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 Post subject: Hallicrafters SX-43 restoration
PostPosted: Jul Fri 16, 2021 2:27 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10756
Location: Beaver Falls, PA. USA
I'm doing electronic restoration on one of these, for a club member. Lots of work, replacing resistors and capacitors; I do have a replacement electrolytic capacitor can on order from Hayseed Hamfest. It looks like I will have to pull the RF section to get at the components buried under there.

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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Jul Sat 17, 2021 1:11 am 
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Joined: Mar Thu 04, 2010 3:09 am
Posts: 127
It was difficult but I was able to get to all of them. In tight spots I used the cheap yellow caps as they were easier to work into the snug spots. Radio works great. While I was in there I undid many of the mods a previous owner had done to get it back to original as possible. Just be patient. This radio is worth the effort.

As to the filter caps, I left the original cans on top to maintain the original appearance and used single caps below. Plenty of room to do that and much less expensive.

Rich


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Jul Sat 17, 2021 3:37 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Monterey California USA
I have always managed it without doing so. There is that varmint mica capacitor across the 7F8 that is usually bad by now and makes the thunderstorm noises. It will work without it but it can be replaced with suitable tools and patience.

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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Jul Tue 20, 2021 1:40 pm 
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Location: Beaver Falls, PA. USA
It has been interesting, finding and backing out the various modifications. The previous owner evidently did not have a schematic, and he must have had some shorted capacitors which burned up some resistors. He replaced a 1k 1 watt with a 300 ohm 10 watt, a 3.3k with a 390 ohm, and another 3.3k with a 100 ohm. The work was done so long ago that the replacement caps were Mallory "Gems", and Sprague Black Beauties with yellow printing. He also replaced the volume control with a 5 megohm, and added a 560k resistor from the slider to ground. The new control had no AC switch, so he repurposed the tone switch for it, leaving the tone control wiring hanging in mid air. The 6SG7 first IF tube has been replaced by a 6SH7. I got the new electrolytic capacitor from Hayseed, and it is already installed. So far, 90 percent of the original resistors have measured off value. More to come!

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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Jul Wed 21, 2021 11:27 am 
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Joined: Aug Wed 14, 2019 6:56 am
Posts: 326
Location: angeles city.philippines,2009
you would be well advised to replace c53 thats on pin 6 of the 7f8 tube. it will give trouble in fm and has been mentioned here. it drove me nuts finding it. if you opt to replace it cut the lead NEXT TO THE CAP BODY,as it will be easiest to solder with an elongated soldering tip using the stub to accept the new caps coiled end. to get at the other end pull the main dial and the front panel. theres a cover that provides bearing support and closes off the housing that holds the band switch, theres a terminal board that mounts the c53's other end. initially i just cut it and the radio played as normal. it ate at me and i eventually replaced it. ive read that SOME 7f8's require that cap while others dont, its lost to history now i think. and you are quite right about the resistors. also the selectivity switch should be looked at theres B+ on on switch terminal that carries to the center wiper. unfortunately theres a rivet that mounts a GROUND on the other side thats not more than a 32nd of an inch away its easy for it to carbon track and start burning up the center element . i had to mine mine out and fill it with epoxy. before it goes dead short it will burn up the resistor that goes to the wirewound 's' meter adjustment. but before it does that it fries the "s" meter.. just what happened in mine which plays nicely now.


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Jul Wed 21, 2021 1:37 pm 
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Location: Beaver Falls, PA. USA
I have already pulled the front panel and dials. I need to restring the dial cord for the main tuning capacitor, and am working on the dial light wiring, which is crumbling.

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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Jul Mon 26, 2021 2:04 pm 
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Location: Beaver Falls, PA. USA
More progress! I have pulled the trimmer assemblies and the front end assembly. Many of the resistors in there were way off value, and there are a few mica capacitors which have to come out, including C53. I have a big stock of parts, and the alignment instructions, so I am all set. The worst one was the 1k cathode resistor for one section of the 7F8, which had risen to 2.3k. The one end disappeared under the bandswitch, and the terminal was not accessible. I cut it out, and used a "quig" to make the connection. The 68 ohm cathode resistor for the 6BA6 had risen to 175 ohms!

I will be sure to check the selectivity switch, once that I get the front end reassembled.

Edit: Front end is done, with all new resistors, and a couple of new mica capacitors. It's now remounted in the main chassis, and is being rewired.

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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Wed 04, 2021 2:39 pm 
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Location: Beaver Falls, PA. USA
The front end and bandswitch are rewired, and the trimmer decks are reinstalled. Both dial cords have been restrung, and all three dial lamp sockets have been rewired. The new volume control has been installed, along with the AC switch wiring. Soon, it will be time to power the thing up.

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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Fri 13, 2021 2:19 am 
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Joined: Aug Wed 14, 2019 6:56 am
Posts: 326
Location: angeles city.philippines,2009
you will want to change the mica cap in the fm detector.


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Sun 15, 2021 11:15 pm 
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Location: Beaver Falls, PA. USA
Thanks for the tip on the selectivity switch; mine was shorting out! I removed the switch, and was able to clean out the carbon tracks; I used a small cutter bit in the Dremel to widen the clearance a little. It now checks OK on the Telohmike leakage test.

