[Kenwood] TS-930: 2N5885 Power Supply Transistors

[Linden, Mike (BRC-Hes)]

  Thanks to all of those who replied on and/or off list to this query. Here
is a summary of the responses:

  The best way to guarantee equal current sharing between the two parallel
pass transistors (as in the 930's 28.5v final supply) is through the use of
emitter resistors on each pass transistor -- a matched pair of transistors
is not a solution. Without emitter resistors, one of the transistors is
probably going to wind-up carrying the majority of current leading to its
early demise (a common failure mode in the 930). Unfortunately, the Kenwood
930's power supply does not use emitter resistors on its pair of Motorola
2N5885 TO-3s.

  After discussing the details with Jerry, K0CQ, it looks like a pair of
0.100 ohm 10w resistors should address this problem in the 930's 28.5v power
supply. I have not implemented this change, but am giving it very serious
consideration.

  73, Michael N9BDF


-----Original Message-----

  I replaced the 2N5885s in my TS-930's high-current power supply a while
back. I'm now wondering if I should have used a matched pair since these
transistors are in parallel. Does anyone have any experience in this area
and know if I should have used a matched pair? And, if so, where I can get a
matched pair?