Newbie needs advice: F5 Build parts

[CanAm Man]

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.)

 

[brunk]

Oh great tip, thanks!

 

[brunk]

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...mX8fDDS2omdT3056KmDCfGDG6jpywhbE2wjOEL7Pxsw==

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...=sGAEpiMZZMttgyDkZ5WiutGzpRrwOi3frcyLuzrBrr8=

 

[brunk]

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

 

[AudioSan]

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.

 

[brunk]

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

 

[6L6]

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.

 

[brunk]

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.

 

[6L6]

The open part of the led marking on the pcb corresponds with the flat side of the LED.

 

[Hikari1]

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.

 

[AudioSan]

no need for that. the easy way is to measure resistance to 0ohm across the paralell resistors after it's all mounted.
then you don't have to consider if you need to measure 0ohm beetween leg 1 and 2 or between 2 and 3. that depends on wich way the pot is mounted. and the risk is that the pot is mounted the opposite way and then is adjusted to 5Kohm instead of 0ohm

 

[abadsantos 7]

no need for that. the easy way is to measure resistance to 0ohm across the paralell resistors after it's all mounted.

I strongly agree with Audiosan. Not just an easy way but it will ensure you are doing it correctly and avoid KABOOOOOMMMM....

Have read several advise turning clockwise until you feel the magic click click click...but there are several boards out there
which do not practically follow this rule. As Audiosan mentioned, mount it then measure the parallel resistor to measure at
0 ohm just dont forget to mark the direction though.

Doing this method will lesser your worries and will increase the chance of success upon start-up...

Regards...

 

[Russellc]

I just use a variac to fire up, no problems.

Russellc

 

[brunk]

I strongly agree with Audiosan. Not just an easy way but it will ensure you are doing it correctly and avoid KABOOOOOMMMM....

Have read several advise turning clockwise until you feel the magic click click click...but there are several boards out there
which do not practically follow this rule. As Audiosan mentioned, mount it then measure the parallel resistor to measure at
0 ohm just dont forget to mark the direction though.

Doing this method will lesser your worries and will increase the chance of success upon start-up...

Regards...

I just use a variac to fire up, no problems.

Russellc

Thanks to you both. I have done this prior to installing, and after to ensure 0ohms. I also bought a 5A variac for this reason too hehe. Don't want to call the Fire Dept!

Here is my work so far, still need to install the FETs. I'll be using this amp for headphones hehe
Link to pics on Head-Fi.

 

[Russellc]

Thanks to you both. I have done this prior to installing, and after to ensure 0ohms. I also bought a 5A variac for this reason too hehe. Don't want to call the Fire Dept!

Here is my work so far, still need to install the FETs. I'll be using this amp for headphones hehe
Link to pics on Head-Fi.

The variac made it easy. Just when bias begins to show, it is easy to determine with a slight turn which way does what. IIRC the F-5 biased at .59 or so, I worked them up to about .30 and let it cook a little while, then started to zero out the offset. Once that was done, (and it did take me a while to get a grasp on the back and forth between the two pots in doing this!) a little more back and forth to raise the bias and still maintain offset. HOPEFULLY Turbo F-5 will come up as well as original F-5 did. Good luck, you will love the amp.

Russellc

 

[brunk]

The variac made it easy. Just when bias begins to show, it is easy to determine with a slight turn which way does what. IIRC the F-5 biased at .59 or so, I worked them up to about .30 and let it cook a little while, then started to zero out the offset. Once that was done, (and it did take me a while to get a grasp on the back and forth between the two pots in doing this!) a little more back and forth to raise the bias and still maintain offset. HOPEFULLY Turbo F-5 will come up as well as original F-5 did. Good luck, you will love the amp.

Russellc

Thanks for the words of encouragement Russellc, I hope it goes safely and successfully for the both of us