Get Your 670 On - Power Supply
Whew. It has been a busy few weeks around here at the drip lab. I have been building like a crazy person, taking notes, and trying to absorb as much as I can so I can help y’all not have fear when it comes to building our products. I understand how daunting it can be to look at everything laid out in front of you, but like I have said before- if I can do this, you can too.
The first place to start for me, is the part of the build that is the most challenging. For the 670 build, that is the power supply.
I started with the 1 ¼ stand-offs. With these, you have an option of steel, or aluminum- this is strictly relative to the builder. Both do the job, well. The only difference is price, so for a budget build, my suggestion is to go with the aluminum. Just be gentle with these- I snapped a few heads off while tightening the kep nuts. That being said, the smartest thing to do is to order a few extra for times like that- I always say having extra left over is better than running out and having to wait for more to be shipped.
You will install three (3) across the top of the board, stand-offs facing down, kep nuts on the top of the board. The 1st, 5th, and 12th holes work best, but don’t be married to this placement- you will possibly move them when it comes to wiring the board depending on how you chose to place your terminal blocks for the main power transformer, power switch and IEC socket.
Next, install two (2) across the right side of the board, the 4th and 7th holes work best to complete the stand-off installation for the bottom of the board. Now, install the last two stand-offs on the left side of the board- the bottom corner is all you need for this side.
With this complete, you are ready to start populating your board. To me, this part feels like a fun, and semi-dangerous version of paint by numbers! Oooooh, danger! You can really start anywhere you want when it comes to populating your board- I chose to start with the tube sockets.
Quick side note before I go any further- It is imperative to keep your parts bagged up, in the bags they came in. Trying to figure out what is what, when you are in the midst of a build, is frustrating... Good talk, my friends.
For the tube sockets, you will need two (2) 8 pins, one (1) 9 pin, and one (1) 7 pin. Oh, tube sockets... they can get confusing if ya don't know what you are looking at. They aren't as confusing once you notice the dimple on the inner radius. which is also called the keyway by those that know the lingo. This dimple MUST line up with the line on the PCB. THIS IS IMPERATIVE. Sorry to yell, but the last thing I want is for you to not do this right, and fry your tubes when you fire up your 670.
Remember in an earlier post when I let you in on my little secret to keep these bad boys flat to the board, and not all cadywhompis for installation? Well, go ahead and tape those right into place. This tiny step saves you from spending too much time on one thing, using too much heat, and possibly harming your PCB with said heat. Be careful when placing tube sockets, when you fold the tab on the bottom of the board, if a track/trace is in close proximity and the pin covers/crosses it, it can short the board out. Once you have made sure none of the tabs are could short out the board, and the tape has insured that they lay flat against the board, flip the board over, and start soldering. I clean every solder joint when I complete it. This saves me time at the end of the build with cleaning.
Once you have soldered those into place, get your electrolytic caps together, and start populating. For these, use the 10k in the power supply, and 1k in the 12v and bias area of your board. All the caps are 450v, even if the UF changes. These babies are polarized, meaning if you put them in the wrong way... BOOM! The visual indicator for the polarization is the strip of negative symbols down the side of the cap, or the side with the short wire.
Once you have soldered those into place, you are ready to start placing resistors. The values are printed on the board for you, so this part is pretty simple. And this is where the paint by numbers analogy came into play. Put on some kick ass jams, and have fun with this... Only things you really have to pay attention to during this is that you need to use the 3w for the high voltage power supply, and pay CLOSE attention when populating the diodes. The graphic on the PCB matches the diode, so placement is easy, visually- except for the ones in the bias, those graphics are wrong on the PCB. Those four are flipped. If not placed properly, it will blow the diodes themselves, and capacitors like firecrackers... USE CAUTION.
Also, you will see a bunch of 909k spaces, and not have the resistors to populate those places- you needn't worry your pretty lil' head over those... they are for an external metering bridge which is not used for this application. The reason they exist is if you should chose to utilize an external voltage meter or for use with something like an Arduino. For this application, we have chosen to use trimmers instead of the 1k fixed, and 2k fixed. The reasoning behind this is by using the trimmers instead, you are able to fine tune the voltage exactly. The three (3) 50 ohm, and two (2) 100 ohm trimmers can be soldered to the board at this point. I like to use the tape trick on these as well so I can populate them all at once, and solder them all in one fail swoop.
For the next step, I chose to do the heat sinks. They come without the voltage regulators attached, so you will need to put the entire unit together. This is easy enough. To build these you will need: the volage regulator, the mounting kit, and the thermal pads. Place the thermal pad between the heat sink and the voltage regulator, put the regulator over the pad, and scew into place on the larger flat side of the heat sink. The placement ion the heat sink is important because if placed the other way, it will short out the pads of the voltage regulator. When placing on the board, you will need to gently fan out the pins so they slide easily into the footprint on the PCB. Here is a great place to utilize that taping trick I told you about... once you get one placed and taped, turn over the board and solder the pins from the voltage regulator. The fat pins from the heat sink are best left un-soldered- it is much easier to replace, fix, or do otherwise of not soldered. I soldered one of the pins on each heat sink simply because this unit is travelling across the pond and I didn't want them to have any wiggle room.
Now, we move on to fans. These babies need sixteen (16) stand-offs. 1/2 inch stand-offs work fine, but I prefer to use 1 1/2 inch ones because it allows for quite a bit of air flow over the board. Here, we used plastic ones. As with the other stand-offs, you can do aluminum- and for this application, the plastic are the better buy.
The fans need to be installed upside down, with the sticker on the bottom, and the sticker with the part number facing out. As you can see in the picture above, the wires all will be on the left side of the fan. These just require sixteen (16) 4-40 screws. Pull all the wires from each fan to the far left side, cut all the wires to one length, braid to the side, or zip tie to the side. twist and solder all the reds into one wire, do the same for the black.
Still have some unfinished business on your board? Well, go ahead and place the fuse lamps for the left and right channel heater, and the 12v. The bias is not fused, as it would be detrimental to the tubes if the bias suddenly shut down during operation. All that is left now is jumps, and the high voltage rectifier capacitor. Get on with your bad self, and place those suckas.
Whew. Do yourself a favor, and sit back, have a smoke and a beer, and pat yourself on the back. You have just completed the power supply!
I will be back with the next segment in the next few days. I hope you enjoyed this post, are excited about your build, and feel a void where fear once lived.