I have been through all of the mica capacitors, and found a few leaky ones.

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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Mon 16, 2021 10:49 am 
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Joined: Aug Wed 14, 2019 6:56 am
Posts: 326
Location: angeles city.philippines,2009
did the 300 ohm resistor fry along with the "S" meter??? those meters hard to find, it might be better to fill the excavation with epoxy, i wouldnt use jb weld as it has carbon black in it, but my fears about it might be unfounded


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Tue 17, 2021 3:20 am 
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Posts: 10756
Location: Beaver Falls, PA. USA
The S-meter seems to be fine. I filled the cuts in the rotor with clear epoxy; just waiting for it to set up.

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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Wed 18, 2021 10:19 am 
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Joined: Aug Wed 14, 2019 6:56 am
Posts: 326
Location: angeles city.philippines,2009
tell me,does yours have the original bfo knob? if so is the knob special and have an 1/8'' bore with the rotation stop pin in the knob body or does it have a shaft adapter?


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Sat 21, 2021 8:55 pm 
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Location: Beaver Falls, PA. USA
It's alive! I just started the alignment. The 10.7 mhz transformers were way off frequency, but are done, and I am working on the 455 kHz alignment. I have to go through it again, to make sure that I have it right on the crystal frequency. The AM and FM broadcast bands do work, although the AM falls out at the lower end of the band; I have a couple of 7F8 tubes to try. I haven't progressed to the front end alignment yet.

I will have to look at the BFO knob; I am sure that it is original.

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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Sun 22, 2021 10:48 am 
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Joined: Aug Wed 14, 2019 6:56 am
Posts: 326
Location: angeles city.philippines,2009
its a personal choice but i just changed the output transformer to a hammond with a 4-8 ohm impedance output so i could use it on modern speakers. i originally used a matching transformer in an ancient pioneer speaker cabinet that had a AES guitar amp speaker installed that was 4 ohms. the same speaker with the matching transformer removed to my ears sounds much better. and the tone switch STILL functions. thats not much of a speaker set up and i imagine the sound will improve even more when i try the set on a modern 8 ohm speaker.mine sounds pretty good for an ancient single ended 6v6 tube. but just as some folks wouldnt dream of putting juice brakes in their restored model t i imagine there are those that wouldnt entertain the output transformer change either but i just got sick and tired of having to have a dedicated speaker for that set. yes please do check that knob for me you will need to remove it anyway to zero the bfo. i had to scrounge a knob and modify an adapter i got on ebay. those things seem to be always missing like my sx99 was when the bfo gets out of wack the knob gets removed and disappears. there must be a special hiding place on the planet where that style of bfo knob goes never to be seen by humans again as i sure couldnt find one


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Sun 22, 2021 10:57 am 
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Joined: Aug Wed 14, 2019 6:56 am
Posts: 326
Location: angeles city.philippines,2009
i know it sounds like witch craft but i had over 2 mhz of fm drift. i finally removed that first ceramic trimmer(range) and scrubbed it in lacquer thinner after a thorough cleaning in deoxit d100 to get the silver tarnish off.im not really certain why it worked but now its only .5 mhz of drift. i am not a radio expert but i sure do like fixing them.


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Sun 22, 2021 3:00 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10756
Location: Beaver Falls, PA. USA
The radio did come with the original 600 ohm speaker, a rare find. I did have to replace the equalization slide switch, and the capacitors associated with it; I made up a long cable, so the speaker can sit next to the bench, while I am working on the set.

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Tim KA3JRT


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Tue 24, 2021 1:44 am 
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Location: Beaver Falls, PA. USA
Slogging through the alignment procedure... I have the AM broadcast and FM broadcast bands working fairly well, and have band 2 pretty close; both it and the FM band are off a little on the low end, and I can't get them any closer. The instructions do not specify where the dials have to be set, with regards to the position of the variable capacitors, so I may have to "fudge" things a little. Since I had both dials off to do the restoration, it is possible that they need to be moved.

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Tim KA3JRT


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Tue 24, 2021 5:43 am 
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Joined: Aug Wed 14, 2019 6:56 am
Posts: 326
Location: angeles city.philippines,2009
i never could get FM tracking exact either and just let the lower bands be off as i dont spend any time down there. NO amount of back and forth would solve it. moving the low side only shifted the high side,and believe me i gave it some time. its enough to be annoying though. in truth it begs the question of how good were they when new?? i had no trouble with the rest. i dont remember how band 5 went as its been a while. however at least in this country theres absolutely nothing on it here.its not the radio either as my sx42 and 62 have zip too. interstingly my 42 and 62 had the same issue with tracking as well. its really quite a disappointment really with what i can get to listen to,as theres almost nothing in english and the chinese are everywhere. the australian broadcast co. ceased a few years back and the chinese took their frequency. they also like to block the BBC with ''fire dragon music''. but i do digress .


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 Post subject: Re: Hallicrafters SX-43 restoration
PostPosted: Aug Wed 25, 2021 9:31 pm 
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Location: Beaver Falls, PA. USA
It's about done! :D

As usual, the original alignment instructions for the FM IF and discriminator transformers were not good enough, and I had to perform sweep alignment to get them to come out right. The FM is surprisingly good for a 73 year old radio.

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