Any idea to replace transstors on an Altec 9440A power amp

How many years may the transistors (6 pcs 2N3584 and 16pcs 2N6259) last.

Can one expect problem after +35 years ?

Any recommendation to replace these due to age ? Will these detoriate with age ?

Are these still available ?

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How many years may the transistors (6 pcs 2N3584 and 16pcs 2N6259) last.

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There are entirely too many variables for this to be specified.

Under normal operation where they're operated comfortably within their limits they should last indefinitely.

Conditions such as excessive thermal cycling, over-driven inputs, and improperly loaded outputs, as well as other internal component failures can serve to dramatically shorten the lives of output transistors.

Age alone should not be a cause for concern. It's generally not a matter of course to replace healthy output devices. But, i'm sure there are exceptions where better versions of the originals have been developed which may impart an improvement in an amplifier's sound. I think this is somewhat subjective and variable among specific designs and original components.

If one had the opportunity during a thorough refurbishment it is probably advisable to test the outputs for general health and leakage on a quality transistor tester to ensure that pairs are still reasonably well matched.

Just my .02...............

As the amplifier now in part I would like to do a complete check.

How to check / locate faulty transistors?

A) Acc. to the manual a low power ohm meter could be used. Open circuit voltage should be less than 0,6 VDC, when testing groups of transistors at plug P2.
When a defective indication is found for a group remove the transistors one at each time for individual check.

B) Acc.to the manual an optional is a PN junction insensitive continuity checker.

I am not sure how to perform either A) how to use an ohmmeter or B) how to to use a PN junction tester.