Let's Fix a Blown Audio Output Transformer. 1937 Grunow Radio Part 4 [4K]

Last time, we found the reason this 1937 radio is silent - the audio output transformer winding reads an open circuit. Let's see if we can fix it! Time tags to jump around are in the first pinned comment.
This is Part 4 in this series on this 1937 Grunow Teledial Model 588. This radio was made around the time of the Hindenburg disaster.
Link to the series playlist on the 1937 Grunow: • Grunow Teledial 588
In Part 1 we carefully checked out the radio's power transformer to be sure it was not damaged, and then began carefully adding power through a current limited isolation power supply with additional fusing.
In Part 2, we reinstalled the tubes and began to power the radio up. We were able to get the same conditions reported by the previous owner when he plugged it in: some tubes lit, but there was no sound from the radio at all. We began zeroing in on the audio section after use of a signal tracer through the radio frequency stages of the radio.
In Part 3, we continue to troubleshooting and get into some focused testing of components: first we test the tubes; then the capacitors, and then plate voltages. Then we found "THE" problem: the audio output transformer.
In this Part 4, we inspect and test the audio output transformer. Then we attempt to fix it! Can we do it?
Along the way we use a vintage equipment tester, a Heathkit IG-72 Audio Generator.
Please review the safety information in Part 1. Tube type equipment has very high voltage and is dangerous. Take the time to research this for yourself. I mean this video for entertainment, not instruction; if you follow what I do, you are at your own risk.
References:
Excellent video discussing some basics of bench safety and power mains isolation by Mr Carlson's Lab:
• Tech Tips Tuesday, Iso...
Grunow and Grunow Teledial are brands of General Household Utilities Co., Designed and manufactured in Chicago, Ill. Closed 1938.
Vintage test equipment in this video:
Heathkit IG-72, ca early 1960's
Hindenburg disaster clip: public domain at archive.org
Camera: Canon G7X Mark III
Mic: Rode VideoMicro
Video Editing Software: Power Director

[@PracticallyFixed]

Jump to:
00:01 / Review of Part 3 - Discovering THE problem
01:46 / Removing the audio output transformer from the speaker basket
03:38 / Inspecting the audio output transformer
03:48 / Testing the secondary winding posts for resistance/continuity
04:00 / Checking the voice coil on the speaker
04:19 / Getting into the primary winding of the output transformer - observations
07:00 / More testing of the secondary winding posts - Hmm..?
08:14 / Getting into the secondary winding of the output transformer - uh oh!
09:23 / Speaker coil windings and the way the schematic is drawn - there's a humbucker...
10:41 / Working on repairing the winding on the output transformer
11:55 / Using epoxy to secure the leader wires for the primary winding
15:32 / Clarifying the schematic - the humbucker and how it is really wired vs the drawing
17:37 / Testing the repair with jumpers to the speaker - using the Heathkit IG-72 audio generator. It works!
19:06 / Preview of Part 5

[@KB4QAA]

Great demo. Too many are reluctant to dig into transformers. Thanks, 73. b.

[@PracticallyFixed]

Thanks! If you liked that one, here is one where I dig "a little deeper".
th-cam.com/video/q1DQVaXReX8/w-d-xo.html
Hope you enjoy that, it shows you don't need a lot fancy equipment but some old tools and some rusty junk certainly helps. Thanks again to you! 73

[@ericklassen742]

Nice repair. How lucky can one guy be? Btw, you can have that horseshoe removed surgically at any livery stable in the wikd west.

[@PracticallyFixed]

Howdy. Yep! Got lucky on this one. The horseshoe was embedded a bit deeper on the Emerson 641B radio repair video series Part 2 (th-cam.com/play/PLm_BfKDA0rpOk4ML1MQQnAjb_JJCDifpl.html&si=w8vemeBVVqgW83Pb). But the ol' farrier was able to dislodge the shoe with the the help of improper tools and a bunch of rusty junk. Check out the video entitled: "Audio Output Transformer Project, Save Me! - or - How I learned to Stop Worrying and Love Rebuilding Transformers". Was awarded extra points by "Fibber's Closet" for using a bait cast reel. Thank you for the kind comment.

[@jimburns348]

The way your shaking, I wouldn’t be handling anything sharp or pointy.

[@PracticallyFixed]

Hello Jim, and thanks for stopping by. I have enjoyed many of your videos, and your cabinet finish work is especially fine. Take care.