I have been looking at some of the hacks that require changing out values on the uBitx and bitx40 boards, and have a (hopefully simple question): what size and power value are the smd resistors?  I'm putting an order together for electronic components and want to make sure I get the right (same) physical size and the right power value.

thanks!

Sean 

All resistors are 1206's, 1/4 Watt.
So 0.12 inches long, 0.06 inches wide.
    http://www.resistorguide.com/resistor-sizes-and-packages/

Most look to be 1206 footprint.

Don't worry about power, the size sets the power.

We are lucky, they are the largest used mostly these days.  0805 will solder nicely in there too.

I buy from Mouser.  I have all values and probably 50 1% values.  I buy 100-500 at a time of a value.

On Mouser, hit the lowest price first button.  Lately I bought all my 1, 10, 100K values in 1%.

They were cheaper than 5%!

The more you see they have in stock, that is probably the best buy.

73's

Mike, WA6ISP

I have been looking at some of the hacks that require changing out values on the uBitx and bitx40 boards, and have a (hopefully simple question): what size and power value are the smd resistors?  I'm putting an order together for electronic components and want to make sure I get the right (same) physical size and the right power value.

thanks!

Sean 

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...

I assume most of that 1/4 Watt of heat max from a 1206 is assumed to be dumped into a PC board,
not dissipated into the air like a 1/4 Watt axial leaded resistor.
So best to derate to 1/8 Watt or so if hacking them in ugly style.

R141 on the Bitx40 is dissipating over 1/4 Watt, not a bad idea to replace it with something bigger
if it ever burns out on you.  Not many have reported this, but it does happen.
High ambient temps, high power supply voltages, and/or long key/PTT down times will do it.

Jerry, KE7ER

You can "Tombstone" 2 in series of 1/2 the value.

They stand up like an A formation. Tack solder at the top.  Gets them up in the air to dissipate.  Good way to double the power dissipation or use smaller sizes.

I hope 0603 stay popular, that is the smallest I can hand solder with my old eyes and shake.

I really like the fact that ASH used 1206's, they are big enough to hack easily.  They are going to become more expensive or go away as they get phased out for smaller parts.

73's Mike, WA6ISP

I assume most of that 1/4 Watt of heat max from a 1206 is assumed to be dumped into a PC board,
not dissipated into the air like a 1/4 Watt axial leaded resistor.
So best to derate to 1/8 Watt or so if hacking them in ugly style.

R141 on the Bitx40 is dissipating over 1/4 Watt, not a bad idea to replace it with something bigger
if it ever burns out on you.  Not many have reported this, but it does happen.
High ambient temps, high power supply voltages, and/or long key/PTT down times will do it.

Jerry, KE7ER

On Wed, Jan 17, 2018 at 08:35 am, Jerry Gaffke wrote:

All resistors are 1206's, 1/4 Watt.
So 0.12 inches long, 0.06 inches wide.
    http://www.resistorguide.com/resistor-sizes-and-packages/

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...

Normal use is with a good thermal connection to the pc board.
Hacked in they are often floating up in the air.
Perhaps the additional surface exposed to air will help enough to make up the difference,
but I doubt it.

Remember to de-rate a lot!

In Aerospace and Military we allowed 1/5th Rated power in resistors.

I would use 1/2 for our stuff at the max?

Take a 1W MOX power resister and run it at 1W.  Don't put your Finger on it!

Ouch!

Mike, WA6ISP

Normal use is with a good thermal connection to the pc board.
Hacked in they are often floating up in the air.
Perhaps the additional surface exposed to air will help enough to make up the difference,
but I doubt it.

On Wed, Jan 17, 2018 at 02:28 pm, Clark Martin wrote:

They should be capable of dissipating 1/4 W, They are designed to be attached to a PC Board.  It would make no sense to spec them for 1/4 W if they can’t handle that power in their normal use.

 

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...