Tuesday, January 12, 2021

SB-301 Rebuild Progress - Part 4 -

 So, I spent some time making sure all the dial tracking issues were solved, and then put the front panel back on the radio, taking care to align the panel as specified in the manual, as if you don't do it correctly, the dial can bind up, and things can wear out. Then I cleaned the knobs and dial bezel, polished them a bit with some "NOVUS #1" cleaner/polish, and reinstalled them.

Then I flipped the chassis over, and began inspecting all the soldered connections, and checking for "Workmanship Issues" like unclipped wires hanging through terminals, like this one on the center terminal.

And this poorly terminated coaxial cable. The ground braid goes to the third terminal from the right, and you can see all the individual strands. The soldering on the capacitor on the right end of the terminal strip wasn't too neat, so I re-did those, too.

And you can see some excess lead length through the terminals on this wafer of the VHF Converter Select switch. This, too, was corrected.

In all cases, the solder was wicked off the connection using "Solder Wick", the excess lead was wrapped around the terminal like it should have been when first assembled, and then resoldered. This is more a reliability issue than a functional one, as the connections were soldered acceptable well, but "Accepted Practice" states you wrap the lead around the terminal to make a solid mechanical connection, and then solder it. Solder has very little strength; it's just there to enhance the conductivity of the mechanical connection, and to "seal" the joint a bit. Oh, sure, we've all just "tacked" connections together to bypass a bad part, but if the assembly that tack joint is in gets  subjected to vibration or rough handling, it might very well fail and pop loose. If the device just sits on a desk it's entire life it might work for 25 years, but it's not the right way to build things.

Tomorrow's activity will be to start the process of changing the 120VAC Input Connector from an old "Two Pin" style, to a modern three pin style that uses a three-wire line cord to ground the chassis of the radio.

This will require some metal work, as the mounting holes are further apart on the new connector, and the hole for it is wider and taller. The positioning of the new connector will be such that the lettering "120 VAC" will remain, but the "INPUT" label will be gone. Small price to pay to have an easily replaceable power cord, as the two-pin style cords are now considered "Vintage" or "Antique", and the prices have shot up.

I'm also going to change out the antenna connector, from an "RCA Phono" style to a BNC female. 

I did the "Initial Tests" in the manual tonight, confirming I didn't make any mistakes rewiring the power supply. After I change out the power connector, I'll be ready to begin the alignment procedure.




Keep it civil, please....