Monday, February 1, 2021

SB-401 Transmitter Rebuild Progress - Part 6 -

 In which I joyously announce all the switch contacts are cleaned!


 I have no idea why I took that picture, when the switch to the right of it shows a whole row of cleaned contacts to impress you with. Oh, well...

And all the rotary controls have been cleaned and lubricated, and more glaring examples of Poor Workmanship have been corrected.

And I started on the next item on the punch list, updating the AC Input connector. I removed the original connector, and penciled-in the cut-lines for the new one.

After I get the new connector installed, I'll start moving on to the Power Supplies in the radio. All new manufacture filter caps will be installed, followed by new rectifier diodes with higher ratings. The original diodes were rated 750 Volts PIV and 750mA Forward Current, while the replacements are rated at 1000 Volts PIV, and 3 Amps forward current. A bit overkill on the current ratings, but I have good supply of 1N5408 diodes from the little place back in Torrance I used to get items like that from.

And it's forecast to be sunny and in the low 60's tomorrow. Probably ought to get Sweet Little Wife's snow tires on. I think we're gonna have a slushy/snowy rest-of-the-winter.


12 comments:

  1. The part of my brain in charge of weird knowledge raised its hand and asked, "I wonder if Greenlee makes a punch for that shape?"
    According to their website, probably, but when I randomly checked on the prices for their special punches, they were way (stretch that out when you say it, waaaaaaaaaaaay) more expensive than I thought they would be.

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    1. The price is because we don't do much chassis punching anymore. But I think their prices back in the 50's and 60's were probably still not inexpensive.

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    2. And you may not always have the room to get a punch in there on a fully-built radio.

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    3. Last Greenlee punch I bought was for a DE-9 connector about 20some years ago, and IIRC it was about $75.

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  2. For Colorado piece of mind, two extra rims with studded tires is advised. This spring/summer shopping Craigslist can produce some great deals.

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    1. We have a set of 4 steel rims with studded snows on them.

      When she bought the snow tires, she went big.

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  3. GReat progress! And yes, you might want to change over! :-)

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    1. Thanks, NFO, but I figure I'm maybe 25% finished. If I keep at it, I'm hoping to have it finished in about two more weeks.

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  4. THe filter caps I can understand...But why replace the diodes if they aren't bad and will more than do the job? (Not that it hurts, but I fail to understand why).

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    1. I've seen the same question asked in the Heathkit forums. Some people say "If It Ain't Broke...", and "If They've Lasted This Long, They Should Be Good", and I generally agree with them.

      My view is that more modern diodes have much better surge characteristics, and if a diode is going to fail, it generally does it at turn-on, when the surge current to charge the new, higher capacitance, filters is greatest.

      The existing diodes are suitable, but I have the replacements, they're not very expensive, maybe $5 to replace all of them, and since I have to desolder them to correct some workmanship issues, I might as well replace them.

      It's a coin toss, but I'll feel better with the new ones in place.

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  5. I don't understand the tech but I like the pics! Well done!

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    Replies
    1. I'll be getting back to this tomorrow, after The Little Guy goes home.

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Keep it civil, please....