PA400 questions

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roebas
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Joined: Mon Jul 03, 2017 5:51 am

PA400 questions

Post by roebas » Mon Jul 03, 2017 6:02 am

Hello, I recently got a defect old Peavey PA400 5A amplifier from a friend. I noticed that there was done already a lot of bad repair work to this amp earlier. One of the SPS761 was replaced by an BC556 which is not a compatible replacement type.
After replacing the two SPS761 by two 2n5401 transistors the amp worked again. But by checking everything I have the following question.
Is it normal that there is no quiescent current running throught transistor TR10-TR-15 (see pdf)?
Any help would be much appreciated.

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Kind regards,
Roeland

Francis Selim
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Re: PA400 questions

Post by Francis Selim » Mon Jul 10, 2017 7:16 am

I once repaired two of these very nice amplifiers but i had a problem obtaining the transistors 60142s and later on just used 2N3772. i couldnt get the high quality 2Ns though then I got 2N3773 but also overheated on being pushed hard.

The transistors you refered to Tr10-15 actually should conduct when the signal level is high enough for Tr 8 and 9 to switch them on. They are only to output the required amplified signal. I did not replace the 761 with Bc 556, Peavey can help you to get the replacement cross-reference. they gave me for the 60142s. Good luck

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Enzo
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Location: Lansing, Michigan

Re: PA400 questions

Post by Enzo » Mon Jul 10, 2017 5:19 pm

Today I would load it with MJ15003 and forget the 2N types.

I don't expect more than a few milliamps at idle.

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