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Transistor Nightmare

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i63556

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Ok I got a dusey. I am rebuilding a 333 watt Dukane 1A833 power amplifier. This is a 1970's model. I am basically doing a cap replacement, changing the rectifiers, and the output transistors. This is a push-pull amplifier with '20' 2N3055 transistors for the final drive section. The 2N3055 transistors in the amplifier are of a 1970's vintage. Before rebuilding I am performing signal checks and the amplifier responds perfectly. When I replace the old 2N3055's with new beta matched 2N3055's the amplifier will not function. With the old transistors I can achieve a beautiful sine wave up to 75VAC. With the new transistors my output collapses at approximately 13VAC.

Are there differences between two different vintage 2N3055 transistors?

If so, what are they and how do I rectify the problem, thank you?
 

Optikon

New Member
i63556 said:
Ok I got a dusey. I am rebuilding a 333 watt Dukane 1A833 power amplifier. This is a 1970's model. I am basically doing a cap replacement, changing the rectifiers, and the output transistors. This is a push-pull amplifier with '20' 2N3055 transistors for the final drive section. The 2N3055 transistors in the amplifier are of a 1970's vintage. Before rebuilding I am performing signal checks and the amplifier responds perfectly. When I replace the old 2N3055's with new beta matched 2N3055's the amplifier will not function. With the old transistors I can achieve a beautiful sine wave up to 75VAC. With the new transistors my output collapses at approximately 13VAC.

Are there differences between two different vintage 2N3055 transistors?

If so, what are they and how do I rectify the problem, thank you?
Are the newer transistors destroyed after you take them back out?
Not knowing much else about your circuit, here is something to consider:
You _might_ be running the "new" 3055's into 2nd breakdown. What that would mean is that the SOA curve on the vintage ones is much wider than on the new ones. Take a look at your operating conditions and make sure you have sufficient margin in the SOA curve for the new 3055. I assume that the 20 parts are paralleled? Make sure there are current sharing resistors if you do this because if not, it is a one way ticket to second breakdown (hot spots forming and thermal runaway)
 

mozikluv

New Member
amp went kaput w/new transistors

:D hello there,

have you tried putting back the old trans coz you said it performed well before you made the replacement?

have you considered that one or a couple of your new transistors are defective? :)
 
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