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Old 28th Feb 2021, 10:30 am   #1
ChristianFletcher
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Default Hallicrafters S20-R Sky Champion.

Hello everyone

I thought I would start a new thread about a Hallicrafters S20-R. I bought the set from EBay in December but haven’t had the opportunity to take a look until now. To say this set has been butchered would be an understatement. From a badly installed replacement transformer to shorting out capacitors and not to forget The 8 ohm speaker connected directly to the anode of the output valve. No output transformer. I thought I seen some awful radios in the past but this one takes the biscuit!

I have found some very good remastered manuals and diagram on the Bama boat anchor site but I’m looking for a layout of the underside of the chassis to locate components etc. I am also looking for anything with voltage measurement as I will have to rebuild the power supply section and this would be helpful. I don’t think this information exists unless anyone has made there own notes

If anyone could help provide information on this it would be greatly appreciated.

First questing does the band switch have a end stop position. The one I have rotates infinity but feels crunchy as it’s rotated through 360.

Thanks regards Chris
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Old 28th Feb 2021, 11:32 am   #2
HamishBoxer
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Default Re: Hallicrafters S20-R

I am certain the band switch does not go through 360 degrees, I will check as I believe I have this model. Typical , the set has gone AWOL but sure I am correct.
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Old 28th Feb 2021, 1:30 pm   #3
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Default Re: Hallicrafters S20-R

Thanks Hamish
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Old 28th Feb 2021, 1:38 pm   #4
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Default Re: Hallicrafters S20-R

I sympathise with your restoration quandary Chris but I hope you will persevere, the Sky King is a rather wonderful comms rx with its HF band that extends into low VHF. Hope you can get it ready for the next temporary licencing of the Alexandra Palace Channel 1 project
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Old 28th Feb 2021, 2:27 pm   #5
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Default Re: Hallicrafters S20-R

Does this help?

https://www.qsl.net/la5ki/s20r.htm

https://www.radiomuseum.org/r/hallic..._20r_s20r.html

It looks very similar to the SX24 model with the S meter replaced by an internal speaker.
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Old 28th Feb 2021, 2:42 pm   #6
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Default Re: Hallicrafters S20-R Sky Champion.

Have you tried looking in the VMARS documentation area?

Cheers
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Old 28th Feb 2021, 2:47 pm   #7
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Default Re: Hallicrafters S20-R Sky Champion.

Hello Chris

I've just checked the band switch on my S20R and it has only 4 positions, so it shouldn't go round 360 degrees. These sets are quite easy to work on, mine was a complete basket case. There's lots of info on the net.

Its quite common for the mains transformer and speaker to have been replaced. The original speaker used the field coil as the HT smoothing choke. Over the years they have usually failed, so it's common to see a separate smoothing choke fitted. Be prepared to replace all the paper smoothing caps.

Cheers

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Old 28th Feb 2021, 4:43 pm   #8
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Default Re: Hallicrafters S20-R Sky Champion.

Thanks for the Comments, I thought Vmars was just military radio equipment so no I didn’t think to look there. Thanks Andy for confirmation on the switch, makes me wonder why my one rotates. I can feel the ball indents I’m guessing there must be a damaged stop at one end. It does feel crunchy when rotating. Hello Graham the pictures were helpful thanks I was hoping to find something with some voltages for when I check out the power supply.

I will look up that SX24 model Thanks

I don’t mind replacement modern parts in a set but these one has been modified so badly it’s damaging.
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Old 28th Feb 2021, 4:51 pm   #9
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Default Re: Hallicrafters S20-R Sky Champion.

Resistance and voltage tables in here (pages 15 & 16):

https://bama.edebris.com/download/ha...emastered).pdf

Lawrence.

Last edited by ms660; 28th Feb 2021 at 4:55 pm. Reason: extra info
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Old 28th Feb 2021, 4:56 pm   #10
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Default Re: Hallicrafters S20-R Sky Champion.

Quote:
Originally Posted by AndyWright View Post
Hello Chris

I've just checked the band switch on my S20R and it has only 4 positions, so it shouldn't go round 360 degrees. These sets are quite easy to work on, mine was a complete basket case. There's lots of info on the net.

Its quite common for the mains transformer and speaker to have been replaced. The original speaker used the field coil as the HT smoothing choke. Over the years they have usually failed, so it's common to see a separate smoothing choke fitted. Be prepared to replace all the paper smoothing caps.

Cheers

AndyG4OJY
Turn the band selector switch past the normal travel probably caused damage to it, hopefully not too severe!
It's unusual that so many sets of that type had defective speakers.
I have a pristine example of a S20R. I have to check to see if it has the original speaker.
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Old 28th Feb 2021, 5:38 pm   #11
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Default Re: Hallicrafters S20-R Sky Champion.

Thanks Lawrence that perfect just what I need. For some reason I didnt spot that.

Thanks Dave I going to take a look at the switch now.

Chris
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Old 1st Mar 2021, 10:00 am   #12
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Default Re: Hallicrafters S20-R Sky Champion.

https://youtu.be/wBCo-_qiIm8

Ok the link above shows the radio playing something possible medium wave band given the amount of activity. I have substituted the output transformer for a signal tracer for now and was able to tune in stations on one band.

I have ordered one of the multi-tapped output transformer from RS components to try and match the 7000 ohm anode load for the 6F6. I think it may be a bit under powered for this set but it was cheaply a available so worth trying, not sure on the current rating etc. Probably should have checked that.

