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Old 10th September 2013, 03:33 AM   #41
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Default Mounting power resistors

Brunk......can't tell from your pics, but.....

Power resistors can be very efficient BTU generators. When you mount them on a PCB, it's best to "stand them off" the surface of the board, so you can get airflow all around the resistor (and so the PCB and traces do not get damaged from the resistor's temperature).

I use a piece of a paint stirrer (thin pine board) placed between the resistor and the PCB to get a uniform spacing--and then slide out the piece of wood once the joint cools. (Yeah.... you don't have to use a spacer--but it makes the final product look more professional.)
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Old 10th September 2013, 03:37 AM   #42
brunk is offline brunk  United States
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Oh great tip, thanks!
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Old 10th September 2013, 04:03 AM   #43
brunk is offline brunk  United States
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Another question for you great folks!

In the BOM for the universal PSU, it calls for these particular heatsinks, but both Mouser and Digi-Key are backordered
http://www.mouser.com/ProductDetail/...OEL7Pxsw%3d%3d

would this be a suitable alternative in regards to dimensions and heat dissipation?
531302B02500G Aavid Thermalloy | Mouser

If not, can someone point me to an alternative that is available? Thanks in advance!

EDIT: Maybe this one would work?
http://www.mouser.com/ProductDetail/...rcyLuzrBrr8%3d

Last edited by brunk; 10th September 2013 at 04:26 AM.
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Old 10th September 2013, 06:09 AM   #44
brunk is offline brunk  United States
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I believe I have found an answer to my own question. I purchased some of these heatsinks
The dimensions are the same, with a couple holes for mounting options, and the heat dissipation is almost as good, along with a lower price

Last edited by brunk; 10th September 2013 at 06:22 AM.
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Old 10th September 2013, 08:02 AM   #45
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they only takes the smal TO-220 case diodes. and i don't like the 3 holes. the un-just holes will couse hotspots on the diodes.
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Old 2nd October 2013, 12:09 AM   #46
brunk is offline brunk  United States
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Hey fellas. Build is going great, almost finished stuffing all the boards! I have one question before i start to wire everything up though. The 5k variable resistors i ordered have 3 pins instead of 4 pins. Is this a big deal to have that 4th pin? I really can't find any info about it. Thanks in advance
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Old 2nd October 2013, 12:19 AM   #47
6L6 is offline 6L6  United States
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The 4 holes are there so you can use a pot with the pins all in a row, or use a pot with the center offset pin. You may use either kind.

There are no trimmers with 4 pins.
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Old 2nd October 2013, 01:08 AM   #48
brunk is offline brunk  United States
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Quote:
Originally Posted by 6L6 View Post
The 4 holes are there so you can use a pot with the pins all in a row, or use a pot with the center offset pin. You may use either kind.

There are no trimmers with 4 pins.
Thank you i appreciate it. I found another question for you guys lol. I googled the LED orientation in regards to +/- and found that the anode typically goes into the round hole i.e. "Short not square". However, the picture in the build guide shows the anode in the square hole. Is the picture correct?

Also, the Universal PSU LED has a schematic symbol of two semi-circle lines going through one hole, and the open side of the circle is on another hole. Is the hole with the 2 semi-circles going through it the negative?

Thanks again.
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Old 2nd October 2013, 01:17 AM   #49
6L6 is offline 6L6  United States
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The open part of the led marking on the pcb corresponds with the flat side of the LED.
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Old 2nd October 2013, 02:18 AM   #50
Hikari1 is online now Hikari1  United States
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Brunk:

"Zero" the pots before you solder them in. Put the pots to 0 ohms position (measured between legs 1-2 and leg 3). When you start it up it will be at 0 bias instead of potentially to high.
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