Building the filament PCB

Welcome back, everyone.

Today we’ll tackle building the third and final printed circuit board, the board which supplies current to the filament pins of the big 300 B tubes. This board has undergone some significant revisions in this “2014” version of the Kit 1 amp. The biggest change is the switch to these big, upright heat sinks. They are now mounted directly on the PCB, in contrast to the previous versions of the kit in which the heatsink was a single metal strip that made contact with the chassis. Here’s one of the groovy, new style heat sinks:

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This cute, little bugger is a regulator chip. It attaches to each of the heat sinks with a screw and nut. Its three long leads poke through holes in the PCB and then are soldered in from the underside of the board.

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Here’s the regulator chip in place and poking through the PCB:

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And here’s the underside of the PCB with the regulator chip solder joints:

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The soldering job above was the single most challenging task thus far in the building of this kit! It’s not hard to see why: those pins are very close together, and you need to be careful not to glob any solder where it shouldn’t be and short out the pins. If I’d had a pencil-point style soldering iron tip, it would have made the job much easier. In lieu of that, I found that melting a little solder on the iron tip and then touching it very carefully to the pin a few times served to get just the right, tiny amount of solder, enough to bond the pin to the trace on the board. Whew!

Now it’s time to solder in the two bridge rectifier chips. This is easy. The leads are very long and I trimmed them back after this picture was taken.

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Next we solder in some resistors…

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… followed by a bunch of electrolytic capacitors. Again, these are all polarized, so you have to be careful to get the positive and negative leads in the correct holes in the PCB.

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And, to our immense satisfaction and the rejoicing of audiophiles everywhere, the Filament PCB is done!

Next time, we’ll be doing a heap of wiring. Specifically, we’ll be inter-wiring between many different parts of the build – the 3 PCB’s especially – connecting all the amp’s innards in a harmonious manner.

See you soon!

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2 thoughts on “Building the filament PCB

  1. It could be the photography but the solder on the regulator pins looks clumpy and matte almost like the pins weren’t hot enough. Cool blog!

    Are you going to hire some unsuspecting soul to flip the switch for the first time while you watch from across the room? 🙂

    1. I think the soldering joints on those tiny pins are okay, but I’ll certainly check them out. What you’re observing may be an artifact of “iPhone photography.” As for flipping the switch, hopefully I’ll have performed all the recommended voltage checks before any switch flipping, thus minimizing the possibility of blowing up myself or my house! 😉

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