These sets appear to have quite a High B+ so not sure the mains transformer is up to the job but maybe a diode rectifier may help as the transformer doesnít have a separate winding for the rectifier.
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Old 1st Mar 2021, 3:40 pm   #13
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Default Re: Hallicrafters S20-R Sky Champion.

Quote:
Originally Posted by ms660 View Post
Resistance and voltage tables in here (pages 15 & 16):

https://bama.edebris.com/download/ha...emastered).pdf

Lawrence.
I can't understand why the manufacturer didn't include a voltage or resistance analysis in the service manual.
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Old 1st Mar 2021, 4:51 pm   #14
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Default Re: Hallicrafters S20-R

Quote:
Originally Posted by Julesomega View Post
I sympathise with your restoration quandary Chris but I hope you will persevere, the Sky King is a rather wonderful comms rx with its HF band that extends into low VHF. Hope you can get it ready for the next temporary licencing of the Alexandra Palace Channel 1 project
Looks like a great deal of bodgery and the cabinet is repainted, plus it has some of the wrong knobs.
I have an advantage, as a collector in the US, there used to be an unlimited supply of these US built sets, well care for and loved. I have to admit, I've been collecting for 50 years, so you tend to accumulate a few!
But then, I've only seen one Edystone receiver at a swap meet and the asking price was a little high, so I passed. It looked in good condition, as well.
Dave, USradcoll1.
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Old 1st Mar 2021, 8:16 pm   #15
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Default Re: Hallicrafters S20-R Sky Champion.

Thanks Dave as Lawrence pointed out the remastered manual does a have a voltage chart. The remastered manual is beautifully done must have been a lot of work. I often look at the radios available at relatively low cost compared to the U.K. I have imported a few radios from the USA and it’s often still cheap even with the high shipping cost.
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Old 1st Mar 2021, 9:52 pm   #16
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Default Re: Hallicrafters S20-R Sky Champion.

Quote:
Originally Posted by ChristianFletcher View Post
Thanks Dave as Lawrence pointed out the remastered manual does a have a voltage chart. The remastered manual is beautifully done must have been a lot of work. I often look at the radios available at relatively low cost compared to the U.K. I have imported a few radios from the USA and itís often still cheap even with the high shipping cost.
I looked up the manual and put in my documents folder. It is done up very well!
I have a real nice selection of receivers, but the shipping cost is generally a deal-breaker! Also all my receivers are for 120v/60cy mains.
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Old 2nd Mar 2021, 5:05 am   #17
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Default Re: Hallicrafters S20-R Sky Champion.

http://www.nostalgiaair.org/pagesbym...3/M0008893.pdf

Is a schematic, but no pictorial. Sam's does not have it listed , nor does Beitmans Most Often Needed Radio Diagrams.
I typed into Google: Bottom of chassis picture hallicrafters 20r and turned up a lot of pix under the chassis, some blurry, some fairly good. HTH.
I did have one of those decades back. I will try to get to the schematic cabinet for hallicrafters & see if I still have an OEM manual for it, that I can copy & send you.
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Old 2nd Mar 2021, 5:04 pm   #18
usradcoll1
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Default Re: Hallicrafters S20-R Sky Champion.

Quote:
Originally Posted by FrankB View Post
http://www.nostalgiaair.org/pagesbym...3/M0008893.pdf

Is a schematic, but no pictorial. Sam's does not have it listed , nor does Beitmans Most Often Needed Radio Diagrams.
I typed into Google: Bottom of chassis picture hallicrafters 20r and turned up a lot of pix under the chassis, some blurry, some fairly good. HTH.
I did have one of those decades back. I will try to get to the schematic cabinet for hallicrafters & see if I still have an OEM manual for it, that I can copy & send you.
Sams covered models built in 1946 and newer. Beitmans covered earlier models, but didn't cover every model, made by the manufacturer.
The early Sams Photofacts were reprints of the OEM manuals like Riders and Beitmans, where the newer Sams were totally researched and redrawn.
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Old 8th Mar 2021, 6:17 pm   #19
ChristianFletcher
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Default Re: Hallicrafters S20-R Sky Champion.

I was working on the S20-R this weekend and I now have the radio making itís own sound. I have installed a mult-tapped output transformer from RS components and this has matched well with the speaker and the radio sounds ok for me. The electrical specifications for the transformer list primarily current as 40ma and I am measuring 35mA of current through the transformer. The data sheet doesnít specify if the primary current is a nominal value or a maximum. Would it be worth increasing the valve of the cathode bypass resistor to further reduce the current

I have also replaced much of the damaged power supply wiring and sorted the shorting local oscillator tuning gang problem.

I donít the the AVC is operating correctly at the moment as the set appears to be overloading but the rf gain control does the trick when the AVC is switched off. Also have no BFO at the moment and was going to tackle those next.

More good news is that the band select switch does work on all bands even though it feels rough. I did a quick check on each band it works but big variation in sensitivity

Anyone interested can see the work going on here https://youtu.be/eGspnbj2PE8

Thanks regards Chris
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Old 12th Mar 2021, 11:46 am   #20
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Default Re: Hallicrafters S20-R Sky Champion.

Fixed the problem with the mains hum by adding a little capacitance to the screen grid of the RF amplifier. It’s not clear if the original capacitor is fitted as it’s buried at the back of the coil box but I can see a hack job going on in that area. Adding 1uF silenced the hum so I actually reduce the value to 680nf as I like a little hum as a telltale it’s switched on.

I’m after some information on the BFO coil if anyone is in a position to take some measurement for me. Thanks
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