Soldering the Preamp board

I said i was going to write up a bit more on this, and as I've already let the monkey fall from the sleeve (love that saying, my old economics teacher's literal translation of a dutch proverb, when he meant letting the cat out of the bag) there might be a slight lack of pictures. Mainly as I filmed the whole thing and forgot to take pictures.

Anyway...

So I was expecting the preamp board to be a bit more involved than the power, but really it's just a case of taking the printout of the scan i made of the board, and then firstly drawing on all the components as well as their numbers (ie R32,C43 etc) to denote whether resistor or capacitor. This took two attempts and a lot of head scratching (not due to nits I might add). First thing was wondering how the hell I'd ended up with a capacitor that seemingly didn't fit anywhere that seemed to be pretty integral to the operation of the depth control pot. Eventually with help from The Oracle (Tony, who's been helping me when I get stuck) it turned out that the PCB I had is for an original slo which didn't have a depth control.

Onto a bit of improvisation then, and the only place it seemed mountable was down the sde of the board, and it seemed a good idea to cable tie it. So I made a hole usng a screwdriver and a drill bit slowly drilling through the PCB by hand (it's not something you want a drill to break, slow and steady wins the race apparently, although I am sure this is a lie in any competetive sport). Anyway, that done I then spent the best part of at least an hour drawing on the components one by one and cross checking against the amp layout. Having a different PCB didn't help at this point, although it is close-ish to the amp layout I have. So a lot of time was spent figuring out where about 10% of the components should go and tracing tracks and double checking to make sure.

Wire bending tool

With the diagram done on a piece of paper I then went off and started soldering. This bit is pretty fun, and not really that hard. With a bit of care and due diligence and the amazing wire bending tool you end up with a nice clean result. Anyway the way I was advised by The Oracle to do this was to start with the smallest components by height, and then slowly build up. This means grab the things that when mounted will stick out the least and do them first, so when you flip the board to solder, they don't drop out. Anyway, as there are a few jumper wires on the board, I started with them (very important to mark them on your drawing, as they are easy to forget, and REALLY fiddly to do once there's a load of components on the board). Then I proceeded with the bridge rectifier (for the switching circuit). With this bit orientation is important, you want the AC (squiggly lines) orientated correctly so they are attached to the AC supply terminals. (That is unless you like things going bang and smoking lots. In which case there's a Youtube channel here that'll satisfy all your destructive desires: ElectroBOOM)

I then went and did all the resistors, moving from left to right for no particular reason other than probably that that's the way we get taught to read books in the western hemisphere. After which I sorted the capacitors into sizes from small to large and tackled them. At this point I should add, for the resistors it's a good idea to start at one end of the board and slowly move to the other side doing them in order of placement. Also, as you do each one, it's a good idea to tick it off on the drawing you have on the PCB so you know what you've done and can track anything missing. Capacitor wise it's a bit more chaotic as if you're doing it by size you'll be jumping all over the board, but hey, the end result clean board is worth it right?

With the capacitors one annoying thing was them being longer than the distance between the mounting holes on the PCB. So, one set of small pliers, I ended up bending the legs inward, fold over the edge, then outward again judging the required end distance between the pins by eye.You kind of want to end up with something like the image here which I've found as an example. It'll allow the cap to sit flush and the board to look clean, which is a good thing ad will satisfy your OCD when building. Also, clean electronics mean less of a headache later on when you invariably will need to troubleshoot something or much later down the line when you might need to replace a part (or add one when modding)

With all that done, just needed to add the depth capacitor to the side of the PCB and cable tie it into place resulting in the following wired PCB board (although it is missing the bias adjustment pot, the reason for this being that instead of being mounted internally it'll be mounted on the chassis as there's a nice convenient hole for it there meaning I won't have to pull the entire bloody chassis out to bias it like most amps require):


So there we have it, all the PCB wiring done. I'll still need to connect all the wires going from the PCB to the tube sockets and things like front and rear panel controls, FX loop etc, but the easy (ready non fiddly) bit of the wiring is done.

The next bit of wiring will be the heaters and lovely power valve and preamp valve socket stuff as that looks like a right time sink to do properly, but also like something that'll be pretty cool looking when done.

This is also a fun part to do. Seeing as there's loads of stuff that isn't fun, in future I'd probably leave this till after having done all the chassis work, transformer mounting and wiring of sockets as something of a pick me up. I'll know for next time.

Anyway, that's all for this post, the next one will most likely be on the hell of mounting transformers as that has not been fun ad is still ongoing..