Tagged: Great pots afire !
April 28, 2020 at 6:52 pm #13967
Wow! That was freaky! I picked up the 2 tubes i required to finish overhauling my Hallicrafters S 38, Installed them and bench tested the radio. Worked great! Caps and Electrolytics replaced, all switches cleaned and lubricated and several lengths of crispy wires replaced and a handful of resistors. I put it back into it’s metal case and take it up to the master bedroom because I have a wire strung up and want to try the shortwave. I attach the radio to ground and hooked up the antenna wire. I turn the radio on and the lights dim in the room accompanied by a zapping sound and smoke pouring out of the radio. Continues to burn with flames after I turn it off and even after being unplugged, the fire continues to burn until i finally manage to huff and puff and it goes out. I carry it’s smoking carcass out of the master bedroom, down two flights of stairs and back into the shop. I run back upstairs and open all the windows in the master. On the way past my wife, I mention she may notice a really acrid smell in our bed room (and it isn’t my socks). Her eyes get wide and she asks me if it’s common for tube radios to spontaneously combust ? And I say no of course not, just a fluke. I pull it back apart and see that the on/off volume switch has had a major meltdown. Fortunately, the damage seems to be confined to only the switch without any shorted wiring anywhere else in the radio. The on/off vol switch did behave strangely before I cleaned it as the radio wouldn’t turn off. After giving it a good shot of cleaner,(2 days ago so it should have been dry inside) it seemed to work fine again. Can I assume because there is no burnt wiring leading to and from the switch that the problem rests with the switch itself? Possible mitigating circumstances. 1) It was the First time I added ground and there was a little bridge I didn’t spot from antenna (2) to ground (see pic). I doubt that could be a factor as there was no damaged wiring in that area. 2) It has failed grommets that may be there to isolate the metal case. (See pic) again, it didn’t burst into flames when I initially tested it. Thanks for your opinion in advance, Gary on fire in Montreal.
Attachments:April 29, 2020 at 5:29 am #13972Jean MarcotteForum Participant
Hi Gary, obviously an internal problem in the switch that caused a short to ground. No other harm inside the radio. You need to change the switch but you also need to modify the power supply to make this radio safe. Check this web site, it explains the procedure : http://www.geojohn.org/Radios/MyRadios/Safety.html.
JeanApril 29, 2020 at 6:06 am #13973Alistair ThomsonForum Participant
Don’t you just hate that! 🙂
Radiomuseum.org has a lot on the S38, including the pdf attached, which talks about AC hum causes, and mentions both the switch and the mounting grommets. It looks like the mounting grommets need to have almost perfect insulation otherwise hum develops at high DC resistance. If there’s a total short between the case and the chassis, then what happens probably depends on where you connected the ground. Where did you make that connection?
The antenna-to-ground strap is not the problem: that strap is used when you have a long-wire type of antenna. With a balanced antenna you would remove it.
Attachments:April 29, 2020 at 6:55 am #13975
Thanks so much for your comments and suggestions. I joined Radiomuseum and downloaded all the riders pages before starting. The radio was heavily modified before I got it and had disconnected wiring inside and some hillbilly repairs including a missing tube replaced by a set of resistors etc. I will get a polarized cord along with a fuse and follow the diagram to make the radio safe. I was never a fan of metal cabinet radios in the past for this reason. Today, I will “jump” the switch to make sure the rest of the radio survived and go through my stock of pots and see if I can match something up.
Thanks for all your help guys, Gary in Montreal.April 29, 2020 at 8:21 am #13977John GreenlandCVRS Member
One of these may be what you need. They are a 2 wire GFI style plug. I find them at surplus places and 2nd hand stores on various types hair dryers and straightners.
Interesting article on them here – https://people.ohio.edu/postr/bapix/GFCI_.htm
Attachments:April 29, 2020 at 8:39 am #13983
That’s a great all in one solution! I will go with that. Thanks for the link. It speaks volumes That 2 of the radios pictured are Hallicrafters and 1 is a S38!!
I had to jump on the radio this morning as I had to know if there was any collateral damage. Found a NOS pot in my stash and cut the shaft to fit.
Replaced the pot and all the adjacent wiring that got crispy. Radio plays great ! What a relief. I will mount a separate toggle for the on/off. Time to play (safely) outside. A rare nice sunny and warm day in Montreal and too nice to spend in the radio cave.
Attachments:May 2, 2020 at 4:44 pm #14120Gordon DannCVRS Member
we men never make mistakes –it must have be the wife’s fault — I’m safe my wife doesn’t read the radio stuff. cheers GordonMay 4, 2020 at 7:46 pm #14197
Still waiting on the new decals and the paint still needs to be refreshed on the Housing. it’s back together for now and I’m testing it out on an antenna. On the AM band, I’m good to go above and including 800, but below that where I know there are other AM stations, I just get a weeooooweee kind of sound when I use the tuner. With pretty much everything checked or changed, does that indicate the radio needs aligning? The schematics from Radiomuseum are pretty hard to read when it comes to the alignment procedure and I am waiting for a copy of the owners/installation manual with schematics that I ordered to arrive. Is what I’m describing likely an alignment issue?
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