The SJ numbers were house numbers. 7739 is the date code, that part was made in the 39th week of 1977. What power supply?
Do you have a schematic? If it is a basic pass transistor in a regulated supply, then it really isn't critical. Get something of same polarity - NPN or PNP - of sufficient voltage and current rating, and off you go. Back in that era the 2N3055 was VERY common as a high power (for then) transistor. Today I usually reach for an MJ15003 or even an MJ15024, unless there is a compelling reason not to. The compelling reasons are usually a matter of stability in a power amp. That is not likely to matter in a power supply.
SJ numbers were assigned to the OEM purchasing the part. As such it is proprietary information. You could call On Semi (Motorola) and ask if they can tell you anything about the part, but be prepared to hear that it is proprietary.
Do you have a schematic? If it is a basic pass transistor in a regulated supply, then it really isn't critical. Get something of same polarity - NPN or PNP - of sufficient voltage and current rating, and off you go. Back in that era the 2N3055 was VERY common as a high power (for then) transistor. Today I usually reach for an MJ15003 or even an MJ15024, unless there is a compelling reason not to. The compelling reasons are usually a matter of stability in a power amp. That is not likely to matter in a power supply.
SJ numbers were assigned to the OEM purchasing the part. As such it is proprietary information. You could call On Semi (Motorola) and ask if they can tell you anything about the part, but be prepared to hear that it is proprietary.
For an even simpler answer: what are the actual needs?
As in: "it regulates down from raw18V to regulated 14V and load consumption is 3A" or whatever.
Then rather than "a substitute" we can suggest what modern part fits the job.
We already know it's TO3 metallic and yes, it *might* be a 2N3055 unless we are talking some hairy specs
PS: *confirm* it's actually an NPN part, they might as well have used a PNP one.
As of the "small ones" , are they bad or something?
Why do you want to replace them?
I hope you are not trying to "repair" that supply buy shotgunning parts.
In fact, what's the problem with the TO3 transistor currently there?
As in: "it regulates down from raw18V to regulated 14V and load consumption is 3A" or whatever.
Then rather than "a substitute" we can suggest what modern part fits the job.
We already know it's TO3 metallic and yes, it *might* be a 2N3055 unless we are talking some hairy specs
PS: *confirm* it's actually an NPN part, they might as well have used a PNP one.
As of the "small ones" , are they bad or something?
Why do you want to replace them?
I hope you are not trying to "repair" that supply buy shotgunning parts.
In fact, what's the problem with the TO3 transistor currently there?
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