HAMPTONe3. HVTP2 POWER SUPPLY ASSEMBLY.
Or NEXT STEP
OVERVIEW: The HVTP2 power supply board consists of two regulators designed to deliver 20mA @ 200VDC and 200mA @50.4VDC. The +50.4VDC powers the 4 tube filaments (all run in series), and is used for phantom power. Though the supply is running at a less than ½ its full rated power, it is only guaranteed to work at the load current designed. The circuits are optimized for minimal power dissipation for the HVTP2 kit, and are not guaranteed to work properly for other circuits, or under more load current. Both regulators are designed to soft start, meaning the voltage ramps up over several seconds instead of instantaneously. Both regulator circuits have two stages, a Mosfet pre-regulator, followed by a linear regulator, and are in many ways near identical. The Mosfet pre-regulator protects the linear regulator from ever seeing too much voltage across it (35vdc differential max input-output, mostly during power up) and provides a very clean input to the regulator. The cleaner the power going into any linear regulator, the cleaner it will be coming out. In addition to the very low noise output of the +50.4vdc circuit, each channel has an independent two stage RC low pass filter, to further reduce any possible noise and power on pop; resulting in very quiet phantom power.
The procedure will be very similar to the channel card assembly in that you will start with the low profile parts, and work up to the taller ones. For test reasons, DO NOT install the bridge rectifiers until instructed. Leaving one out will allow you to power up the +50.4VDC first, then the +200VDC.
1. Install the ½, ¼ watt resistors, and diodes just like you did on the channel card, keeping them snug against the board (do not install the larger power resistors until step3). Resistors do not have polarity, the diodes do. They must be installed with the proper orientation (see the "Component ID page on the tech support page of our website if you are unfamiliar with the different types of parts). D35 and D51 are zener diodes. They generally look orange/brown with a black band indicating the negative end, whereas the regular rectifier diodes (1N4007) are black with a white/silver band indicating the negative end. It is extremely important not to mix these up, and to have the polarity correct.
2. Install the two 0.047uF caps C34 and C53, and the trimpots R39 and R54. R39 is a 200 ohm pot, and will have the number "201" marked on the side. This means "20" and 1 zero = 20 + 0 =200. R54 is a 1k pot with the number "102" on the side. Again this is translated as "10" + 00 = 1000.
3. Install the power resistors R34, R36, R50, R52, and R55. For these parts, leave a 3/8" to 1/2" gap under the part. This provides better airflow, and mechanical relief.
4. Install U52, the LM329 voltage reference. It is a TO92 package and looks like a small transistor.
5. Attach the two smaller silver heatsinks HS31 and HS51, to the voltage regulators U33 and U51 (the 2 x LM317). Make certain the regulators are all the way into the heatsink. Install them into the board and solder in place. You may find the tabs on the heatsinks barely comes through the holes, and are a bit difficult to solder. The trick is to put the tip of your iron into the hole and heat the heatsink, once it is hot it will conduct solder down into the hole. The tab is only for strain relief and does not connect the part electrically, so if you have trouble with this, they don’t have to be soldered. The reason they are a bit short is because I am using the LM317 "F" version of the regulator, which has an isolated plastic tab (normally the metal tab on a TO220 package is connected to the middle pin of the device). The package of these is a little taller than the standard TO220, thus the mounting tab ends up a little short. If the standard package were used, the output voltage of the regulators would be on the metal heatsinks (in this case +50.4 and +200vdc) making it somewhat dangerous, and easy to short out. The tradeoff was made to have the regulators be safely isolated, at the expense of the heatsink being a bit tricky to install.
6. Attach the large gold heatsinks HS30 and HS50 to U31 and U50 (2 x IRF820 N channel mosfets) using the following hardware (in this order): 5/16" panhead 4-40 machine screw, into the black shoulder washer (shoulder facing away from the head of the bolt), through the Mosfet with the shoulder going into the mosfets hole, mica insulator behind the mosfet, put this through the middle hole in the heatsink, finally attached the 4-40 lock nuts on the backside of the heatsink. Thread the lock nuts on so they are snug, but not tight, and making sure the shoulder washer is properly seated inside the IRF820s.
7. Install the large heatsinks into the board. Solder the two large pins on the heatsink to the board, making certain the heatsinks are snug against the board. Depending on your iron, it might take a few seconds to heat the pins enough to get the solder to flow. Place your iron on top of the pin, and begin to flow solder onto it. Hold the ball of molten solder on top until it starts to flow down on its own. The pcb board will heat very quickly, so you don’t need to heat it much, focusing the heat of the iron to the pin on the heatsink. Generally when soldering, you are trying to get the two metals to both be hot enough for the solder to flow between them. If the pins aren’t hot enough, the solder won’t take. Allow the heatsink to cool, then tighten the mounting hardware for the Mosfet. Finally solder the mosfet and cut its leads. With an ohmmeter, make certain there is no continuity between the center pin of either IRF820 mosfet, and its heatsink. The point of the shoulder washer and mica insulator is to electrically disconnect the tab from the heatsink, reducing the risk of damage and/or serious death to you or the supply.
8. Install the rectifier B30 in place, this powers the +50.4vdc regulator. The "+" mark on the rectifier goes into the square pad on the board.
9. ADD PICTURE Install all the tall electrolytic caps except C50, the 220uF 400V cap, following the same method you used for the audio channels. At this point everything except B50, C50 and the point to point wire should be installed. Leaving C50 out makes wiring the transformer to the board much easier. Make certain all the negative sides of the caps go to ground, and the + terminal on the rectifier is into the square pad (negative end to ground). Double check the polarity of all diodes, and make certain you didn’t mix up the zener diodes with the regulator ones.
10. Perform a visual inspection of all solder joints, and reheat/re-flow any that don’t look right. Make certain there are no solder bridges shorting traces together.
11. Clean the board in the same way you did the audio channels, to ensure there is no flux residue on the board.