HT-37 Choke Failure -- Why did this happen? What is your diagnosis?

Look, it has been 60 years, so I'm not looking for my money back or anything, but having just repaired the LV power supply choke on my very venerable Hallicrafters HT-37, I started thinking about how and why it failed. 

Clues: 

-- I found it with four of the windings broken, with the eight broken leads kind of sticking out of the winding wrap. 

-- The four broken leads were on the outside of the winding (thank God!) an were at the part of the winding closest to the chassis and the back of the cabinet.  (See picture below.) 

-- There was evidence of burning on at least two of the leads. 

-- The choke is located in the extreme back corner of the chassis, near the back of the cabinet. 

-- The paper and cellophane wrapping around the windings was a bit deteriorated.  

So,  what is your diagnosis?   What happened to cause the choke to go open? 

KC1FSZ's Peppermint III Homebrew BITX with Mods

Hi Guys:

I had some time over the holiday to finish off my second scratch-built rig.  I am very thankful that I got the work done on these projects before I read Pete's "Don't Build It" diatribe.  That would have been very demoralizing. :-)

Scratch build #2 (called Peppermint III) is still fundamentally BITX although I've made changes this time around.   I've switched to ADE-1 mixers with LO ports driven by adjustable gain buffers (ala N6QW LBS).  I've noticed that performance can be improved a lot if you can buffer/tweak the LO levels of the VFO and BFO (particularly carrier suppression on TX).  I did W7ZOI TIAs in the IF chain.  I've also taken the shielding/layout of the finals more seriously and have been able to dial up the power a lot (I did the KB1GMX thing with cutting off the drain pin on the IRF510 and using the tab).  The software is also greatly improved and now supports LSB/USB modes as well as software-driven PTT control for RTTY/FT8 and the hooks for my poor man's panadaptor.  I've been working lots of stations on QRO.

Total build time was about three months (half the time of #1) and the layout came out much smaller than before.  I made a trip over to Williams/Sonoma after Christmas and picked up the 2018 edition of the Peppermint Bark candy tin on discount and I think I can make it all fit.  More to follow ...

Happy New Year and 73s,

Bruce KC1FSZ

HT-37 FIXED -- Thanks for all the support

Don't worry-- I covered it with tape

This week I found myself with some unexpected free-time, courtesy of the government shutdown.   And of course, my thoughts turned to the HT-37.  I started thinking about the open choke in the power supply.  Four wires were sticking out of one side, four sticking out of the other.   Figuring out which went to which would have driven me nuts.   But it occurred to me that I could just wrap the four one on both sides together, and then just connect them with a piece of wire (see above).  I'd end up sacrificing three windings, but that shouldn't matter.  

It worked.   My AADE L/C meter won't measure up into the full Henry range, but  the choke was no longer open and the resistance looked right (about 230 ohms). 

I put it into the HT-37.   It works.  I had a long rag chew with AE2EE --  a guy who really knows his boatanchors.  He said it sounded great.  This contact was like icing on the cake.  TRGHS.  

Thanks to everyone who wrote in with offers of parts or suggestions on how to acquire a suitable replacement.  

Special thanks to Steve Murphy, N8NM who removed the LV choke from a junker HT-37and mailed it to me JUST AS I WAS LEARNING THAT THIS REPAIR WOULD WORK.  I feel bad about putting Steve to the trouble. I blame the shut-down.  Idle hands are the devil's workshop. And that broken HT-37 was bothering me. 

This was a very satisfying repair.  It was great fun to put the old rig back on the air.  And I did it without injuring myself.  Straight Key Night is right around the corner. 

Terminal strip for newer caps.  Repaired choke went to the two ends of the strip. 

W7RLF Homebrews a Receiver -- FB!

Ryan W7RLF has joined the small and elite group of radio amateurs who have homebrewed a receiver.  And it is a receiver filled with soul, juju and mojo; the project was inspired by Wes Hayward and Farhan, and used components from Hans Summers.   Congratulations Ryan and thanks for all the work you did in documenting your experience. 

Who will be the next intrepid ham to join the homebrew receiver club? 

Hello Sirs!

This month I read Wes Hayward's post on the history and heritage of DC receivers in ham radio and it brought a lingering interest to a head. I had to build one. I run the BITX40 and uBITX group on Facebook, and I posted to the other hams there: Which DC receiver should I build? Farhan recommended his DC40. Mind you, I've never homebrewed a radio before, so this is all new territory for me. 

I did build it, and it does work. It also uses QRP Labs stuff from our friend Hans Summers. This thing has a lot of QRP heritage :) I documented it every step of the way including all of my dumb moves and things I got wrong, and my desire is to inspire others to try homebrewing the way Wes, Farhan, Hans, and you YOU GUYS have inspired me to try it. I am hooked, of course! Here's a link to my blog to Part 1:

https://miscdotgeek.com/building-direct-conversion-receiver-part-1/

It's a four part series (unofficially 5 really) with 8000 words to it, and I hope you guys enjoy it and I'd be ticked pink if was worthy of mention on your show. Here's a video of it too:

https://www.youtube.com/watch?v=ju3kOEyCMYM

73 to you both and I wish you the best!

Ryan Flowers W7RLF

https://miscdotgeek.com

Ghost Ship: Oscar 11 Tumbles Through Space

First -- Happy Boxing Day to all our UK and Commonwealth friends. 

Oscar 11 is a UK-built amateur satellite launched in 1984.   It has been dead (well, almost dead) for many years.   But when the sun shines on the solar panels, it wakes up and transmits.   I've been able to hear it and -- more usefully -- see it on my RTL-SDR  HD-SDR receive system.  My antenna is my re-born (from the Dominican Republic) three element homebrew 2 meter cubical quad (see pictures below). 

I'm sorry the video is a bit out of focus, but you can clearly see the trace of the signal from the satellite. Realize that my HD-SDR software is about 10 kHz off calibration.  You can see the Doppler shift, and you can see the signal fading in and out as the old satellite tumbles through space.  Any ideas on what the other signals seen off to the side are?  Is anyone else listening for Oscar 11?  

https://amsat-uk.org/satellites/telemetry/uosat-2-oscar-11/

https://en.wikipedia.org/wiki/UoSAT-2

http://www.dk3wn.info/p/?cat=47

50th Anniversary of Apollo 8 (Great video!)

Indian Scientists Upbeat on Solar Cycle 25

https://earthsky.org/space/solar-cycle-24-25-sunspot-predictions