Topband: FairRite Products 2873000202

[Andy Ikin]

"I have been using no.27 enamel wire with only the secondary within a teflon tube in the core. 
The primary is wound around the telfon but clearly touches the bare core -- are you saying this is not good?  Pete W2PM"

Pete, I hadn't bargained for such response to my posting; 

However, Tom's posting puts the issue into a correct prospective

"You should avoid scratching through the enamel, especially
if the core contacts another conductor.
Normally enamel is not a problem, but at times if a single
layer of enamel is used it can be scratched through.
Actually you don't want to scratch the wire with ANY core.
The reason is pretty obvious, that bare spot might touch
another bare spot in a winding (which is worse than core
contact). Changing to 43 material does not totally solve the
problem."

My experience is based on the use of these cores in receiving antenna applications ( low noise transformer feedback amplifiers ), over the past 9 years I have wound thousands of transformers using two hole type 43 material cores and to my knowledge no failures have been attributed to either shorted turns or wires touching the core. However, I have recently noticed that some Fair-rite cores ( made in Red China ) have a rough surface compared to US manufacture, I have yet to determine whether this may be problem!!!

73s

Andy  Ikin G8LUG