB4QAA. Relocated to Kansas in April 2019.
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W2VW
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« Reply #6 on: April 25, 2015, 02:43:09 PM » |
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Many silicone RTV automotive type sealers contain filler.
The stuff without filler works very well for high voltage insulation.
Plain high heat orange or the old blue Permatex has repaired leaky high voltage situations to 7 kv for me in the past. The good insulating silicone has no body and feels like grease between the fingers when uncured.
Many rubber compounds do not insulate well at high tension or RF. Automotive radiator or heater hose makes a great dummy load.
RTV needs 24 hours to cure as mentioned by the op.
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W1RKW
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« Reply #7 on: April 25, 2015, 05:40:56 PM » |
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I agree on the RTV filler comment. I repaired a O'scope HV divider block to get it working with RTV. Only I had an RTV that was black on hand. It arced through the RTV. Someone suggested simply using clear. Scraped off the black stuff and went with GE clear vice Permatex. Let it cure for a couple of days and all has been good since.
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Bob
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k7iou
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« Reply #8 on: April 25, 2015, 07:35:15 PM » |
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Well it failed the load test. Found on #3 left carbon on Teflon tape and on oring. Cleaned it all off. Borrowed a fellow hams Hipot and tested the clear silicone up to 5kV ok. Tested oring ok. Tested Teflon tape ok. Tested the mod tranny in the dark & #3 @ 4 kV would start shorting from post to case. Wrapped it tightly with Teflon tape and tested, ok up to 5 kV. Removed tape installed a very small oring and tested ok. So I researched silicone sealers as plain black was suggested but it contained carbon black! So cleaned good installed clear GE Silicone II, the outside formula and a slightly tighter oring. Will let it cure in the sun a couple days and hipot again.
If it fails I will order the corona paste and brush it on, let it dry & hipot again. If that fails the porcelain cap must have a carbon trace where I can't get to it so I will crush it to remove it and use a spark plug boot as they are supposedly good to 50 kV.
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Jim, W5JO
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« Reply #9 on: April 25, 2015, 08:36:18 PM » |
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Metal reinforced JB Weld has iron particles.
"Caveat Electrician!"
JB WELD EPOXY STEEL HARDENER – 48008 Calcium Carbonate Barium Sulfate Magnesium Silicate Titanium Dioxide Zinc Sulfide Furfuryl Alcohol Polyamide Resin Aminophenols |
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W2VW
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« Reply #10 on: April 26, 2015, 05:23:04 AM » |
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I'd look for a way to remove the ceramic insulators for inspection. One probably has cracks.
Been there with a late BC-610 sealed xfmr.
Replaced the insulator with silicone and it held up until I found a scrap xfmr with good insulators to use.
I avoid ceramic insulators when building.
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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG
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« Reply #11 on: April 26, 2015, 11:10:46 AM » |
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Possibly the "O" rings are/were a problem?
The original way was to use fiber washers, afaik.
_-_-
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W2VW
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« Reply #12 on: April 27, 2015, 02:31:59 PM » |
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The O rings are of course between the case and ceramic insulator to seal oil in.
If the insulator has a carbon trace the O ring now takes on the job of insulator. Goobering over it may help but the root cause still exists.
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k7iou
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« Reply #13 on: April 27, 2015, 11:44:38 PM » |
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The GE Silicone II Clear and the orings did the job! Got it on the air today! Hurray!
In retrospect I should have left it alone BUT since it's in the house and contains PCB's I didn't want that kind of a leak in my home or shack.
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Steve - K4HX
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« Reply #14 on: April 27, 2015, 11:54:24 PM » |
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Congrats. I probably would have let it leak (lazy).  |
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KA0HCP
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« Reply #15 on: April 28, 2015, 09:29:16 AM » |
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Metal reinforced JB Weld has iron particles.
"Caveat Electrician!"
JB WELD EPOXY STEEL HARDENER – 48008 Calcium Carbonate Barium Sulfate Magnesium Silicate Titanium Dioxide Zinc Sulfide Furfuryl Alcohol Polyamide Resin Aminophenols So much for truth in advertising!  |
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New callsign KA0HCP, ex-KB4QAA. Relocated to Kansas in April 2019.
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k7iou
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Johnson Viking Five Hundred
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« Reply #16 on: April 29, 2015, 01:50:46 PM » |
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Metal reinforced JB Weld has iron particles.
"Caveat Electrician!"
JB WELD EPOXY STEEL HARDENER – 48008 Calcium Carbonate Barium Sulfate Magnesium Silicate Titanium Dioxide Zinc Sulfide Furfuryl Alcohol Polyamide Resin Aminophenols So much for truth in advertising! Barium sulfate is a heavy metal. Definition; a metal of relatively high density, or of high relative atomic weight. I'm sure it works fine for stopping a leak as long as the hi voltage tap is away from it. I've also heard that super glue gel works too. |
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de k7iou
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Jim, W5JO
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« Reply #17 on: April 29, 2015, 02:10:45 PM » |
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Metal reinforced JB Weld has iron particles.
"Caveat Electrician!"
JB WELD EPOXY STEEL HARDENER – 48008 Calcium Carbonate Barium Sulfate Magnesium Silicate Titanium Dioxide Zinc Sulfide Furfuryl Alcohol Polyamide Resin Aminophenols So much for truth in advertising! Barium sulfate is a heavy metal. Definition; a metal of relatively high density, or of high relative atomic weight. I'm sure it works fine for stopping a leak as long as the hi voltage tap is away from it. I've also heard that super glue gel works too. Be careful of the brand or type of super glue. Heat can do a number on it. |
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