Re the Zenith thing: I knew a guy who worked for Olympus cameras. The firm made lots of imaging devices, including medical ones. He told me the unofficial sales slogan for their proctoscope was: "Look up an old friend".
I really enjoy these kind of videos as well as those from TRX Lab and Mike's Radio Repair. Some great practical examples examples. Agree that it is much less stressful working on free gear that someone has given you :) I'm in the process of refurbishing my TS-830s which I purchased new in 1981. After moving to California and getting busy with other things it sat for close to 20 years. Now in a place where I can set up antennas without restriction and getting back into HF. The radio still worked OK for the most part, but needed some cleaning up and TLC after sitting for so long. Now that I have all the test equipment and a place to work on it, figured it was time to replace all the electrolytic caps, the finals and some related parts. Next up is addressing the band switches which have gotten a bit flakey, and then doing a complete realignment.
Nice repair ! I hate to say ( age wise ) I can remember the Zenith saying on their commercials in the early 60's when I was a kid messing around with old tube radio's . A day didn't go by without a mild electrical shock or a cloud of magic smoke being let out of some resistors in stress. Fun times .
Did you remember to solder the diode bypassed by a cap to the left transistor? This is part of the bias circuit. It turns down the bias if the transistor gets hot. It needs to be thermally connected to the transistor. Without this diode, there is probably no bias on the transistor and it is running class B. It will put out power in FM and CW and seem great but SSB and AM will be crap because the amp is not running linearly. Additionally, I would also add the blobs of solder to each of the legs of the transistors. This is used as another way to conduct heat out of the transistor through the legs.
@@IMSAIGuy Okay, right on thanks. Great video. Ironically, I have a IC-746 that just started showing the same symptoms after a power supply malfunction. I was able to follow your video and determine that the two transistors were causing my problem too.. you saved me so much time because all I had to do is open the cover and jump right to checking the voltage at the base of that transistor and sure enough... I was getting supply voltage at the base.,... way too high according to the schematics. Thank you so much. This radio was donated to me after losing everything I own in the big fire that destroyed Lytton, BC last year. I have only had the radio for two days now and then it stopped working on me... I am totally bummed out because radio is about all I have to do, being stuck in the side of this mountain.. thank you so much!
Well, I know it won't be the last (I'm at 4:25 now) because there's a part 8! But I'm wondering what caused it to fail. The radio worked fine when I boxed it away 20 years ago, and when I powered it up 6 months ago, it had low power out. Something failed that caused this cascade of failure.... Now I'm at @15:50! Congratulations .... but what is in part 8?
@@IMSAIGuy After seeing this video, I went and checked the voltage on the power supply I was using on it to make sure it wasn't putting out 24 volts or something! I've had power supplies fail to "overvoltage" and ruin equipment before I figured it out. (The PS was fine, putting out about 13 volts with or without load.)
This layout means that in a common emitter amplifier, the tab (emitter) is grounded. That in turn means you don't need to insulate the transistor from a grounded heatsink, and that means lower thermal resistance and no parasitic capacitance across the insulator. For these reasons, it's useful to have the emitter on the tab.
