[Elecraft] Re: KPA100 question

[G3VVT at aol.com]

In a message dated 23/04/05 11:55:05 GMT Daylight Time, johnmb at nc.rr.com  
writes:

It's  
always a good idea to leave a LITTLE air under power resistors, to help  
them dissipate some heat. Mine stood off the board about  1/8"


Reply: -----------------------------------------------
 
Can concur with that idea.
 
When I worked in TV repairs in the 1960s and PCBs first came into use,  we 
used to slip a small ceramic bead over the lead to give a  small stand off to 
prevent charring of the early laminated paper PCBs.  Failing this a small full 
loop in the lead was made around a jewellers  screwdriver to raise the heat 
generating component above the PCB, and also  provide mechanical support to the 
soldered joint. Anybody who worked on these  early PCB will be well aware of 
the effects that could occur. The  other problem apart from charring being when 
carbonised tracking between  the layers caused an internal break down between 
adjacent component leads due to  the higher tube voltages employed.
 
Latterly the method seems to be to "joggle" (kink) the component  lead to 
provide a mechanical stop against the PCB and assist in component  cooling where 
needed. The use of fiber glass PCB made the effect of heat  generation in the 
PCB less of a problem, though should still be avoided.
 
Bob, G3VVT