On Wed, 28 Dec 2011 14:20:26 -0000, "froggiegremlin"
Hello all: Just got a blown TM503, the MOT power transistors on the heatsink in the back power supply, are blown. Manual has =I looked into this a couple of months ago and concluded that the BD809
(NPN), BD820 (PNP), MJE2955T (PNP), MJE3055T (NPN), TIP33C (NPN), and
TIP34C (PNP) would be readily available acceptable substitutes in
roughly that order.
Just be careful of the pinouts. The Tektronix TO-127 parts are ECB
while the TO-220AB and TO-247 parts listed above are BCE. I have not
done a serious search for a modern high power part with the same
pinout or TO-3 parts (for high power compartments?).
The 2N5191 (NPN) 2N5194 (PNP) or 2N5192 (NPN) 2N5195 (PNP) are lower
power, 40 watts instead of 90 watts, but might work in non-power
supply compartments and have the same ECB pinout in a TO-225AA
package. The BD439 (NPN) BD440 (PNP) or BD441 (NPN) BD442 (PNP) are
similar with an ECB pinout in a TO-126 package but 36 watts. I
suppose you could parallel them with emitter ballast resistors but
that is just as much work as dealing with the wrong pinout nevermind
the mounting considerations.
What is the selection for the NPN MJE2801?As far as I know, the 151-0349-00 is the raw stock number and the -05
version was selected after a 72 hour burn in. If they selected for
anything, I imagine it was a minimum current gain of 25 hfe at 3 amps.