[Elecraft] Re: K2 mods

[Wayne Burdick]

"Bob Lewis (AA4PB)" wrote:
 
> Wayne, have you ever considered a diode (or even a Transorb) across
> the DC line after the fuse. It would have zero drop but if reverse
> connected, the fuse would open. With a transorb, it would even provide
> protection against over voltage.

Bob,

There already is a diode reverse clamp across the fuse: D12 (SB230). See sheet 1 of the RF
board schematic. A transorb would also work, but the diode is rugged, inexpensive, and
works very well. 

Between D10 (reverse polarity protection, now a super low-drop unit), F1 (self-resetting
fuse) and D12 (reverse clamp), the K2 is protected against almost anything that can happen
in the field, including accidentally reversing the internal battery. During tests we
reversed everything we could think of, and shorted the DC line to ground in several
places, and found that it was nearly impossible to damage the K2. The fuse limits reverse
current from a backwards internal battery to 100 mA or so, and it recovers when you remove power.

Compare this to the 20-watt radio from competitor "S". Their senior repair technician
admitted to me on the phone that if you reverse the power supply, about a dozen expensive
components will be taken out--most of them surface-mount.

73,
Wayne