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Old 18th Aug 2020, 9:12 pm   #41
Station X
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

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Originally Posted by mrrstrat View Post
Details on R27 from switch to where I found it. I can concur its about 5K.
R27 in my set is definitely colour coded 500R and measures around 500R. Either the value was changed at some point during the manufacturing cycle or it's an assembly error.

It's part of a switchable treble cut circuit with a 22nF cap in series. When I operate the switch all it seems to do is introduce some attenuation. I'll fit a 5k resistor and see what happens, or maybe try a bit of circuit analysis.
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Old 23rd Aug 2020, 4:37 am   #42
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

Sorry for not being here for a bit: been tied up for many days on projects. The SX-24 was bought a few days ago! I was hoping to have it around longer and was glad to offer a peak inside. I do have a SX-25 here too: how similar is it to the SX-24?
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Old 25th Aug 2020, 11:41 am   #43
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

It's OK mrrstrat, the set is working.

I'll experiment with the value of R27 and maybe plot some frequency response curves.
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Old 25th Aug 2020, 1:26 pm   #44
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

Time for some updates, as usual repair work has got ahead of my posting details here.

I checked all the resistors in the set comparing their specified value, color coded value and measured value. I also checked that they were installed in their correct electrical positions when compared to the circuit diagram.

I found some resistors missing, some resistors present which aren't shown on the circuit diagram, some resistors of the wrong value and finally a few resistors which had drifted way high in value. I'll document circuit changes etc. in a separate thread to aid any future restorers of these sets.

All the resistors which had gone excessively high in value were replaced. I expect that with use other resistors will drift high and need replacing.

I checked the primary and secondary windings of all the IFT's for continuity and they were OK.

In sorting out the S Meter wiring I discovered that the 500R zero setting pot in parallel with it was going open circuit when set near max. Drilling a hole in the casing and injecting some Servisol cured that. The HT supply to the RF amplifier valve is fed via this resistor so, with no S meter fitted, it's important that the pot has continuity. I have a couple of unrestored SX28's which I'll borrow a meter from later.

At this stage I was satisfied that everything was wired correctly and the set stood a good chance of working.
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Old 25th Aug 2020, 1:39 pm   #45
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

I had an SX28 push pull output transformer transformer with an open circuit primary winding which was the same size as the output transformer missing from this set.

Forum member Ed Dinning rewound it for me to the original spec with a 5000R secondary winding tapped at 500R. Why Hallicrafters decided to use these high impedances I don't know.

Before fitting the transformer to the chassis I scraped off the hideous gold paint from the chassis in the area where the transformer is fitted. I left some slack in the connecting leads so that I can lift the transformer enough to paint under it later.

Of course I also needed a 5000R speaker, so I made one using an 8" diameter 8 ohm speaker along with a 25:1 turns ratio transformer also supplied by Ed. This is how Hallicrafters made their own high impedance speakers.
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Old 25th Aug 2020, 2:06 pm   #46
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

I have used the T725 to solve my 500R and 5000R speaker blues:

http://makearadio.com/misc-stuff/t-725.php

At $8.00-$10.00 USD they are a deal.

Quote:
Originally Posted by Station X View Post
I had an SX28 push pull output transformer transformer with an open circuit primary winding which was the same size as the output transformer missing from this set.

Forum member Ed Dinning rewound it for me to the original spec with a 5000R secondary winding tapped at 500R. Why Hallicrafters decided to use these high impedances I don't know.

Before fitting the transformer to the chassis I scraped off the hideous gold paint from the chassis in the area where the transformer is fitted. I left some slack in the connecting leads so that I can lift the transformer enough to paint under it later.

Of course I also needed a 5000R speaker, so I made one using an 8" diameter 8 ohm speaker along with a 25:1 turns ratio transformer also supplied by Ed. This is how Hallicrafters made their own high impedance speakers.
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Old 25th Aug 2020, 2:08 pm   #47
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

With repairs complete, apart from the missing S Meter, it was time to see whether the set would work.

The high Z speaker and shack aerial were connected to the set. I felt sufficiently confident to apply mains directly without using a lamp limiter or Variac.

Once the valves had warmed up sound could be heard from the speaker, but no stations could be received on any waveband. In time honoured fashion I touched the wiper tag of the volume control and heard a loud buzz from the speaker. Similarly touching the top cap of the mixer valve produced a click from the speaker. Nothing when touching the aerial terminal though. There was obviously a fault in the RF and/or Local Oscillator stage.

Visual inspection of the two triple section tuning capacitors showed that the brass slip rings and wipers making the connection to the moving vanes were excessively "browned". Applying Servisol and moving the tuning controls from end stop to end stop several times fixed this and restored full operation with signals being received. The tuning caps are going to need a lot more cleaning. Apart from the rust they've also had that nasty gold paint applied to them and some of it has dripped onto the vanes. This receiver is never going to win a beauty contest.

