Looking for SS parts

J D Sauser · Post by **J D Sauser** » 13 Apr 2000 2:11 pm

Just spent 3 hours on that #&%^# www... and it would seem that I NEVER find what I'm looking for.
I just got a Sho~Bud amp in and it would that the previous owners have monkeyed around in it... and replaced some transistors with what ever they thought looked "cool".

Anyway, it looks like NOS tubes are much easier to find than old transistors(?).

In this case I am looking for RCA 40636 transistors.
ANYONE have a source for old SS parts?

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jaydee@bellsouth.net

Mark Amundson · Post by **Mark Amundson** » 13 Apr 2000 2:41 pm

Those old 40XXX parts from RCA will likely be cross-referenced to NTE equivalent or some similar semiconductor line.

After having blindly following the cross-reference books for years, I took advantage of my EE education and do my own matching based on the old specs and look for a "present day" matching equivalent from a more common set of parts. You'd be surprised how thousands of old parts are replaced by a single new part with better performance as the result. I'll check into your part number and see if I can find a sub.

Mark Amundson · Post by **Mark Amundson** » 13 Apr 2000 2:58 pm

Your 40636 part is TO-3 can (flanged) NPN Power Transistor with a 15 ampere collector current and Vceo of 80 volts or more. The direct replacement is a Motorola 2N5878, but a Motorola 2N5882 is a present day recommended part for best availbility and lowest cost (probably a few bucks each at retail).

A modern MJ15015 will also work, but its a little overkill on the Vceo rating (120v).

J D Sauser · Post by **J D Sauser** » 14 Apr 2000 4:43 am

Thank you very much Mark.
I'm no good at electronics, so may I ask;
Which one is the best, in quality for a power amp application?
Where do I buy these?

Thanks a bunch!

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jaydee@bellsouth.net

Mark Amundson · Post by **Mark Amundson** » 14 Apr 2000 6:25 am

Mouser Electronics (mouser.com) sells the 2N5882 for $2.02 and the 2N5878 for $1.42. Both are nearly equal for the audio power application, but you may want to choose the 2N5882 part only because Motorola promises to continue to build replacements for awhile longer.

Mouser does not sell the Motorola brand, but the other suppliers are good too. Since the price is fairly low, consider replacing all the 40636's with 2N5882's for best current sharing.

J D Sauser · Post by **J D Sauser** » 14 Apr 2000 7:15 am

Thank you very much!
Right now there are two 2N3773 in it. The amp works great, but I want to be sure there's nothing in there that could cause damage and as they did not seem to be the original ones I've got in my other Sho~Bud...
... J-D<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by J D Sauser on 14 April 2000 at 08:23 AM.]</p></FONT>

Mark Amundson · Post by **Mark Amundson** » 14 Apr 2000 8:36 am

The 2N3773 is 16 amp (Ic), 140 (Vbe) NPN power transistor commonly used in 1970's through 1980's high power audio amps. I know Peavey and Crown International used alot of these types then. Motorola still makes the 2N3773 as a standard part. They are overkill for the RCA 40636 application (15A, 80V), and the beta (current amplication) of the 2N3773 is a tad lower than the 40636/2N5882 types. But the 2N3773 is close enough of a fit, that a service shop probably had them in stock, and used them instead of ordering other types. $2.96 at Mouser for the 2N3773.

Beware, if you are not used to replacing TO-3 style transistors, have a technician do it for you. There is some skill needed to prevent shorts to chassis/heatsink and buttering the right amount of heatsink compound on the mica insulator and transistor bottom.