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Hallicrafters SX-42 rust issue




 
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Author Topic: Hallicrafters SX-42 rust issue  (Read 1377 times)
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k7mdo
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« on: May 12, 2021, 04:29:59 PM »

I just recently acquired a really good looking SX-42.... except for one thing, a mouse had built a nest in and around the 6V6 output tubes and power transformer.  This set, otherwise, is in great shape.... pretty much original underneath and in the tuning system.

I would like to restore it but am not sure how to address the rust without further damage.

One thought I have had is to wire brush it off (not my first inclination) and the most recent thought is to mask and bead blast the area.  I have the equipment to do the bead blasting but haven't yet decided if it is a good idea or for that matter, what medium to use in the bead blaster.

BTW the serial number is HA-63404 and I have not found a date of assembly but all the labels are intact.

Any thoughts on my idea or alternatives would be appreciated.



* SX-42 front.JPG (40.11 KB, 666x375 - viewed 161 times.)

* SX-42 rust.JPG (51.36 KB, 666x375 - viewed 231 times.)
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Scott SWL
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« Reply #1 on: May 12, 2021, 07:04:24 PM »

I have never tried it, but naval jelly is supposed to work on rust.
I have used a wire brush, and scraper to remove similar rust.
The transformer shell could be removed and blasted pretty easily, and removing it would make cleaning the chassis easier.
I would be a little hesitant to blast the chassis, as the media could get in some bad places.
There are some paints that blend well with the chassis plating.
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Tube Audio,Shortwave, Computers programming Raspberry Pi, Drones.
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k7mdo
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« Reply #2 on: July 23, 2021, 11:06:25 AM »

Dremel tool with tiny wire brushes got most of surface cleaned.  The  pitting will just have to stay. 

After a lot of cleaning underneath and replacement of weeping capacitors I have it playing well on the AM/CW bands through 30 mHz but.... FM is pretty much deaf.

The "mechanics" of the tuning and dials was a challenge but the real job was replacing the dial cords. I used to do a lot of watch repair and without that patience and tools am not sure if I would have been successful!

73 Tom
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Jim, W5JO
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« Reply #3 on: July 23, 2021, 11:20:48 AM »

On the FM band the antenna seems to make a difference in the reception of signals.  I use a 135 ft. inverted L and it received quite well on bands 5 & 6.  I tried constructing a dipole for it and it made no difference in the signal levels.  But using my 80 meter dipole it is almost deaf.  What does your signal generator say?
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WB6NVH
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« Reply #4 on: July 25, 2021, 02:07:50 PM »

The VHF FM band seems affected by the mica capacitors in the IF and discriminator cans and general opinion today is that you need to change them all out as a matter of course.  The postage stamp things.  It is over 70 years old and they seem to be suspect now.

I am pondering cleaning up rusty chassis by soda blasting.  There is also a new process that uses dry ice.  Those leave no nasty grit residue and soda washes out.  Not sure about effect on rust.  The next issue is that where there is rust or you clean the chassis to shiny condition, you are down to bare metal and have removed the cadmium plating.  It's not practical to re-plate with cadmium anymore but Caswell Electroplating has or had a kit that is supposed to be tin or something that looks much like original cad plating.  Cadmium is toxic and you don't want to breathe the dust from cleaning the chassis (or get Hanta virus from the mouse residue.)
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Geoff Fors
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Jim, W5JO
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« Reply #5 on: July 25, 2021, 04:43:52 PM »

The VHF FM band seems affected by the mica capacitors in the IF and discriminator cans and general opinion today is that you need to change them all out as a matter of course.  The postage stamp things.  It is over 70 years old and they seem to be suspect now.


If during alignment the IF cans have a good peak as they should I leave them alone.  However if the peak is broad or on one end of the coil or the other, you will probably find bad caps.  I have changed the caps in the IF cans of an SX 42 and it requires a steady hand and is not easy.  They use the end of the capacitors as tie points for the coil windings in most cases.

Good light and a steady hand is required.  Also for size, I suggest anyone look for 1 KV capacitors rather than the 500 volt versions to fit the bracket in place of those in the can.  If you cannot find or have them, 1 suggest you get some insulation tubing to cover the leads in the necessary places.
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K4RT
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« Reply #6 on: July 26, 2021, 09:03:11 PM »

Dremel tool with tiny wire brushes got most of surface cleaned.  The  pitting will just have to stay.  

Thanks for the update. Any photos of the finished chassis work? After cleaning off the rust did you apply anything to the treated area?
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k7mdo
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« Reply #7 on: July 28, 2021, 11:20:05 PM »

In regard to the note about antenna making a difference on FM,  absolutely.  I installed a small FM frequency range dipole and immediately got stations....  a little more alignment and I think the set will be working on all bands and all modes.

As to the "rust" issue, I was able to remove the rust with the Dremel tool but held short of a media sandblast to "fog" the area....  this is not pretty but the rust is gone and whoever gets the radio next can move forward with the restoration.  80 lbs is just too heavy for my radio bench to survive.

I think the worst problem for potential owners is not just the weight but also the 500 ohm audio output.  I have and use a dedicated transformer to 8 ohms and it is fine but I doubt most people have one anymore.  Out west here there is just not the plethora of things like that floating around.

We have just this last weekend had our first "tailgate" ham sale since the virus.  Another is proposed for October but still up in the air. 

73, Tom


* Rust removed.JPG (4085 KB, 666x375 - viewed 88 times.)
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K4RT
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« Reply #8 on: July 29, 2021, 12:07:06 AM »

Tom,

Thanks for posting the photo. Nice work. I've got a receiver chassis with similar rust. I'll try the Dremel treatment on it.

73,
Brad
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