Medium wave here is rich with transmissions and the set picked up all those I'm used to receiving. I gently adjusted the IFT trimmer screws, after carefully noting their positions. I wasn't able to make much improvement and all the trimmers peaked nicely with reserve travel either side of the peak. I hate trimmers which peak right at the end of their travel.

The set will be used as the workshop radio for a while to see if any faults develop in use.
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Old 9th Sep 2020, 2:53 pm   #48
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

The hideous gold/bronze paint which had been applied to the chassis was beginning to annoy me, so I spent the best of three afternoons scraping it off. All the while I was cursing whoever subjected this radio to such cruel and unusual punishment. The paint was so thick in places that it was still wet under the surface. They'd even painted over the valve holders, which are marked with the valve type, and painted parts of the tuning capacitors.

I'll rub down the chassis later, apply some rust treatment such as Jenolite, and give it a coat of grey zinc rich primer.

The band spread capacitor has obviously been removed to facilitate painting over the rust. The resoldering was poor and when I removed the end support brackets I discovered that a wire had dropped off the aerial tuning section. Resoldering this has increased the receiver's sensitivity and it now receives MW stations without an aerial connected. I may give the tuning capacitors the dishwasher treatment.
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Old 9th Sep 2020, 3:03 pm   #49
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

I restrung the slow motion drive to the band spread tuning capacitor as the original cord had been knotted half way along at some time. As usual I used Flyline Backing for this purpose. There is no threading diagram in the service manual, so I photographed and sketched the original arrangement before removing it.

The grub screws securing the drive pulley had chewed heads so I replaced them with cone point grub screws. Thread is UNC as on most US comms receivers, but I forget diameter and pitch.
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Old 9th Sep 2020, 4:45 pm   #50
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

Quote:
Originally Posted by Station X View Post
I had an SX28 push pull output transformer transformer with an open circuit primary winding which was the same size as the output transformer missing from this set.

Forum member Ed Dinning rewound it for me to the original spec with a 5000R secondary winding tapped at 500R. Why Hallicrafters decided to use these high impedances I don't know.

Before fitting the transformer to the chassis I scraped off the hideous gold paint from the chassis in the area where the transformer is fitted. I left some slack in the connecting leads so that I can lift the transformer enough to paint under it later.

Of course I also needed a 5000R speaker, so I made one using an 8" diameter 8 ohm speaker along with a 25:1 turns ratio transformer also supplied by Ed. This is how Hallicrafters made their own high impedance speakers.
Regarding the hideous gold paint, it seems like the export Hallicrafters receivers were painted with some form of a anti-fungus varnish.
The Hallicrafters receivers I'm familiar with, don't have it. Also, not much rust to deal with either.
Great restorations, a lot of attention to detail!
Dave, USradcoll1
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Old 10th Sep 2020, 12:32 pm   #51
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

I found no trace of anti-fungus varnish which I'm familiar with in tropicalised military sets.

I don't think I'll ever be able to claim that I've restored this set. I'll just have put it into good working order.
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Old 10th Sep 2020, 12:37 pm   #52
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

I checked out the resonant frequency of the receiver's 455kHz crystal by connecting it in series with a signal generator and a scope. Stepping the generator's output in 10Hz steps showed a clear peak at 455.42kHz.

The frequency of these crystals is nominal and not exactly 455kHz. The IF has to be aligned to the crystal frequency rather than 455kHz. This also applies to other receivers with single crystal filters such as the RCA AR88 and National HRO.
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Old 11th Sep 2020, 12:48 pm   #53
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

I think this guide is as good as it gets for restringing:

http://www.nucow.com/alldial.htm

No mention specifically to the SX-24 but darn near everything else.

Quote:
Originally Posted by Station X View Post
I restrung the slow motion drive to the band spread tuning capacitor as the original cord had been knotted half way along at some time. As usual I used Flyline Backing for this purpose. There is no threading diagram in the service manual, so I photographed and sketched the original arrangement before removing it.

The grub screws securing the drive pulley had chewed heads so I replaced them with cone point grub screws. Thread is UNC as on most US comms receivers, but I forget diameter and pitch.
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Old 11th Sep 2020, 12:49 pm   #54
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

I aligned my rebuilt SX-110 to the crystal as well: I was at 455 (and a slight amount of measrument noise) with my crystal as well


Quote:
Originally Posted by Station X View Post
I checked out the resonant frequency of the receiver's 455kHz crystal by connecting it in series with a signal generator and a scope. Stepping the generator's output in 10Hz steps showed a clear peak at 455.42kHz.

The frequency of these crystals is nominal and not exactly 455kHz. The IF has to be aligned to the crystal frequency rather than 455kHz. This also applies to other receivers with single crystal filters such as the RCA AR88 and National HRO.
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Old 11th Sep 2020, 12:58 pm   #55
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Default Re: Hallicrafters Skyrider Defiant SX24 Receiver

I do not have the SX-24 anymore, but I have now inherited the SX-25 (officially a basket case inside). I can look at the SX-25 for you and take pix, otherwise this is the infamous hand-drawn guide for the SX-25....

EDIT: and the voltage & restring guide for the SX-25 is included.
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