[Hallicrafters] SX-117 disaster

Sun Jul 31 23:46:04 EDT 2016

    I think the burned part is the end of the coil on a slightly larger 
former, perhaps meant to slide over the main former.  Heat could affect 
the slug, depending on what its made of but more likely has swollen or 
warped the former.  It doesn't look too bad.  If you can move the slug 
away from the cooked part see what the former looks like inside. Perhaps 
if its distorted a little you can straighten it with something like the 
end of a drill bit the right diameter.
    I had a worse case on an RCA AR-88 I rebuilt, two of the antenna 
coils had been heated to the point of distorting.  Both coils were wound 
on polystyrene formers so they melted pretty thoroughly.  I was lucky 
enough to be able to get two new ones from someone, I think in Oz land. 
My first indication that something was very wrong was when the slugs 
would not move. Since this former appears to be Bakelite its possible 
its not so bad, at least it would not melt. If the wire is still there 
and has not parted it may only be necessary to re-solder it at the 
terminals. Otherwise it must be rewound, not too big a job.  Either a 
repaired coil or new coil should get a dose of "Q-Dope". You can make 
your own by dissolving white polyfoam in Xylene or MEK.  Takes a while, 
it should be the consistency of honey. Polyfoam is pure polystyrene 
which has very low loss so it won't affect the Q of the coil.
     Good luck with the project, the SX-117 is well worth the effort to 
fix.

On 7/31/2016 7:33 PM, K9FFK wrote:
> Wow. L5 certainly did get hot but from the image I don't see any shorted
> turns, just missing enamel on some wire.
>
> Could RF heating change the properties of the slug?
>
> I wouldn't junk that coil just yet, though. The RF has to pass through
> L1A-C1 and by L1B-C2 to get to the L5 link.
>
> L1a-C1 and L1B-C2 are the 6.5 Mhz trap. How does L1 look?
>
> curious.
>
> Dick, K9FFK
>
>
> On 7/31/2016 7:26 PM, Jeff wrote:
>> Thanks to all the fast responses.  I've drowned my grief a bit, and I
>> did some disassembly.  The Antenna coil surely does look like it got
>> toasted.  I've included an image on my webserver:
>>
>>
>> http://www.podengo.com/sx117/L5.jpg
>>
>>
>> In looking at it, it looks as if the coil form actually deformed
>> (inside) so that the slug won't move past a certain point.  I don't
>> see any damage to rotary switches or other components.  The 6DC6s test
>> OK, but I don't have any replacements in my stock to try a different one.
>>
>> Anyone have any advice on the coil (or a spare you can part with?)
>>
>>
>> Jeff
>>
>>
>>
>> On 7/31/2016 3:05 PM, Jeff wrote:
>>> Looking for some advice or consolation...
>>>
>>> Previously well working SX-117/HT-44 twins.  I hadn't run them in a
>>> long time, and many cables got messed with in the mean time.
>>> Unfortunately, in my haste to hook the pair back up again, I got the
>>> transmitter output fed into the receiver antenna input...  and then
>>> hit transmit to tune up the transmitter...
>>>
>>> It's taken me a while to stop cursing about it, but now my SX-117 is
>>> deaf as a post.  A quick check of the RF amp and 1st mixer show that
>>> the tubes are OK.  A signal generator on 14.250 is barely audible,
>>> but I can no longer get a good strong peak on the preselector.  I can
>>> get a bit more of a peak on 40 meters, but it's still quite deaf.  I
>>> had the rigs in 20 meters when the mishap occurred.
>>>
>>> It's just about acting like there's no antenna at all hooked to it.
>>> I get no increase in noise whether or not it's hooked to the antenna
>>> or dummy load.
>>>
>>>
>>> I've had the courage to admit I've done something heroically stupid
>>> -- so I'm reaching out to the list for any thoughts or guidance as to
>>> how to fix this.
>>>
>>>
>>> Jeff
>>>
>>>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL