Zenith Troubleshooting Challenge - Transistor Clock Radio Repair Mid 1960s Model B258W [4K]

Let's take a look at this 60 year old transistor clock radio. It appears to be from about 1964 but I am not certain of its date. The chassis was used in many models with differing case designs and consists of only 4 transistors. It can run quite well being driven by a single output transistor as a Class A amplifier.
Unfortunately, this little clock radio does not work. Let's see if we can bring it back to life using some troubleshooting logic - but with a dose of luck.
See the checklist which appears when status changes, for tracking what is discovered that needs addressing in Red, followed by Green when resolved.
NOTE: This is not instruction, it is for entertainment for people like me who enjoy watching projects and the experiences gained. If you attempt to do any of the things in this video you are at your own risk. I am using special tech-bench safety equipment not detailed here so don't take for granted you can just plug these old items in safely without them being checked and repaired correctly. Check out the link below to Mr Carlson's Lab video below.
ACKNOWLEDGEMENTS AND REFERENCES:
[note: am in no way representing how these folks have shown doing these things - I don't even think they would approve.]
Thanks again to Tony at xraytonyb for a great way to attach an inexpensive frequency counter to a signal generator and power it from the generator as well. • Tenma Signal Generator...
‪@xraytonyb‬
Thanks to shango066 for championing the approach of "fix it first", before mass re-capping. See shango066 for many examples of that approach.
@shango066
Awesome discussion of bench safety including variacs and isolation transformers by Mr Carlson's Lab (highly recommended):
• Tech Tips Tuesday, Iso...
‪@MrCarlsonsLab‬
Modification method for a commercial Tripp Lite isolation transformer for tech-bench use by Todd Harrison, his channel is called ToddFun:
• ToddFun.com: Isolation...
‪@ToddFun‬
People who may enjoy this video will interested in: portable transistor radio, Zenith transistor radio, 1960s radio, radio repair, radio troubleshooting, capacitor wizard meter, old radios, AM radios, clock radios
Camera: Canon G7X Mark III
Mic: Rode Micro
Video Editing Software: Power Director
Video Editor: just me

[@Simon-mz7sf]

Nice work on engineering stability to the different IF transistor characteristics. Enjoyed watching

[@terryblackman6217]

Very enjoyable video. I am glad that you showed the alignment. So many people skip this in there videos, but for a beginner it's an essential part of the restoration. Nice one.

[@PracticallyFixed]

Glad you enjoyed it. Thanks for the comment.

[@hestheMaster]

Great repair and clean up. It looks and sounds good for it's age. My grandmother had one like it but the clock froze. That
was back in the early 1980's . They did like their Zenith's.

[@PracticallyFixed]

Thanks Steve.

[@DERB_Seymour_Indiana]

Good solid troubleshooting PF. Nice showing the fault both ways on that IF transistor. . Those dome top transistors are known to be unreliable and often bad. My first thought was the GP transistor had different characteristics when you lost signal at normal voltage. Those GP transistors are often good for testing but once the problem is confirmed it's best to find a closer match. Of course your method of the repair being temporary unless it works is also acceptable. LOL Good little performer for what it is. :)

[@jimnewman5596]

Great troubleshooting video. The substitution transistor works very well, and it is interesting that the pF capacitor fixed the issue you were having.

[@PracticallyFixed]

Thanks Jim. Oscillation feeding back through the AVC is my guess of what was happening. Interesting way to find the solution, the VOM lead. Thanks again.

[@ianallen2]

A very nice clock radio. It fought you a bit but you won.

[@jimburns348]

Nice sleuthing there Holmes.

[@PracticallyFixed]

Thanks Jim. Enjoy your videos.

[@Godunjoify]

Nice TroubleShooting. I liked it.
But i dont understand how a higher voltage is the cause for the Oscillation?

[@PracticallyFixed]

Thanks. Yes, I agree; wish I could explain it. I was beginning to work on understanding what was going on with the bias voltages when discovering the capacitance would make it work.